src/librustc/middle/infer/error_reporting.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 //! Error Reporting Code for the inference engine
  12 //!
  13 //! Because of the way inference, and in particular region inference,
  14 //! works, it often happens that errors are not detected until far after
  15 //! the relevant line of code has been type-checked. Therefore, there is
  16 //! an elaborate system to track why a particular constraint in the
  17 //! inference graph arose so that we can explain to the user what gave
  18 //! rise to a particular error.
  19 //!
  20 //! The basis of the system are the "origin" types. An "origin" is the
  21 //! reason that a constraint or inference variable arose. There are
  22 //! different "origin" enums for different kinds of constraints/variables
  23 //! (e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has
  24 //! a span, but also more information so that we can generate a meaningful
  25 //! error message.
  26 //!
  27 //! Having a catalogue of all the different reasons an error can arise is
  28 //! also useful for other reasons, like cross-referencing FAQs etc, though
  29 //! we are not really taking advantage of this yet.
  30 //!
  31 //! # Region Inference
  32 //!
  33 //! Region inference is particularly tricky because it always succeeds "in
  34 //! the moment" and simply registers a constraint. Then, at the end, we
  35 //! can compute the full graph and report errors, so we need to be able to
  36 //! store and later report what gave rise to the conflicting constraints.
  37 //!
  38 //! # Subtype Trace
  39 //!
  40 //! Determining whether `T1 <: T2` often involves a number of subtypes and
  41 //! subconstraints along the way. A "TypeTrace" is an extended version
  42 //! of an origin that traces the types and other values that were being
  43 //! compared. It is not necessarily comprehensive (in fact, at the time of
  44 //! this writing it only tracks the root values being compared) but I'd
  45 //! like to extend it to include significant "waypoints". For example, if
  46 //! you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2
  47 //! <: T4` fails, I'd like the trace to include enough information to say
  48 //! "in the 2nd element of the tuple". Similarly, failures when comparing
  49 //! arguments or return types in fn types should be able to cite the
  50 //! specific position, etc.
  51 //!
  52 //! # Reality vs plan
  53 //!
  54 //! Of course, there is still a LOT of code in typeck that has yet to be
  55 //! ported to this system, and which relies on string concatenation at the
  56 //! time of error detection.
  57
  58 use self::FreshOrKept::*;
  59
  60 use super::InferCtxt;
  61 use super::TypeTrace;
  62 use super::SubregionOrigin;
  63 use super::RegionVariableOrigin;
  64 use super::ValuePairs;
  65 use super::region_inference::RegionResolutionError;
  66 use super::region_inference::ConcreteFailure;
  67 use super::region_inference::SubSupConflict;
  68 use super::region_inference::GenericBoundFailure;
  69 use super::region_inference::GenericKind;
  70 use super::region_inference::ProcessedErrors;
  71 use super::region_inference::SameRegions;
  72
  73 use std::collections::HashSet;
  74
  75 use front::map as ast_map;
  76 use rustc_front::hir;
  77 use rustc_front::print::pprust;
  78
  79 use middle::cstore::CrateStore;
  80 use middle::def;
  81 use middle::def_id::DefId;
  82 use middle::infer::{self, TypeOrigin};
  83 use middle::region;
  84 use middle::subst;
  85 use middle::ty::{self, Ty, HasTypeFlags};
  86 use middle::ty::{Region, ReFree};
  87 use middle::ty::error::TypeError;
  88
  89 use std::cell::{Cell, RefCell};
  90 use std::char::from_u32;
  91 use std::fmt;
  92 use syntax::ast;
  93 use syntax::errors::DiagnosticBuilder;
  94 use syntax::codemap::{self, Pos, Span};
  95 use syntax::parse::token;
  96 use syntax::ptr::P;
  97
  98 impl<'tcx> ty::ctxt<'tcx> {
  99     pub fn note_and_explain_region(&self,
 100                                    err: &mut DiagnosticBuilder,
 101                                    prefix: &str,
 102                                    region: ty::Region,
 103                                    suffix: &str) {
 104         fn item_scope_tag(item: &hir::Item) -> &'static str {
 105             match item.node {
 106                 hir::ItemImpl(..) => "impl",
 107                 hir::ItemStruct(..) => "struct",
 108                 hir::ItemEnum(..) => "enum",
 109                 hir::ItemTrait(..) => "trait",
 110                 hir::ItemFn(..) => "function body",
 111                 _ => "item"
 112             }
 113         }
 114
 115         fn explain_span(tcx: &ty::ctxt, heading: &str, span: Span)
 116                         -> (String, Option<Span>) {
 117             let lo = tcx.sess.codemap().lookup_char_pos_adj(span.lo);
 118             (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize()),
 119              Some(span))
 120         }
 121
 122         let (description, span) = match region {
 123             ty::ReScope(scope) => {
 124                 let new_string;
 125                 let unknown_scope = || {
 126                     format!("{}unknown scope: {:?}{}.  Please report a bug.",
 127                             prefix, scope, suffix)
 128                 };
 129                 let span = match scope.span(&self.region_maps, &self.map) {
 130                     Some(s) => s,
 131                     None => {
 132                         err.note(&unknown_scope());
 133                         return;
 134                     }
 135                 };
 136                 let tag = match self.map.find(scope.node_id(&self.region_maps)) {
 137                     Some(ast_map::NodeBlock(_)) => "block",
 138                     Some(ast_map::NodeExpr(expr)) => match expr.node {
 139                         hir::ExprCall(..) => "call",
 140                         hir::ExprMethodCall(..) => "method call",
 141                         hir::ExprMatch(_, _, hir::MatchSource::IfLetDesugar { .. }) => "if let",
 142                         hir::ExprMatch(_, _, hir::MatchSource::WhileLetDesugar) =>  "while let",
 143                         hir::ExprMatch(_, _, hir::MatchSource::ForLoopDesugar) =>  "for",
 144                         hir::ExprMatch(..) => "match",
 145                         _ => "expression",
 146                     },
 147                     Some(ast_map::NodeStmt(_)) => "statement",
 148                     Some(ast_map::NodeItem(it)) => item_scope_tag(&*it),
 149                     Some(_) | None => {
 150                         err.span_note(span, &unknown_scope());
 151                         return;
 152                     }
 153                 };
 154                 let scope_decorated_tag = match self.region_maps.code_extent_data(scope) {
 155                     region::CodeExtentData::Misc(_) => tag,
 156                     region::CodeExtentData::CallSiteScope { .. } => {
 157                         "scope of call-site for function"
 158                     }
 159                     region::CodeExtentData::ParameterScope { .. } => {
 160                         "scope of parameters for function"
 161                     }
 162                     region::CodeExtentData::DestructionScope(_) => {
 163                         new_string = format!("destruction scope surrounding {}", tag);
 164                         &new_string[..]
 165                     }
 166                     region::CodeExtentData::Remainder(r) => {
 167                         new_string = format!("block suffix following statement {}",
 168                                              r.first_statement_index);
 169                         &new_string[..]
 170                     }
 171                 };
 172                 explain_span(self, scope_decorated_tag, span)
 173             }
 174
 175             ty::ReFree(ref fr) => {
 176                 let prefix = match fr.bound_region {
 177                     ty::BrAnon(idx) => {
 178                         format!("the anonymous lifetime #{} defined on", idx + 1)
 179                     }
 180                     ty::BrFresh(_) => "an anonymous lifetime defined on".to_owned(),
 181                     _ => {
 182                         format!("the lifetime {} as defined on",
 183                                 fr.bound_region)
 184                     }
 185                 };
 186
 187                 match self.map.find(fr.scope.node_id(&self.region_maps)) {
 188                     Some(ast_map::NodeBlock(ref blk)) => {
 189                         let (msg, opt_span) = explain_span(self, "block", blk.span);
 190                         (format!("{} {}", prefix, msg), opt_span)
 191                     }
 192                     Some(ast_map::NodeItem(it)) => {
 193                         let tag = item_scope_tag(&*it);
 194                         let (msg, opt_span) = explain_span(self, tag, it.span);
 195                         (format!("{} {}", prefix, msg), opt_span)
 196                     }
 197                     Some(_) | None => {
 198                         // this really should not happen, but it does:
 199                         // FIXME(#27942)
 200                         (format!("{} unknown free region bounded by scope {:?}",
 201                                  prefix, fr.scope), None)
 202                     }
 203                 }
 204             }
 205
 206             ty::ReStatic => ("the static lifetime".to_owned(), None),
 207
 208             ty::ReEmpty => ("the empty lifetime".to_owned(), None),
 209
 210             ty::ReEarlyBound(ref data) => (data.name.to_string(), None),
 211
 212             // FIXME(#13998) ReSkolemized should probably print like
 213             // ReFree rather than dumping Debug output on the user.
 214             //
 215             // We shouldn't really be having unification failures with ReVar
 216             // and ReLateBound though.
 217             ty::ReSkolemized(..) | ty::ReVar(_) | ty::ReLateBound(..) => {
 218                 (format!("lifetime {:?}", region), None)
 219             }
 220         };
 221         let message = format!("{}{}{}", prefix, description, suffix);
 222         if let Some(span) = span {
 223             err.span_note(span, &message);
 224         } else {
 225             err.note(&message);
 226         }
 227     }
 228 }
 229
 230 pub trait ErrorReporting<'tcx> {
 231     fn report_region_errors(&self,
 232                             errors: &Vec<RegionResolutionError<'tcx>>);
 233
 234     fn process_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>)
 235                       -> Vec<RegionResolutionError<'tcx>>;
 236
 237     fn report_type_error(&self,
 238                          trace: TypeTrace<'tcx>,
 239                          terr: &TypeError<'tcx>)
 240                          -> Option<DiagnosticBuilder<'tcx>>;
 241
 242     fn check_and_note_conflicting_crates(&self,
 243                                          err: &mut DiagnosticBuilder,
 244                                          terr: &TypeError<'tcx>,
 245                                          sp: Span);
 246
 247     fn report_and_explain_type_error(&self,
 248                                      trace: TypeTrace<'tcx>,
 249                                      terr: &TypeError<'tcx>);
 250
 251     fn values_str(&self, values: &ValuePairs<'tcx>) -> Option<String>;
 252
 253     fn expected_found_str<T: fmt::Display + Resolvable<'tcx> + HasTypeFlags>(
 254         &self,
 255         exp_found: &ty::error::ExpectedFound<T>)
 256         -> Option<String>;
 257
 258     fn report_concrete_failure(&self,
 259                                origin: SubregionOrigin<'tcx>,
 260                                sub: Region,
 261                                sup: Region);
 262
 263     fn report_generic_bound_failure(&self,
 264                                     origin: SubregionOrigin<'tcx>,
 265                                     kind: GenericKind<'tcx>,
 266                                     sub: Region);
 267
 268     fn report_sub_sup_conflict(&self,
 269                                var_origin: RegionVariableOrigin,
 270                                sub_origin: SubregionOrigin<'tcx>,
 271                                sub_region: Region,
 272                                sup_origin: SubregionOrigin<'tcx>,
 273                                sup_region: Region);
 274
 275     fn report_processed_errors(&self,
 276                                var_origin: &[RegionVariableOrigin],
 277                                trace_origin: &[(TypeTrace<'tcx>, TypeError<'tcx>)],
 278                                same_regions: &[SameRegions]);
 279
 280     fn give_suggestion(&self, err: &mut DiagnosticBuilder, same_regions: &[SameRegions]);
 281 }
 282
 283 trait ErrorReportingHelpers<'tcx> {
 284     fn report_inference_failure(&self,
 285                                 var_origin: RegionVariableOrigin)
 286                                 -> DiagnosticBuilder<'tcx>;
 287
 288     fn note_region_origin(&self,
 289                           err: &mut DiagnosticBuilder,
 290                           origin: &SubregionOrigin<'tcx>);
 291
 292     fn give_expl_lifetime_param(&self,
 293                                 err: &mut DiagnosticBuilder,
 294                                 decl: &hir::FnDecl,
 295                                 unsafety: hir::Unsafety,
 296                                 constness: hir::Constness,
 297                                 name: ast::Name,
 298                                 opt_explicit_self: Option<&hir::ExplicitSelf_>,
 299                                 generics: &hir::Generics,
 300                                 span: Span);
 301 }
 302
 303 impl<'a, 'tcx> ErrorReporting<'tcx> for InferCtxt<'a, 'tcx> {
 304     fn report_region_errors(&self,
 305                             errors: &Vec<RegionResolutionError<'tcx>>) {
 306         let p_errors = self.process_errors(errors);
 307         let errors = if p_errors.is_empty() { errors } else { &p_errors };
 308         for error in errors {
 309             match error.clone() {
 310                 ConcreteFailure(origin, sub, sup) => {
 311                     self.report_concrete_failure(origin, sub, sup);
 312                 }
 313
 314                 GenericBoundFailure(kind, param_ty, sub) => {
 315                     self.report_generic_bound_failure(kind, param_ty, sub);
 316                 }
 317
 318                 SubSupConflict(var_origin,
 319                                sub_origin, sub_r,
 320                                sup_origin, sup_r) => {
 321                     self.report_sub_sup_conflict(var_origin,
 322                                                  sub_origin, sub_r,
 323                                                  sup_origin, sup_r);
 324                 }
 325
 326                 ProcessedErrors(ref var_origins,
 327                                 ref trace_origins,
 328                                 ref same_regions) => {
 329                     if !same_regions.is_empty() {
 330                         self.report_processed_errors(&var_origins[..],
 331                                                      &trace_origins[..],
 332                                                      &same_regions[..]);
 333                     }
 334                 }
 335             }
 336         }
 337     }
 338
 339     // This method goes through all the errors and try to group certain types
 340     // of error together, for the purpose of suggesting explicit lifetime
 341     // parameters to the user. This is done so that we can have a more
 342     // complete view of what lifetimes should be the same.
 343     // If the return value is an empty vector, it means that processing
 344     // failed (so the return value of this method should not be used)
 345     fn process_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>)
 346                       -> Vec<RegionResolutionError<'tcx>> {
 347         debug!("process_errors()");
 348         let mut var_origins = Vec::new();
 349         let mut trace_origins = Vec::new();
 350         let mut same_regions = Vec::new();
 351         let mut processed_errors = Vec::new();
 352         for error in errors {
 353             match error.clone() {
 354                 ConcreteFailure(origin, sub, sup) => {
 355                     debug!("processing ConcreteFailure");
 356                     let trace = match origin {
 357                         infer::Subtype(trace) => Some(trace),
 358                         _ => None,
 359                     };
 360                     match free_regions_from_same_fn(self.tcx, sub, sup) {
 361                         Some(ref same_frs) if trace.is_some() => {
 362                             let trace = trace.unwrap();
 363                             let terr = TypeError::RegionsDoesNotOutlive(sup,
 364                                                                         sub);
 365                             trace_origins.push((trace, terr));
 366                             append_to_same_regions(&mut same_regions, same_frs);
 367                         }
 368                         _ => processed_errors.push((*error).clone()),
 369                     }
 370                 }
 371                 SubSupConflict(var_origin, _, sub_r, _, sup_r) => {
 372                     debug!("processing SubSupConflict sub: {:?} sup: {:?}", sub_r, sup_r);
 373                     match free_regions_from_same_fn(self.tcx, sub_r, sup_r) {
 374                         Some(ref same_frs) => {
 375                             var_origins.push(var_origin);
 376                             append_to_same_regions(&mut same_regions, same_frs);
 377                         }
 378                         None => processed_errors.push((*error).clone()),
 379                     }
 380                 }
 381                 _ => ()  // This shouldn't happen
 382             }
 383         }
 384         if !same_regions.is_empty() {
 385             let common_scope_id = same_regions[0].scope_id;
 386             for sr in &same_regions {
 387                 // Since ProcessedErrors is used to reconstruct the function
 388                 // declaration, we want to make sure that they are, in fact,
 389                 // from the same scope
 390                 if sr.scope_id != common_scope_id {
 391                     debug!("returning empty result from process_errors because
 392                             {} != {}", sr.scope_id, common_scope_id);
 393                     return vec!();
 394                 }
 395             }
 396             let pe = ProcessedErrors(var_origins, trace_origins, same_regions);
 397             debug!("errors processed: {:?}", pe);
 398             processed_errors.push(pe);
 399         }
 400         return processed_errors;
 401
 402
 403         struct FreeRegionsFromSameFn {
 404             sub_fr: ty::FreeRegion,
 405             sup_fr: ty::FreeRegion,
 406             scope_id: ast::NodeId
 407         }
 408
 409         impl FreeRegionsFromSameFn {
 410             fn new(sub_fr: ty::FreeRegion,
 411                    sup_fr: ty::FreeRegion,
 412                    scope_id: ast::NodeId)
 413                    -> FreeRegionsFromSameFn {
 414                 FreeRegionsFromSameFn {
 415                     sub_fr: sub_fr,
 416                     sup_fr: sup_fr,
 417                     scope_id: scope_id
 418                 }
 419             }
 420         }
 421
 422         fn free_regions_from_same_fn(tcx: &ty::ctxt,
 423                                      sub: Region,
 424                                      sup: Region)
 425                                      -> Option<FreeRegionsFromSameFn> {
 426             debug!("free_regions_from_same_fn(sub={:?}, sup={:?})", sub, sup);
 427             let (scope_id, fr1, fr2) = match (sub, sup) {
 428                 (ReFree(fr1), ReFree(fr2)) => {
 429                     if fr1.scope != fr2.scope {
 430                         return None
 431                     }
 432                     assert!(fr1.scope == fr2.scope);
 433                     (fr1.scope.node_id(&tcx.region_maps), fr1, fr2)
 434                 },
 435                 _ => return None
 436             };
 437             let parent = tcx.map.get_parent(scope_id);
 438             let parent_node = tcx.map.find(parent);
 439             match parent_node {
 440                 Some(node) => match node {
 441                     ast_map::NodeItem(item) => match item.node {
 442                         hir::ItemFn(..) => {
 443                             Some(FreeRegionsFromSameFn::new(fr1, fr2, scope_id))
 444                         },
 445                         _ => None
 446                     },
 447                     ast_map::NodeImplItem(..) |
 448                     ast_map::NodeTraitItem(..) => {
 449                         Some(FreeRegionsFromSameFn::new(fr1, fr2, scope_id))
 450                     },
 451                     _ => None
 452                 },
 453                 None => {
 454                     debug!("no parent node of scope_id {}", scope_id);
 455                     None
 456                 }
 457             }
 458         }
 459
 460         fn append_to_same_regions(same_regions: &mut Vec<SameRegions>,
 461                                   same_frs: &FreeRegionsFromSameFn) {
 462             let scope_id = same_frs.scope_id;
 463             let (sub_fr, sup_fr) = (same_frs.sub_fr, same_frs.sup_fr);
 464             for sr in &mut *same_regions {
 465                 if sr.contains(&sup_fr.bound_region)
 466                    && scope_id == sr.scope_id {
 467                     sr.push(sub_fr.bound_region);
 468                     return
 469                 }
 470             }
 471             same_regions.push(SameRegions {
 472                 scope_id: scope_id,
 473                 regions: vec!(sub_fr.bound_region, sup_fr.bound_region)
 474             })
 475         }
 476     }
 477
 478     fn report_type_error(&self,
 479                          trace: TypeTrace<'tcx>,
 480                          terr: &TypeError<'tcx>)
 481                          -> Option<DiagnosticBuilder<'tcx>> {
 482         let expected_found_str = match self.values_str(&trace.values) {
 483             Some(v) => v,
 484             None => {
 485                 return None; /* derived error */
 486             }
 487         };
 488
 489         let mut err = struct_span_err!(self.tcx.sess,
 490                                        trace.origin.span(),
 491                                        E0308,
 492                                        "{}: {} ({})",
 493                                        trace.origin,
 494                                        expected_found_str,
 495                                        terr);
 496
 497         self.check_and_note_conflicting_crates(&mut err, terr, trace.origin.span());
 498
 499         match trace.origin {
 500             TypeOrigin::MatchExpressionArm(_, arm_span, source) => match source {
 501                 hir::MatchSource::IfLetDesugar{..} => {
 502                     err.span_note(arm_span, "`if let` arm with an incompatible type");
 503                 }
 504                 _ => {
 505                     err.span_note(arm_span, "match arm with an incompatible type");
 506                 }
 507             },
 508             _ => ()
 509         }
 510         Some(err)
 511     }
 512
 513     /// Adds a note if the types come from similarly named crates
 514     fn check_and_note_conflicting_crates(&self,
 515                                          err: &mut DiagnosticBuilder,
 516                                          terr: &TypeError<'tcx>,
 517                                          sp: Span) {
 518         let report_path_match = |err: &mut DiagnosticBuilder, did1: DefId, did2: DefId| {
 519             // Only external crates, if either is from a local
 520             // module we could have false positives
 521             if !(did1.is_local() || did2.is_local()) && did1.krate != did2.krate {
 522                 let exp_path = self.tcx.with_path(did1,
 523                                                   |p| p.map(|x| x.to_string())
 524                                                        .collect::<Vec<_>>());
 525                 let found_path = self.tcx.with_path(did2,
 526                                                     |p| p.map(|x| x.to_string())
 527                                                          .collect::<Vec<_>>());
 528                 // We compare strings because PathMod and PathName can be different
 529                 // for imported and non-imported crates
 530                 if exp_path == found_path {
 531                     let crate_name = self.tcx.sess.cstore.crate_name(did1.krate);
 532                     err.span_note(sp, &format!("Perhaps two different versions \
 533                                                 of crate `{}` are being used?",
 534                                                crate_name));
 535                 }
 536             }
 537         };
 538         match *terr {
 539             TypeError::Sorts(ref exp_found) => {
 540                 // if they are both "path types", there's a chance of ambiguity
 541                 // due to different versions of the same crate
 542                 match (&exp_found.expected.sty, &exp_found.found.sty) {
 543                     (&ty::TyEnum(ref exp_adt, _), &ty::TyEnum(ref found_adt, _)) |
 544                     (&ty::TyStruct(ref exp_adt, _), &ty::TyStruct(ref found_adt, _)) |
 545                     (&ty::TyEnum(ref exp_adt, _), &ty::TyStruct(ref found_adt, _)) |
 546                     (&ty::TyStruct(ref exp_adt, _), &ty::TyEnum(ref found_adt, _)) => {
 547                         report_path_match(err, exp_adt.did, found_adt.did);
 548                     },
 549                     _ => ()
 550                 }
 551             },
 552             TypeError::Traits(ref exp_found) => {
 553                 report_path_match(err, exp_found.expected, exp_found.found);
 554             },
 555             _ => () // FIXME(#22750) handle traits and stuff
 556         }
 557     }
 558
 559     fn report_and_explain_type_error(&self,
 560                                      trace: TypeTrace<'tcx>,
 561                                      terr: &TypeError<'tcx>) {
 562         let span = trace.origin.span();
 563         let err = self.report_type_error(trace, terr);
 564         err.map(|mut err| {
 565             self.tcx.note_and_explain_type_err(&mut err, terr, span);
 566             err.emit();
 567         });
 568     }
 569
 570     /// Returns a string of the form "expected `{}`, found `{}`", or None if this is a derived
 571     /// error.
 572     fn values_str(&self, values: &ValuePairs<'tcx>) -> Option<String> {
 573         match *values {
 574             infer::Types(ref exp_found) => self.expected_found_str(exp_found),
 575             infer::TraitRefs(ref exp_found) => self.expected_found_str(exp_found),
 576             infer::PolyTraitRefs(ref exp_found) => self.expected_found_str(exp_found)
 577         }
 578     }
 579
 580     fn expected_found_str<T: fmt::Display + Resolvable<'tcx> + HasTypeFlags>(
 581         &self,
 582         exp_found: &ty::error::ExpectedFound<T>)
 583         -> Option<String>
 584     {
 585         let expected = exp_found.expected.resolve(self);
 586         if expected.references_error() {
 587             return None;
 588         }
 589
 590         let found = exp_found.found.resolve(self);
 591         if found.references_error() {
 592             return None;
 593         }
 594
 595         Some(format!("expected `{}`, found `{}`",
 596                      expected,
 597                      found))
 598     }
 599
 600     fn report_generic_bound_failure(&self,
 601                                     origin: SubregionOrigin<'tcx>,
 602                                     bound_kind: GenericKind<'tcx>,
 603                                     sub: Region)
 604     {
 605         // FIXME: it would be better to report the first error message
 606         // with the span of the parameter itself, rather than the span
 607         // where the error was detected. But that span is not readily
 608         // accessible.
 609
 610         let labeled_user_string = match bound_kind {
 611             GenericKind::Param(ref p) =>
 612                 format!("the parameter type `{}`", p),
 613             GenericKind::Projection(ref p) =>
 614                 format!("the associated type `{}`", p),
 615         };
 616
 617         let mut err = match sub {
 618             ty::ReFree(ty::FreeRegion {bound_region: ty::BrNamed(..), ..}) => {
 619                 // Does the required lifetime have a nice name we can print?
 620                 let mut err = struct_span_err!(self.tcx.sess,
 621                                                origin.span(),
 622                                                E0309,
 623                                                "{} may not live long enough",
 624                                                labeled_user_string);
 625                 err.fileline_help(origin.span(),
 626                                   &format!("consider adding an explicit lifetime bound `{}: {}`...",
 627                                            bound_kind,
 628                                            sub));
 629                 err
 630             }
 631
 632             ty::ReStatic => {
 633                 // Does the required lifetime have a nice name we can print?
 634                 let mut err = struct_span_err!(self.tcx.sess,
 635                                                origin.span(),
 636                                                E0310,
 637                                                "{} may not live long enough",
 638                                                labeled_user_string);
 639                 err.fileline_help(origin.span(),
 640                                   &format!("consider adding an explicit lifetime \
 641                                             bound `{}: 'static`...",
 642                                            bound_kind));
 643                 err
 644             }
 645
 646             _ => {
 647                 // If not, be less specific.
 648                 let mut err = struct_span_err!(self.tcx.sess,
 649                                                origin.span(),
 650                                                E0311,
 651                                                "{} may not live long enough",
 652                                                labeled_user_string);
 653                 err.fileline_help(origin.span(),
 654                                   &format!("consider adding an explicit lifetime bound for `{}`",
 655                                            bound_kind));
 656                 self.tcx.note_and_explain_region(
 657                     &mut err,
 658                     &format!("{} must be valid for ", labeled_user_string),
 659                     sub,
 660                     "...");
 661                 err
 662             }
 663         };
 664
 665         self.note_region_origin(&mut err, &origin);
 666         err.emit();
 667     }
 668
 669     fn report_concrete_failure(&self,
 670                                origin: SubregionOrigin<'tcx>,
 671                                sub: Region,
 672                                sup: Region) {
 673         match origin {
 674             infer::Subtype(trace) => {
 675                 let terr = TypeError::RegionsDoesNotOutlive(sup, sub);
 676                 self.report_and_explain_type_error(trace, &terr);
 677             }
 678             infer::Reborrow(span) => {
 679                 let mut err = struct_span_err!(self.tcx.sess, span, E0312,
 680                     "lifetime of reference outlines \
 681                      lifetime of borrowed content...");
 682                 self.tcx.note_and_explain_region(&mut err,
 683                     "...the reference is valid for ",
 684                     sub,
 685                     "...");
 686                 self.tcx.note_and_explain_region(&mut err,
 687                     "...but the borrowed content is only valid for ",
 688                     sup,
 689                     "");
 690                 err.emit();
 691             }
 692             infer::ReborrowUpvar(span, ref upvar_id) => {
 693                 let mut err = struct_span_err!(self.tcx.sess, span, E0313,
 694                     "lifetime of borrowed pointer outlives \
 695                             lifetime of captured variable `{}`...",
 696                             self.tcx.local_var_name_str(upvar_id.var_id));
 697                 self.tcx.note_and_explain_region(&mut err,
 698                     "...the borrowed pointer is valid for ",
 699                     sub,
 700                     "...");
 701                 self.tcx.note_and_explain_region(&mut err,
 702                     &format!("...but `{}` is only valid for ",
 703                              self.tcx.local_var_name_str(upvar_id.var_id)),
 704                     sup,
 705                     "");
 706                 err.emit();
 707             }
 708             infer::InfStackClosure(span) => {
 709                 let mut err = struct_span_err!(self.tcx.sess, span, E0314,
 710                     "closure outlives stack frame");
 711                 self.tcx.note_and_explain_region(&mut err,
 712                     "...the closure must be valid for ",
 713                     sub,
 714                     "...");
 715                 self.tcx.note_and_explain_region(&mut err,
 716                     "...but the closure's stack frame is only valid for ",
 717                     sup,
 718                     "");
 719                 err.emit();
 720             }
 721             infer::InvokeClosure(span) => {
 722                 let mut err = struct_span_err!(self.tcx.sess, span, E0315,
 723                     "cannot invoke closure outside of its lifetime");
 724                 self.tcx.note_and_explain_region(&mut err,
 725                     "the closure is only valid for ",
 726                     sup,
 727                     "");
 728                 err.emit();
 729             }
 730             infer::DerefPointer(span) => {
 731                 let mut err = struct_span_err!(self.tcx.sess, span, E0473,
 732                           "dereference of reference outside its lifetime");
 733                 self.tcx.note_and_explain_region(&mut err,
 734                     "the reference is only valid for ",
 735                     sup,
 736                     "");
 737                 err.emit();
 738             }
 739             infer::FreeVariable(span, id) => {
 740                 let mut err = struct_span_err!(self.tcx.sess, span, E0474,
 741                           "captured variable `{}` does not outlive the enclosing closure",
 742                           self.tcx.local_var_name_str(id));
 743                 self.tcx.note_and_explain_region(&mut err,
 744                     "captured variable is valid for ",
 745                     sup,
 746                     "");
 747                 self.tcx.note_and_explain_region(&mut err,
 748                     "closure is valid for ",
 749                     sub,
 750                     "");
 751                 err.emit();
 752             }
 753             infer::IndexSlice(span) => {
 754                 let mut err = struct_span_err!(self.tcx.sess, span, E0475,
 755                           "index of slice outside its lifetime");
 756                 self.tcx.note_and_explain_region(&mut err,
 757                     "the slice is only valid for ",
 758                     sup,
 759                     "");
 760                 err.emit();
 761             }
 762             infer::RelateObjectBound(span) => {
 763                 let mut err = struct_span_err!(self.tcx.sess, span, E0476,
 764                           "lifetime of the source pointer does not outlive \
 765                            lifetime bound of the object type");
 766                 self.tcx.note_and_explain_region(&mut err,
 767                     "object type is valid for ",
 768                     sub,
 769                     "");
 770                 self.tcx.note_and_explain_region(&mut err,
 771                     "source pointer is only valid for ",
 772                     sup,
 773                     "");
 774                 err.emit();
 775             }
 776             infer::RelateParamBound(span, ty) => {
 777                 let mut err = struct_span_err!(self.tcx.sess, span, E0477,
 778                           "the type `{}` does not fulfill the required lifetime",
 779                           self.ty_to_string(ty));
 780                 self.tcx.note_and_explain_region(&mut err,
 781                                         "type must outlive ",
 782                                         sub,
 783                                         "");
 784                 err.emit();
 785             }
 786             infer::RelateRegionParamBound(span) => {
 787                 let mut err = struct_span_err!(self.tcx.sess, span, E0478,
 788                           "lifetime bound not satisfied");
 789                 self.tcx.note_and_explain_region(&mut err,
 790                     "lifetime parameter instantiated with ",
 791                     sup,
 792                     "");
 793                 self.tcx.note_and_explain_region(&mut err,
 794                     "but lifetime parameter must outlive ",
 795                     sub,
 796                     "");
 797                 err.emit();
 798             }
 799             infer::RelateDefaultParamBound(span, ty) => {
 800                 let mut err = struct_span_err!(self.tcx.sess, span, E0479,
 801                           "the type `{}` (provided as the value of \
 802                            a type parameter) is not valid at this point",
 803                           self.ty_to_string(ty));
 804                 self.tcx.note_and_explain_region(&mut err,
 805                                         "type must outlive ",
 806                                         sub,
 807                                         "");
 808                 err.emit();
 809             }
 810             infer::CallRcvr(span) => {
 811                 let mut err = struct_span_err!(self.tcx.sess, span, E0480,
 812                           "lifetime of method receiver does not outlive \
 813                            the method call");
 814                 self.tcx.note_and_explain_region(&mut err,
 815                     "the receiver is only valid for ",
 816                     sup,
 817                     "");
 818                 err.emit();
 819             }
 820             infer::CallArg(span) => {
 821                 let mut err = struct_span_err!(self.tcx.sess, span, E0481,
 822                           "lifetime of function argument does not outlive \
 823                            the function call");
 824                 self.tcx.note_and_explain_region(&mut err,
 825                     "the function argument is only valid for ",
 826                     sup,
 827                     "");
 828                 err.emit();
 829             }
 830             infer::CallReturn(span) => {
 831                 let mut err = struct_span_err!(self.tcx.sess, span, E0482,
 832                           "lifetime of return value does not outlive \
 833                            the function call");
 834                 self.tcx.note_and_explain_region(&mut err,
 835                     "the return value is only valid for ",
 836                     sup,
 837                     "");
 838                 err.emit();
 839             }
 840             infer::Operand(span) => {
 841                 let mut err = struct_span_err!(self.tcx.sess, span, E0483,
 842                           "lifetime of operand does not outlive \
 843                            the operation");
 844                 self.tcx.note_and_explain_region(&mut err,
 845                     "the operand is only valid for ",
 846                     sup,
 847                     "");
 848                 err.emit();
 849             }
 850             infer::AddrOf(span) => {
 851                 let mut err = struct_span_err!(self.tcx.sess, span, E0484,
 852                           "reference is not valid at the time of borrow");
 853                 self.tcx.note_and_explain_region(&mut err,
 854                     "the borrow is only valid for ",
 855                     sup,
 856                     "");
 857                 err.emit();
 858             }
 859             infer::AutoBorrow(span) => {
 860                 let mut err = struct_span_err!(self.tcx.sess, span, E0485,
 861                           "automatically reference is not valid \
 862                            at the time of borrow");
 863                 self.tcx.note_and_explain_region(&mut err,
 864                     "the automatic borrow is only valid for ",
 865                     sup,
 866                     "");
 867                 err.emit();
 868             }
 869             infer::ExprTypeIsNotInScope(t, span) => {
 870                 let mut err = struct_span_err!(self.tcx.sess, span, E0486,
 871                           "type of expression contains references \
 872                            that are not valid during the expression: `{}`",
 873                           self.ty_to_string(t));
 874                 self.tcx.note_and_explain_region(&mut err,
 875                     "type is only valid for ",
 876                     sup,
 877                     "");
 878                 err.emit();
 879             }
 880             infer::SafeDestructor(span) => {
 881                 let mut err = struct_span_err!(self.tcx.sess, span, E0487,
 882                           "unsafe use of destructor: destructor might be called \
 883                            while references are dead");
 884                 // FIXME (22171): terms "super/subregion" are suboptimal
 885                 self.tcx.note_and_explain_region(&mut err,
 886                     "superregion: ",
 887                     sup,
 888                     "");
 889                 self.tcx.note_and_explain_region(&mut err,
 890                     "subregion: ",
 891                     sub,
 892                     "");
 893                 err.emit();
 894             }
 895             infer::BindingTypeIsNotValidAtDecl(span) => {
 896                 let mut err = struct_span_err!(self.tcx.sess, span, E0488,
 897                           "lifetime of variable does not enclose its declaration");
 898                 self.tcx.note_and_explain_region(&mut err,
 899                     "the variable is only valid for ",
 900                     sup,
 901                     "");
 902                 err.emit();
 903             }
 904             infer::ParameterInScope(_, span) => {
 905                 let mut err = struct_span_err!(self.tcx.sess, span, E0489,
 906                           "type/lifetime parameter not in scope here");
 907                 self.tcx.note_and_explain_region(&mut err,
 908                     "the parameter is only valid for ",
 909                     sub,
 910                     "");
 911                 err.emit();
 912             }
 913             infer::DataBorrowed(ty, span) => {
 914                 let mut err = struct_span_err!(self.tcx.sess, span, E0490,
 915                           "a value of type `{}` is borrowed for too long",
 916                           self.ty_to_string(ty));
 917                 self.tcx.note_and_explain_region(&mut err, "the type is valid for ", sub, "");
 918                 self.tcx.note_and_explain_region(&mut err, "but the borrow lasts for ", sup, "");
 919                 err.emit();
 920             }
 921             infer::ReferenceOutlivesReferent(ty, span) => {
 922                 let mut err = struct_span_err!(self.tcx.sess, span, E0491,
 923                           "in type `{}`, reference has a longer lifetime \
 924                            than the data it references",
 925                           self.ty_to_string(ty));
 926                 self.tcx.note_and_explain_region(&mut err,
 927                     "the pointer is valid for ",
 928                     sub,
 929                     "");
 930                 self.tcx.note_and_explain_region(&mut err,
 931                     "but the referenced data is only valid for ",
 932                     sup,
 933                     "");
 934                 err.emit();
 935             }
 936         }
 937     }
 938
 939     fn report_sub_sup_conflict(&self,
 940                                var_origin: RegionVariableOrigin,
 941                                sub_origin: SubregionOrigin<'tcx>,
 942                                sub_region: Region,
 943                                sup_origin: SubregionOrigin<'tcx>,
 944                                sup_region: Region) {
 945         let mut err = self.report_inference_failure(var_origin);
 946
 947         self.tcx.note_and_explain_region(&mut err,
 948             "first, the lifetime cannot outlive ",
 949             sup_region,
 950             "...");
 951
 952         self.note_region_origin(&mut err, &sup_origin);
 953
 954         self.tcx.note_and_explain_region(&mut err,
 955             "but, the lifetime must be valid for ",
 956             sub_region,
 957             "...");
 958
 959         self.note_region_origin(&mut err, &sub_origin);
 960         err.emit();
 961     }
 962
 963     fn report_processed_errors(&self,
 964                                var_origins: &[RegionVariableOrigin],
 965                                trace_origins: &[(TypeTrace<'tcx>, TypeError<'tcx>)],
 966                                same_regions: &[SameRegions]) {
 967         for (i, vo) in var_origins.iter().enumerate() {
 968             let mut err = self.report_inference_failure(vo.clone());
 969             if i == var_origins.len() - 1 {
 970                 self.give_suggestion(&mut err, same_regions);
 971             }
 972             err.emit();
 973         }
 974
 975         for &(ref trace, ref terr) in trace_origins {
 976             self.report_and_explain_type_error(trace.clone(), terr);
 977         }
 978     }
 979
 980     fn give_suggestion(&self, err: &mut DiagnosticBuilder, same_regions: &[SameRegions]) {
 981         let scope_id = same_regions[0].scope_id;
 982         let parent = self.tcx.map.get_parent(scope_id);
 983         let parent_node = self.tcx.map.find(parent);
 984         let taken = lifetimes_in_scope(self.tcx, scope_id);
 985         let life_giver = LifeGiver::with_taken(&taken[..]);
 986         let node_inner = match parent_node {
 987             Some(ref node) => match *node {
 988                 ast_map::NodeItem(ref item) => {
 989                     match item.node {
 990                         hir::ItemFn(ref fn_decl, unsafety, constness, _, ref gen, _) => {
 991                             Some((fn_decl, gen, unsafety, constness,
 992                                   item.name, None, item.span))
 993                         },
 994                         _ => None
 995                     }
 996                 }
 997                 ast_map::NodeImplItem(item) => {
 998                     match item.node {
 999                         hir::ImplItemKind::Method(ref sig, _) => {
1000                             Some((&sig.decl,
1001                                   &sig.generics,
1002                                   sig.unsafety,
1003                                   sig.constness,
1004                                   item.name,
1005                                   Some(&sig.explicit_self.node),
1006                                   item.span))
1007                         }
1008                         _ => None,
1009                     }
1010                 },
1011                 ast_map::NodeTraitItem(item) => {
1012                     match item.node {
1013                         hir::MethodTraitItem(ref sig, Some(_)) => {
1014                             Some((&sig.decl,
1015                                   &sig.generics,
1016                                   sig.unsafety,
1017                                   sig.constness,
1018                                   item.name,
1019                                   Some(&sig.explicit_self.node),
1020                                   item.span))
1021                         }
1022                         _ => None
1023                     }
1024                 }
1025                 _ => None
1026             },
1027             None => None
1028         };
1029         let (fn_decl, generics, unsafety, constness, name, expl_self, span)
1030                                     = node_inner.expect("expect item fn");
1031         let rebuilder = Rebuilder::new(self.tcx, fn_decl, expl_self,
1032                                        generics, same_regions, &life_giver);
1033         let (fn_decl, expl_self, generics) = rebuilder.rebuild();
1034         self.give_expl_lifetime_param(err, &fn_decl, unsafety, constness, name,
1035                                       expl_self.as_ref(), &generics, span);
1036     }
1037 }
1038
1039 struct RebuildPathInfo<'a> {
1040     path: &'a hir::Path,
1041     // indexes to insert lifetime on path.lifetimes
1042     indexes: Vec<u32>,
1043     // number of lifetimes we expect to see on the type referred by `path`
1044     // (e.g., expected=1 for struct Foo<'a>)
1045     expected: u32,
1046     anon_nums: &'a HashSet<u32>,
1047     region_names: &'a HashSet<ast::Name>
1048 }
1049
1050 struct Rebuilder<'a, 'tcx: 'a> {
1051     tcx: &'a ty::ctxt<'tcx>,
1052     fn_decl: &'a hir::FnDecl,
1053     expl_self_opt: Option<&'a hir::ExplicitSelf_>,
1054     generics: &'a hir::Generics,
1055     same_regions: &'a [SameRegions],
1056     life_giver: &'a LifeGiver,
1057     cur_anon: Cell<u32>,
1058     inserted_anons: RefCell<HashSet<u32>>,
1059 }
1060
1061 enum FreshOrKept {
1062     Fresh,
1063     Kept
1064 }
1065
1066 impl<'a, 'tcx> Rebuilder<'a, 'tcx> {
1067     fn new(tcx: &'a ty::ctxt<'tcx>,
1068            fn_decl: &'a hir::FnDecl,
1069            expl_self_opt: Option<&'a hir::ExplicitSelf_>,
1070            generics: &'a hir::Generics,
1071            same_regions: &'a [SameRegions],
1072            life_giver: &'a LifeGiver)
1073            -> Rebuilder<'a, 'tcx> {
1074         Rebuilder {
1075             tcx: tcx,
1076             fn_decl: fn_decl,
1077             expl_self_opt: expl_self_opt,
1078             generics: generics,
1079             same_regions: same_regions,
1080             life_giver: life_giver,
1081             cur_anon: Cell::new(0),
1082             inserted_anons: RefCell::new(HashSet::new()),
1083         }
1084     }
1085
1086     fn rebuild(&self)
1087                -> (hir::FnDecl, Option<hir::ExplicitSelf_>, hir::Generics) {
1088         let mut expl_self_opt = self.expl_self_opt.cloned();
1089         let mut inputs = self.fn_decl.inputs.clone();
1090         let mut output = self.fn_decl.output.clone();
1091         let mut ty_params = self.generics.ty_params.clone();
1092         let where_clause = self.generics.where_clause.clone();
1093         let mut kept_lifetimes = HashSet::new();
1094         for sr in self.same_regions {
1095             self.cur_anon.set(0);
1096             self.offset_cur_anon();
1097             let (anon_nums, region_names) =
1098                                 self.extract_anon_nums_and_names(sr);
1099             let (lifetime, fresh_or_kept) = self.pick_lifetime(&region_names);
1100             match fresh_or_kept {
1101                 Kept => { kept_lifetimes.insert(lifetime.name); }
1102                 _ => ()
1103             }
1104             expl_self_opt = self.rebuild_expl_self(expl_self_opt, lifetime,
1105                                                    &anon_nums, &region_names);
1106             inputs = self.rebuild_args_ty(&inputs[..], lifetime,
1107                                           &anon_nums, &region_names);
1108             output = self.rebuild_output(&output, lifetime, &anon_nums, &region_names);
1109             ty_params = self.rebuild_ty_params(ty_params, lifetime,
1110                                                &region_names);
1111         }
1112         let fresh_lifetimes = self.life_giver.get_generated_lifetimes();
1113         let all_region_names = self.extract_all_region_names();
1114         let generics = self.rebuild_generics(self.generics,
1115                                              &fresh_lifetimes,
1116                                              &kept_lifetimes,
1117                                              &all_region_names,
1118                                              ty_params,
1119                                              where_clause);
1120         let new_fn_decl = hir::FnDecl {
1121             inputs: inputs,
1122             output: output,
1123             variadic: self.fn_decl.variadic
1124         };
1125         (new_fn_decl, expl_self_opt, generics)
1126     }
1127
1128     fn pick_lifetime(&self,
1129                      region_names: &HashSet<ast::Name>)
1130                      -> (hir::Lifetime, FreshOrKept) {
1131         if !region_names.is_empty() {
1132             // It's not necessary to convert the set of region names to a
1133             // vector of string and then sort them. However, it makes the
1134             // choice of lifetime name deterministic and thus easier to test.
1135             let mut names = Vec::new();
1136             for rn in region_names {
1137                 let lt_name = rn.to_string();
1138                 names.push(lt_name);
1139             }
1140             names.sort();
1141             let name = token::intern(&names[0]);
1142             return (name_to_dummy_lifetime(name), Kept);
1143         }
1144         return (self.life_giver.give_lifetime(), Fresh);
1145     }
1146
1147     fn extract_anon_nums_and_names(&self, same_regions: &SameRegions)
1148                                    -> (HashSet<u32>, HashSet<ast::Name>) {
1149         let mut anon_nums = HashSet::new();
1150         let mut region_names = HashSet::new();
1151         for br in &same_regions.regions {
1152             match *br {
1153                 ty::BrAnon(i) => {
1154                     anon_nums.insert(i);
1155                 }
1156                 ty::BrNamed(_, name) => {
1157                     region_names.insert(name);
1158                 }
1159                 _ => ()
1160             }
1161         }
1162         (anon_nums, region_names)
1163     }
1164
1165     fn extract_all_region_names(&self) -> HashSet<ast::Name> {
1166         let mut all_region_names = HashSet::new();
1167         for sr in self.same_regions {
1168             for br in &sr.regions {
1169                 match *br {
1170                     ty::BrNamed(_, name) => {
1171                         all_region_names.insert(name);
1172                     }
1173                     _ => ()
1174                 }
1175             }
1176         }
1177         all_region_names
1178     }
1179
1180     fn inc_cur_anon(&self, n: u32) {
1181         let anon = self.cur_anon.get();
1182         self.cur_anon.set(anon+n);
1183     }
1184
1185     fn offset_cur_anon(&self) {
1186         let mut anon = self.cur_anon.get();
1187         while self.inserted_anons.borrow().contains(&anon) {
1188             anon += 1;
1189         }
1190         self.cur_anon.set(anon);
1191     }
1192
1193     fn inc_and_offset_cur_anon(&self, n: u32) {
1194         self.inc_cur_anon(n);
1195         self.offset_cur_anon();
1196     }
1197
1198     fn track_anon(&self, anon: u32) {
1199         self.inserted_anons.borrow_mut().insert(anon);
1200     }
1201
1202     fn rebuild_ty_params(&self,
1203                          ty_params: hir::HirVec<hir::TyParam>,
1204                          lifetime: hir::Lifetime,
1205                          region_names: &HashSet<ast::Name>)
1206                          -> hir::HirVec<hir::TyParam> {
1207         ty_params.iter().map(|ty_param| {
1208             let bounds = self.rebuild_ty_param_bounds(ty_param.bounds.clone(),
1209                                                       lifetime,
1210                                                       region_names);
1211             hir::TyParam {
1212                 name: ty_param.name,
1213                 id: ty_param.id,
1214                 bounds: bounds,
1215                 default: ty_param.default.clone(),
1216                 span: ty_param.span,
1217             }
1218         }).collect()
1219     }
1220
1221     fn rebuild_ty_param_bounds(&self,
1222                                ty_param_bounds: hir::TyParamBounds,
1223                                lifetime: hir::Lifetime,
1224                                region_names: &HashSet<ast::Name>)
1225                                -> hir::TyParamBounds {
1226         ty_param_bounds.iter().map(|tpb| {
1227             match tpb {
1228                 &hir::RegionTyParamBound(lt) => {
1229                     // FIXME -- it's unclear whether I'm supposed to
1230                     // substitute lifetime here. I suspect we need to
1231                     // be passing down a map.
1232                     hir::RegionTyParamBound(lt)
1233                 }
1234                 &hir::TraitTyParamBound(ref poly_tr, modifier) => {
1235                     let tr = &poly_tr.trait_ref;
1236                     let last_seg = tr.path.segments.last().unwrap();
1237                     let mut insert = Vec::new();
1238                     let lifetimes = last_seg.parameters.lifetimes();
1239                     for (i, lt) in lifetimes.iter().enumerate() {
1240                         if region_names.contains(&lt.name) {
1241                             insert.push(i as u32);
1242                         }
1243                     }
1244                     let rebuild_info = RebuildPathInfo {
1245                         path: &tr.path,
1246                         indexes: insert,
1247                         expected: lifetimes.len() as u32,
1248                         anon_nums: &HashSet::new(),
1249                         region_names: region_names
1250                     };
1251                     let new_path = self.rebuild_path(rebuild_info, lifetime);
1252                     hir::TraitTyParamBound(hir::PolyTraitRef {
1253                         bound_lifetimes: poly_tr.bound_lifetimes.clone(),
1254                         trait_ref: hir::TraitRef {
1255                             path: new_path,
1256                             ref_id: tr.ref_id,
1257                         },
1258                         span: poly_tr.span,
1259                     }, modifier)
1260                 }
1261             }
1262         }).collect()
1263     }
1264
1265     fn rebuild_expl_self(&self,
1266                          expl_self_opt: Option<hir::ExplicitSelf_>,
1267                          lifetime: hir::Lifetime,
1268                          anon_nums: &HashSet<u32>,
1269                          region_names: &HashSet<ast::Name>)
1270                          -> Option<hir::ExplicitSelf_> {
1271         match expl_self_opt {
1272             Some(ref expl_self) => match *expl_self {
1273                 hir::SelfRegion(lt_opt, muta, id) => match lt_opt {
1274                     Some(lt) => if region_names.contains(&lt.name) {
1275                         return Some(hir::SelfRegion(Some(lifetime), muta, id));
1276                     },
1277                     None => {
1278                         let anon = self.cur_anon.get();
1279                         self.inc_and_offset_cur_anon(1);
1280                         if anon_nums.contains(&anon) {
1281                             self.track_anon(anon);
1282                             return Some(hir::SelfRegion(Some(lifetime), muta, id));
1283                         }
1284                     }
1285                 },
1286                 _ => ()
1287             },
1288             None => ()
1289         }
1290         expl_self_opt
1291     }
1292
1293     fn rebuild_generics(&self,
1294                         generics: &hir::Generics,
1295                         add: &Vec<hir::Lifetime>,
1296                         keep: &HashSet<ast::Name>,
1297                         remove: &HashSet<ast::Name>,
1298                         ty_params: hir::HirVec<hir::TyParam>,
1299                         where_clause: hir::WhereClause)
1300                         -> hir::Generics {
1301         let mut lifetimes = Vec::new();
1302         for lt in add {
1303             lifetimes.push(hir::LifetimeDef { lifetime: *lt,
1304                                               bounds: hir::HirVec::new() });
1305         }
1306         for lt in &generics.lifetimes {
1307             if keep.contains(&lt.lifetime.name) ||
1308                 !remove.contains(&lt.lifetime.name) {
1309                 lifetimes.push((*lt).clone());
1310             }
1311         }
1312         hir::Generics {
1313             lifetimes: lifetimes.into(),
1314             ty_params: ty_params,
1315             where_clause: where_clause,
1316         }
1317     }
1318
1319     fn rebuild_args_ty(&self,
1320                        inputs: &[hir::Arg],
1321                        lifetime: hir::Lifetime,
1322                        anon_nums: &HashSet<u32>,
1323                        region_names: &HashSet<ast::Name>)
1324                        -> hir::HirVec<hir::Arg> {
1325         let mut new_inputs = Vec::new();
1326         for arg in inputs {
1327             let new_ty = self.rebuild_arg_ty_or_output(&*arg.ty, lifetime,
1328                                                        anon_nums, region_names);
1329             let possibly_new_arg = hir::Arg {
1330                 ty: new_ty,
1331                 pat: arg.pat.clone(),
1332                 id: arg.id
1333             };
1334             new_inputs.push(possibly_new_arg);
1335         }
1336         new_inputs.into()
1337     }
1338
1339     fn rebuild_output(&self, ty: &hir::FunctionRetTy,
1340                       lifetime: hir::Lifetime,
1341                       anon_nums: &HashSet<u32>,
1342                       region_names: &HashSet<ast::Name>) -> hir::FunctionRetTy {
1343         match *ty {
1344             hir::Return(ref ret_ty) => hir::Return(
1345                 self.rebuild_arg_ty_or_output(&**ret_ty, lifetime, anon_nums, region_names)
1346             ),
1347             hir::DefaultReturn(span) => hir::DefaultReturn(span),
1348             hir::NoReturn(span) => hir::NoReturn(span)
1349         }
1350     }
1351
1352     fn rebuild_arg_ty_or_output(&self,
1353                                 ty: &hir::Ty,
1354                                 lifetime: hir::Lifetime,
1355                                 anon_nums: &HashSet<u32>,
1356                                 region_names: &HashSet<ast::Name>)
1357                                 -> P<hir::Ty> {
1358         let mut new_ty = P(ty.clone());
1359         let mut ty_queue = vec!(ty);
1360         while !ty_queue.is_empty() {
1361             let cur_ty = ty_queue.remove(0);
1362             match cur_ty.node {
1363                 hir::TyRptr(lt_opt, ref mut_ty) => {
1364                     let rebuild = match lt_opt {
1365                         Some(lt) => region_names.contains(&lt.name),
1366                         None => {
1367                             let anon = self.cur_anon.get();
1368                             let rebuild = anon_nums.contains(&anon);
1369                             if rebuild {
1370                                 self.track_anon(anon);
1371                             }
1372                             self.inc_and_offset_cur_anon(1);
1373                             rebuild
1374                         }
1375                     };
1376                     if rebuild {
1377                         let to = hir::Ty {
1378                             id: cur_ty.id,
1379                             node: hir::TyRptr(Some(lifetime), mut_ty.clone()),
1380                             span: cur_ty.span
1381                         };
1382                         new_ty = self.rebuild_ty(new_ty, P(to));
1383                     }
1384                     ty_queue.push(&*mut_ty.ty);
1385                 }
1386                 hir::TyPath(ref maybe_qself, ref path) => {
1387                     let a_def = match self.tcx.def_map.borrow().get(&cur_ty.id) {
1388                         None => {
1389                             self.tcx
1390                                 .sess
1391                                 .fatal(&format!(
1392                                         "unbound path {}",
1393                                         pprust::path_to_string(path)))
1394                         }
1395                         Some(d) => d.full_def()
1396                     };
1397                     match a_def {
1398                         def::DefTy(did, _) | def::DefStruct(did) => {
1399                             let generics = self.tcx.lookup_item_type(did).generics;
1400
1401                             let expected =
1402                                 generics.regions.len(subst::TypeSpace) as u32;
1403                             let lifetimes =
1404                                 path.segments.last().unwrap().parameters.lifetimes();
1405                             let mut insert = Vec::new();
1406                             if lifetimes.is_empty() {
1407                                 let anon = self.cur_anon.get();
1408                                 for (i, a) in (anon..anon+expected).enumerate() {
1409                                     if anon_nums.contains(&a) {
1410                                         insert.push(i as u32);
1411                                     }
1412                                     self.track_anon(a);
1413                                 }
1414                                 self.inc_and_offset_cur_anon(expected);
1415                             } else {
1416                                 for (i, lt) in lifetimes.iter().enumerate() {
1417                                     if region_names.contains(&lt.name) {
1418                                         insert.push(i as u32);
1419                                     }
1420                                 }
1421                             }
1422                             let rebuild_info = RebuildPathInfo {
1423                                 path: path,
1424                                 indexes: insert,
1425                                 expected: expected,
1426                                 anon_nums: anon_nums,
1427                                 region_names: region_names
1428                             };
1429                             let new_path = self.rebuild_path(rebuild_info, lifetime);
1430                             let qself = maybe_qself.as_ref().map(|qself| {
1431                                 hir::QSelf {
1432                                     ty: self.rebuild_arg_ty_or_output(&qself.ty, lifetime,
1433                                                                       anon_nums, region_names),
1434                                     position: qself.position
1435                                 }
1436                             });
1437                             let to = hir::Ty {
1438                                 id: cur_ty.id,
1439                                 node: hir::TyPath(qself, new_path),
1440                                 span: cur_ty.span
1441                             };
1442                             new_ty = self.rebuild_ty(new_ty, P(to));
1443                         }
1444                         _ => ()
1445                     }
1446
1447                 }
1448
1449                 hir::TyPtr(ref mut_ty) => {
1450                     ty_queue.push(&*mut_ty.ty);
1451                 }
1452                 hir::TyVec(ref ty) |
1453                 hir::TyFixedLengthVec(ref ty, _) => {
1454                     ty_queue.push(&**ty);
1455                 }
1456                 hir::TyTup(ref tys) => ty_queue.extend(tys.iter().map(|ty| &**ty)),
1457                 _ => {}
1458             }
1459         }
1460         new_ty
1461     }
1462
1463     fn rebuild_ty(&self,
1464                   from: P<hir::Ty>,
1465                   to: P<hir::Ty>)
1466                   -> P<hir::Ty> {
1467
1468         fn build_to(from: P<hir::Ty>,
1469                     to: &mut Option<P<hir::Ty>>)
1470                     -> P<hir::Ty> {
1471             if Some(from.id) == to.as_ref().map(|ty| ty.id) {
1472                 return to.take().expect("`to` type found more than once during rebuild");
1473             }
1474             from.map(|hir::Ty {id, node, span}| {
1475                 let new_node = match node {
1476                     hir::TyRptr(lifetime, mut_ty) => {
1477                         hir::TyRptr(lifetime, hir::MutTy {
1478                             mutbl: mut_ty.mutbl,
1479                             ty: build_to(mut_ty.ty, to),
1480                         })
1481                     }
1482                     hir::TyPtr(mut_ty) => {
1483                         hir::TyPtr(hir::MutTy {
1484                             mutbl: mut_ty.mutbl,
1485                             ty: build_to(mut_ty.ty, to),
1486                         })
1487                     }
1488                     hir::TyVec(ty) => hir::TyVec(build_to(ty, to)),
1489                     hir::TyFixedLengthVec(ty, e) => {
1490                         hir::TyFixedLengthVec(build_to(ty, to), e)
1491                     }
1492                     hir::TyTup(tys) => {
1493                         hir::TyTup(tys.into_iter().map(|ty| build_to(ty, to)).collect())
1494                     }
1495                     other => other
1496                 };
1497                 hir::Ty { id: id, node: new_node, span: span }
1498             })
1499         }
1500
1501         build_to(from, &mut Some(to))
1502     }
1503
1504     fn rebuild_path(&self,
1505                     rebuild_info: RebuildPathInfo,
1506                     lifetime: hir::Lifetime)
1507                     -> hir::Path
1508     {
1509         let RebuildPathInfo {
1510             path,
1511             indexes,
1512             expected,
1513             anon_nums,
1514             region_names,
1515         } = rebuild_info;
1516
1517         let last_seg = path.segments.last().unwrap();
1518         let new_parameters = match last_seg.parameters {
1519             hir::ParenthesizedParameters(..) => {
1520                 last_seg.parameters.clone()
1521             }
1522
1523             hir::AngleBracketedParameters(ref data) => {
1524                 let mut new_lts = Vec::new();
1525                 if data.lifetimes.is_empty() {
1526                     // traverse once to see if there's a need to insert lifetime
1527                     let need_insert = (0..expected).any(|i| {
1528                         indexes.contains(&i)
1529                     });
1530                     if need_insert {
1531                         for i in 0..expected {
1532                             if indexes.contains(&i) {
1533                                 new_lts.push(lifetime);
1534                             } else {
1535                                 new_lts.push(self.life_giver.give_lifetime());
1536                             }
1537                         }
1538                     }
1539                 } else {
1540                     for (i, lt) in data.lifetimes.iter().enumerate() {
1541                         if indexes.contains(&(i as u32)) {
1542                             new_lts.push(lifetime);
1543                         } else {
1544                             new_lts.push(*lt);
1545                         }
1546                     }
1547                 }
1548                 let new_types = data.types.iter().map(|t| {
1549                     self.rebuild_arg_ty_or_output(&**t, lifetime, anon_nums, region_names)
1550                 }).collect();
1551                 let new_bindings = data.bindings.iter().map(|b| {
1552                     hir::TypeBinding {
1553                         id: b.id,
1554                         name: b.name,
1555                         ty: self.rebuild_arg_ty_or_output(&*b.ty,
1556                                                           lifetime,
1557                                                           anon_nums,
1558                                                           region_names),
1559                         span: b.span
1560                     }
1561                 }).collect();
1562                 hir::AngleBracketedParameters(hir::AngleBracketedParameterData {
1563                     lifetimes: new_lts.into(),
1564                     types: new_types,
1565                     bindings: new_bindings,
1566                })
1567             }
1568         };
1569         let new_seg = hir::PathSegment {
1570             identifier: last_seg.identifier,
1571             parameters: new_parameters
1572         };
1573         let mut new_segs = Vec::new();
1574         new_segs.extend_from_slice(path.segments.split_last().unwrap().1);
1575         new_segs.push(new_seg);
1576         hir::Path {
1577             span: path.span,
1578             global: path.global,
1579             segments: new_segs.into()
1580         }
1581     }
1582 }
1583
1584 impl<'a, 'tcx> ErrorReportingHelpers<'tcx> for InferCtxt<'a, 'tcx> {
1585     fn give_expl_lifetime_param(&self,
1586                                 err: &mut DiagnosticBuilder,
1587                                 decl: &hir::FnDecl,
1588                                 unsafety: hir::Unsafety,
1589                                 constness: hir::Constness,
1590                                 name: ast::Name,
1591                                 opt_explicit_self: Option<&hir::ExplicitSelf_>,
1592                                 generics: &hir::Generics,
1593                                 span: Span) {
1594         let suggested_fn = pprust::fun_to_string(decl, unsafety, constness, name,
1595                                                  opt_explicit_self, generics);
1596         let msg = format!("consider using an explicit lifetime \
1597                            parameter as shown: {}", suggested_fn);
1598         err.span_help(span, &msg[..]);
1599     }
1600
1601     fn report_inference_failure(&self,
1602                                 var_origin: RegionVariableOrigin)
1603                                 -> DiagnosticBuilder<'tcx> {
1604         let br_string = |br: ty::BoundRegion| {
1605             let mut s = br.to_string();
1606             if !s.is_empty() {
1607                 s.push_str(" ");
1608             }
1609             s
1610         };
1611         let var_description = match var_origin {
1612             infer::MiscVariable(_) => "".to_string(),
1613             infer::PatternRegion(_) => " for pattern".to_string(),
1614             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
1615             infer::Autoref(_) => " for autoref".to_string(),
1616             infer::Coercion(_) => " for automatic coercion".to_string(),
1617             infer::LateBoundRegion(_, br, infer::FnCall) => {
1618                 format!(" for lifetime parameter {}in function call",
1619                         br_string(br))
1620             }
1621             infer::LateBoundRegion(_, br, infer::HigherRankedType) => {
1622                 format!(" for lifetime parameter {}in generic type", br_string(br))
1623             }
1624             infer::LateBoundRegion(_, br, infer::AssocTypeProjection(type_name)) => {
1625                 format!(" for lifetime parameter {}in trait containing associated type `{}`",
1626                         br_string(br), type_name)
1627             }
1628             infer::EarlyBoundRegion(_, name) => {
1629                 format!(" for lifetime parameter `{}`",
1630                         name)
1631             }
1632             infer::BoundRegionInCoherence(name) => {
1633                 format!(" for lifetime parameter `{}` in coherence check",
1634                         name)
1635             }
1636             infer::UpvarRegion(ref upvar_id, _) => {
1637                 format!(" for capture of `{}` by closure",
1638                         self.tcx.local_var_name_str(upvar_id.var_id).to_string())
1639             }
1640         };
1641
1642         struct_span_err!(self.tcx.sess, var_origin.span(), E0495,
1643                   "cannot infer an appropriate lifetime{} \
1644                    due to conflicting requirements",
1645                   var_description)
1646     }
1647
1648     fn note_region_origin(&self, err: &mut DiagnosticBuilder, origin: &SubregionOrigin<'tcx>) {
1649         match *origin {
1650             infer::Subtype(ref trace) => {
1651                 let desc = match trace.origin {
1652                     TypeOrigin::Misc(_) => {
1653                         "types are compatible"
1654                     }
1655                     TypeOrigin::MethodCompatCheck(_) => {
1656                         "method type is compatible with trait"
1657                     }
1658                     TypeOrigin::ExprAssignable(_) => {
1659                         "expression is assignable"
1660                     }
1661                     TypeOrigin::RelateTraitRefs(_) => {
1662                         "traits are compatible"
1663                     }
1664                     TypeOrigin::RelateSelfType(_) => {
1665                         "self type matches impl self type"
1666                     }
1667                     TypeOrigin::RelateOutputImplTypes(_) => {
1668                         "trait type parameters matches those \
1669                                  specified on the impl"
1670                     }
1671                     TypeOrigin::MatchExpressionArm(_, _, _) => {
1672                         "match arms have compatible types"
1673                     }
1674                     TypeOrigin::IfExpression(_) => {
1675                         "if and else have compatible types"
1676                     }
1677                     TypeOrigin::IfExpressionWithNoElse(_) => {
1678                         "if may be missing an else clause"
1679                     }
1680                     TypeOrigin::RangeExpression(_) => {
1681                         "start and end of range have compatible types"
1682                     }
1683                     TypeOrigin::EquatePredicate(_) => {
1684                         "equality where clause is satisfied"
1685                     }
1686                 };
1687
1688                 match self.values_str(&trace.values) {
1689                     Some(values_str) => {
1690                         err.span_note(
1691                             trace.origin.span(),
1692                             &format!("...so that {} ({})",
1693                                     desc, values_str));
1694                     }
1695                     None => {
1696                         // Really should avoid printing this error at
1697                         // all, since it is derived, but that would
1698                         // require more refactoring than I feel like
1699                         // doing right now. - nmatsakis
1700                         err.span_note(
1701                             trace.origin.span(),
1702                             &format!("...so that {}", desc));
1703                     }
1704                 }
1705             }
1706             infer::Reborrow(span) => {
1707                 err.span_note(
1708                     span,
1709                     "...so that reference does not outlive \
1710                     borrowed content");
1711             }
1712             infer::ReborrowUpvar(span, ref upvar_id) => {
1713                 err.span_note(
1714                     span,
1715                     &format!(
1716                         "...so that closure can access `{}`",
1717                         self.tcx.local_var_name_str(upvar_id.var_id)
1718                             .to_string()));
1719             }
1720             infer::InfStackClosure(span) => {
1721                 err.span_note(
1722                     span,
1723                     "...so that closure does not outlive its stack frame");
1724             }
1725             infer::InvokeClosure(span) => {
1726                 err.span_note(
1727                     span,
1728                     "...so that closure is not invoked outside its lifetime");
1729             }
1730             infer::DerefPointer(span) => {
1731                 err.span_note(
1732                     span,
1733                     "...so that pointer is not dereferenced \
1734                     outside its lifetime");
1735             }
1736             infer::FreeVariable(span, id) => {
1737                 err.span_note(
1738                     span,
1739                     &format!("...so that captured variable `{}` \
1740                             does not outlive the enclosing closure",
1741                             self.tcx.local_var_name_str(id)));
1742             }
1743             infer::IndexSlice(span) => {
1744                 err.span_note(
1745                     span,
1746                     "...so that slice is not indexed outside the lifetime");
1747             }
1748             infer::RelateObjectBound(span) => {
1749                 err.span_note(
1750                     span,
1751                     "...so that it can be closed over into an object");
1752             }
1753             infer::CallRcvr(span) => {
1754                 err.span_note(
1755                     span,
1756                     "...so that method receiver is valid for the method call");
1757             }
1758             infer::CallArg(span) => {
1759                 err.span_note(
1760                     span,
1761                     "...so that argument is valid for the call");
1762             }
1763             infer::CallReturn(span) => {
1764                 err.span_note(
1765                     span,
1766                     "...so that return value is valid for the call");
1767             }
1768             infer::Operand(span) => {
1769                 err.span_note(
1770                     span,
1771                     "...so that operand is valid for operation");
1772             }
1773             infer::AddrOf(span) => {
1774                 err.span_note(
1775                     span,
1776                     "...so that reference is valid \
1777                      at the time of borrow");
1778             }
1779             infer::AutoBorrow(span) => {
1780                 err.span_note(
1781                     span,
1782                     "...so that auto-reference is valid \
1783                      at the time of borrow");
1784             }
1785             infer::ExprTypeIsNotInScope(t, span) => {
1786                 err.span_note(
1787                     span,
1788                     &format!("...so type `{}` of expression is valid during the \
1789                              expression",
1790                             self.ty_to_string(t)));
1791             }
1792             infer::BindingTypeIsNotValidAtDecl(span) => {
1793                 err.span_note(
1794                     span,
1795                     "...so that variable is valid at time of its declaration");
1796             }
1797             infer::ParameterInScope(_, span) => {
1798                 err.span_note(
1799                     span,
1800                     "...so that a type/lifetime parameter is in scope here");
1801             }
1802             infer::DataBorrowed(ty, span) => {
1803                 err.span_note(
1804                     span,
1805                     &format!("...so that the type `{}` is not borrowed for too long",
1806                              self.ty_to_string(ty)));
1807             }
1808             infer::ReferenceOutlivesReferent(ty, span) => {
1809                 err.span_note(
1810                     span,
1811                     &format!("...so that the reference type `{}` \
1812                              does not outlive the data it points at",
1813                             self.ty_to_string(ty)));
1814             }
1815             infer::RelateParamBound(span, t) => {
1816                 err.span_note(
1817                     span,
1818                     &format!("...so that the type `{}` \
1819                              will meet its required lifetime bounds",
1820                             self.ty_to_string(t)));
1821             }
1822             infer::RelateDefaultParamBound(span, t) => {
1823                 err.span_note(
1824                     span,
1825                     &format!("...so that type parameter \
1826                              instantiated with `{}`, \
1827                              will meet its declared lifetime bounds",
1828                             self.ty_to_string(t)));
1829             }
1830             infer::RelateRegionParamBound(span) => {
1831                 err.span_note(
1832                     span,
1833                     "...so that the declared lifetime parameter bounds \
1834                                 are satisfied");
1835             }
1836             infer::SafeDestructor(span) => {
1837                 err.span_note(
1838                     span,
1839                     "...so that references are valid when the destructor \
1840                      runs");
1841             }
1842         }
1843     }
1844 }
1845
1846 pub trait Resolvable<'tcx> {
1847     fn resolve<'a>(&self, infcx: &InferCtxt<'a, 'tcx>) -> Self;
1848 }
1849
1850 impl<'tcx> Resolvable<'tcx> for Ty<'tcx> {
1851     fn resolve<'a>(&self, infcx: &InferCtxt<'a, 'tcx>) -> Ty<'tcx> {
1852         infcx.resolve_type_vars_if_possible(self)
1853     }
1854 }
1855
1856 impl<'tcx> Resolvable<'tcx> for ty::TraitRef<'tcx> {
1857     fn resolve<'a>(&self, infcx: &InferCtxt<'a, 'tcx>)
1858                    -> ty::TraitRef<'tcx> {
1859         infcx.resolve_type_vars_if_possible(self)
1860     }
1861 }
1862
1863 impl<'tcx> Resolvable<'tcx> for ty::PolyTraitRef<'tcx> {
1864     fn resolve<'a>(&self,
1865                    infcx: &InferCtxt<'a, 'tcx>)
1866                    -> ty::PolyTraitRef<'tcx>
1867     {
1868         infcx.resolve_type_vars_if_possible(self)
1869     }
1870 }
1871
1872 fn lifetimes_in_scope(tcx: &ty::ctxt,
1873                       scope_id: ast::NodeId)
1874                       -> Vec<hir::LifetimeDef> {
1875     let mut taken = Vec::new();
1876     let parent = tcx.map.get_parent(scope_id);
1877     let method_id_opt = match tcx.map.find(parent) {
1878         Some(node) => match node {
1879             ast_map::NodeItem(item) => match item.node {
1880                 hir::ItemFn(_, _, _, _, ref gen, _) => {
1881                     taken.extend_from_slice(&gen.lifetimes);
1882                     None
1883                 },
1884                 _ => None
1885             },
1886             ast_map::NodeImplItem(ii) => {
1887                 match ii.node {
1888                     hir::ImplItemKind::Method(ref sig, _) => {
1889                         taken.extend_from_slice(&sig.generics.lifetimes);
1890                         Some(ii.id)
1891                     }
1892                     _ => None,
1893                 }
1894             }
1895             _ => None
1896         },
1897         None => None
1898     };
1899     if method_id_opt.is_some() {
1900         let method_id = method_id_opt.unwrap();
1901         let parent = tcx.map.get_parent(method_id);
1902         match tcx.map.find(parent) {
1903             Some(node) => match node {
1904                 ast_map::NodeItem(item) => match item.node {
1905                     hir::ItemImpl(_, _, ref gen, _, _, _) => {
1906                         taken.extend_from_slice(&gen.lifetimes);
1907                     }
1908                     _ => ()
1909                 },
1910                 _ => ()
1911             },
1912             None => ()
1913         }
1914     }
1915     return taken;
1916 }
1917
1918 // LifeGiver is responsible for generating fresh lifetime names
1919 struct LifeGiver {
1920     taken: HashSet<String>,
1921     counter: Cell<usize>,
1922     generated: RefCell<Vec<hir::Lifetime>>,
1923 }
1924
1925 impl LifeGiver {
1926     fn with_taken(taken: &[hir::LifetimeDef]) -> LifeGiver {
1927         let mut taken_ = HashSet::new();
1928         for lt in taken {
1929             let lt_name = lt.lifetime.name.to_string();
1930             taken_.insert(lt_name);
1931         }
1932         LifeGiver {
1933             taken: taken_,
1934             counter: Cell::new(0),
1935             generated: RefCell::new(Vec::new()),
1936         }
1937     }
1938
1939     fn inc_counter(&self) {
1940         let c = self.counter.get();
1941         self.counter.set(c+1);
1942     }
1943
1944     fn give_lifetime(&self) -> hir::Lifetime {
1945         let lifetime;
1946         loop {
1947             let mut s = String::from("'");
1948             s.push_str(&num_to_string(self.counter.get()));
1949             if !self.taken.contains(&s) {
1950                 lifetime = name_to_dummy_lifetime(token::intern(&s[..]));
1951                 self.generated.borrow_mut().push(lifetime);
1952                 break;
1953             }
1954             self.inc_counter();
1955         }
1956         self.inc_counter();
1957         return lifetime;
1958
1959         // 0 .. 25 generates a .. z, 26 .. 51 generates aa .. zz, and so on
1960         fn num_to_string(counter: usize) -> String {
1961             let mut s = String::new();
1962             let (n, r) = (counter/26 + 1, counter % 26);
1963             let letter: char = from_u32((r+97) as u32).unwrap();
1964             for _ in 0..n {
1965                 s.push(letter);
1966             }
1967             s
1968         }
1969     }
1970
1971     fn get_generated_lifetimes(&self) -> Vec<hir::Lifetime> {
1972         self.generated.borrow().clone()
1973     }
1974 }
1975
1976 fn name_to_dummy_lifetime(name: ast::Name) -> hir::Lifetime {
1977     hir::Lifetime { id: ast::DUMMY_NODE_ID,
1978                     span: codemap::DUMMY_SP,
1979                     name: name }
1980 }