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