src/librustc_borrowck/borrowck/mod.rs

   1 // Copyright 2012-2014 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 //! See The Book chapter on the borrow checker for more details.
  12
  13 #![allow(non_camel_case_types)]
  14
  15 pub use self::LoanPathKind::*;
  16 pub use self::LoanPathElem::*;
  17 pub use self::bckerr_code::*;
  18 pub use self::AliasableViolationKind::*;
  19 pub use self::MovedValueUseKind::*;
  20
  21 use self::InteriorKind::*;
  22
  23 use rustc::hir::map as hir_map;
  24 use rustc::hir::map::blocks::FnLikeNode;
  25 use rustc::cfg;
  26 use rustc::middle::dataflow::DataFlowContext;
  27 use rustc::middle::dataflow::BitwiseOperator;
  28 use rustc::middle::dataflow::DataFlowOperator;
  29 use rustc::middle::dataflow::KillFrom;
  30 use rustc::hir::def_id::{DefId, DefIndex};
  31 use rustc::middle::expr_use_visitor as euv;
  32 use rustc::middle::mem_categorization as mc;
  33 use rustc::middle::mem_categorization::Categorization;
  34 use rustc::middle::mem_categorization::ImmutabilityBlame;
  35 use rustc::middle::region::{self, RegionMaps};
  36 use rustc::middle::free_region::RegionRelations;
  37 use rustc::ty::{self, TyCtxt};
  38 use rustc::ty::maps::Providers;
  39
  40 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  41
  42 use std::fmt;
  43 use std::rc::Rc;
  44 use std::hash::{Hash, Hasher};
  45 use syntax::ast;
  46 use syntax_pos::{MultiSpan, Span};
  47 use errors::DiagnosticBuilder;
  48
  49 use rustc::hir;
  50 use rustc::hir::intravisit::{self, Visitor};
  51
  52 pub mod check_loans;
  53
  54 pub mod gather_loans;
  55
  56 pub mod move_data;
  57
  58 #[derive(Clone, Copy)]
  59 pub struct LoanDataFlowOperator;
  60
  61 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  62
  63 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  64     for body_owner_def_id in tcx.body_owners() {
  65         tcx.borrowck(body_owner_def_id);
  66     }
  67 }
  68
  69 pub fn provide(providers: &mut Providers) {
  70     *providers = Providers {
  71         borrowck,
  72         ..*providers
  73     };
  74 }
  75
  76 /// Collection of conclusions determined via borrow checker analyses.
  77 pub struct AnalysisData<'a, 'tcx: 'a> {
  78     pub all_loans: Vec<Loan<'tcx>>,
  79     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  80     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  81 }
  82
  83 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId) {
  84     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  85
  86     let owner_id = tcx.hir.as_local_node_id(owner_def_id).unwrap();
  87
  88     match tcx.hir.get(owner_id) {
  89         hir_map::NodeStructCtor(_) |
  90         hir_map::NodeVariant(_) => {
  91             // We get invoked with anything that has MIR, but some of
  92             // those things (notably the synthesized constructors from
  93             // tuple structs/variants) do not have an associated body
  94             // and do not need borrowchecking.
  95             return;
  96         }
  97         _ => { }
  98     }
  99
 100     let body_id = tcx.hir.body_owned_by(owner_id);
 101     let tables = tcx.typeck_tables_of(owner_def_id);
 102     let region_maps = tcx.region_maps(owner_def_id);
 103     let bccx = &mut BorrowckCtxt { tcx, tables, region_maps, owner_def_id };
 104
 105     let body = bccx.tcx.hir.body(body_id);
 106
 107     // Eventually, borrowck will always read the MIR, but at the
 108     // moment we do not. So, for now, we always force MIR to be
 109     // constructed for a given fn, since this may result in errors
 110     // being reported and we want that to happen.
 111     //
 112     // Note that `mir_validated` is a "stealable" result; the
 113     // thief, `optimized_mir()`, forces borrowck, so we know that
 114     // is not yet stolen.
 115     tcx.mir_validated(owner_def_id).borrow();
 116
 117     // option dance because you can't capture an uninitialized variable
 118     // by mut-ref.
 119     let mut cfg = None;
 120     if let Some(AnalysisData { all_loans,
 121                                loans: loan_dfcx,
 122                                move_data: flowed_moves }) =
 123         build_borrowck_dataflow_data(bccx, false, body_id,
 124                                      |bccx| {
 125                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 126                                          cfg.as_mut().unwrap()
 127                                      })
 128     {
 129         check_loans::check_loans(bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 130     }
 131 }
 132
 133 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 134                                                  force_analysis: bool,
 135                                                  body_id: hir::BodyId,
 136                                                  get_cfg: F)
 137                                                  -> Option<AnalysisData<'a, 'tcx>>
 138     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 139 {
 140     // Check the body of fn items.
 141     let tcx = this.tcx;
 142     let body = tcx.hir.body(body_id);
 143     let id_range = {
 144         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 145         visitor.visit_body(body);
 146         visitor.result()
 147     };
 148     let (all_loans, move_data) =
 149         gather_loans::gather_loans_in_fn(this, body_id);
 150
 151     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 152         // large arrays of data inserted as constants can take a lot of
 153         // time and memory to borrow-check - see issue #36799. However,
 154         // they don't have lvalues, so no borrow-check is actually needed.
 155         // Recognize that case and skip borrow-checking.
 156         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 157         return None;
 158     } else {
 159         debug!("propagating loans in {:?}", body_id);
 160     }
 161
 162     let cfg = get_cfg(this);
 163     let mut loan_dfcx =
 164         DataFlowContext::new(this.tcx,
 165                              "borrowck",
 166                              Some(body),
 167                              cfg,
 168                              LoanDataFlowOperator,
 169                              id_range,
 170                              all_loans.len());
 171     for (loan_idx, loan) in all_loans.iter().enumerate() {
 172         loan_dfcx.add_gen(loan.gen_scope.node_id(), loan_idx);
 173         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 174                            loan.kill_scope.node_id(), loan_idx);
 175     }
 176     loan_dfcx.add_kills_from_flow_exits(cfg);
 177     loan_dfcx.propagate(cfg, body);
 178
 179     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 180                                                       this,
 181                                                       cfg,
 182                                                       id_range,
 183                                                       body);
 184
 185     Some(AnalysisData { all_loans,
 186                         loans: loan_dfcx,
 187                         move_data:flowed_moves })
 188 }
 189
 190 /// Accessor for introspective clients inspecting `AnalysisData` and
 191 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 192 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 193     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 194     body_id: hir::BodyId,
 195     cfg: &cfg::CFG)
 196     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 197 {
 198     let owner_id = tcx.hir.body_owner(body_id);
 199     let owner_def_id = tcx.hir.local_def_id(owner_id);
 200     let tables = tcx.typeck_tables_of(owner_def_id);
 201     let region_maps = tcx.region_maps(owner_def_id);
 202     let mut bccx = BorrowckCtxt { tcx, tables, region_maps, owner_def_id };
 203
 204     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 205     (bccx, dataflow_data.unwrap())
 206 }
 207
 208 // ----------------------------------------------------------------------
 209 // Type definitions
 210
 211 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 212     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 213
 214     // tables for the current thing we are checking; set to
 215     // Some in `borrowck_fn` and cleared later
 216     tables: &'a ty::TypeckTables<'tcx>,
 217
 218     region_maps: Rc<RegionMaps>,
 219
 220     owner_def_id: DefId,
 221 }
 222
 223 impl<'b, 'tcx: 'b> BorrowckErrors for BorrowckCtxt<'b, 'tcx> {
 224     fn struct_span_err_with_code<'a, S: Into<MultiSpan>>(&'a self,
 225                                                          sp: S,
 226                                                          msg: &str,
 227                                                          code: &str)
 228                                                          -> DiagnosticBuilder<'a>
 229     {
 230         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 231     }
 232
 233     fn struct_span_err<'a, S: Into<MultiSpan>>(&'a self,
 234                                                sp: S,
 235                                                msg: &str)
 236                                                -> DiagnosticBuilder<'a>
 237     {
 238         self.tcx.sess.struct_span_err(sp, msg)
 239     }
 240 }
 241
 242 ///////////////////////////////////////////////////////////////////////////
 243 // Loans and loan paths
 244
 245 /// Record of a loan that was issued.
 246 pub struct Loan<'tcx> {
 247     index: usize,
 248     loan_path: Rc<LoanPath<'tcx>>,
 249     kind: ty::BorrowKind,
 250     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 251
 252     /// gen_scope indicates where loan is introduced. Typically the
 253     /// loan is introduced at the point of the borrow, but in some
 254     /// cases, notably method arguments, the loan may be introduced
 255     /// only later, once it comes into scope.  See also
 256     /// `GatherLoanCtxt::compute_gen_scope`.
 257     gen_scope: region::CodeExtent,
 258
 259     /// kill_scope indicates when the loan goes out of scope.  This is
 260     /// either when the lifetime expires or when the local variable
 261     /// which roots the loan-path goes out of scope, whichever happens
 262     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 263     kill_scope: region::CodeExtent,
 264     span: Span,
 265     cause: euv::LoanCause,
 266 }
 267
 268 impl<'tcx> Loan<'tcx> {
 269     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 270         self.loan_path.clone()
 271     }
 272 }
 273
 274 #[derive(Eq)]
 275 pub struct LoanPath<'tcx> {
 276     kind: LoanPathKind<'tcx>,
 277     ty: ty::Ty<'tcx>,
 278 }
 279
 280 impl<'tcx> PartialEq for LoanPath<'tcx> {
 281     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 282         self.kind == that.kind
 283     }
 284 }
 285
 286 impl<'tcx> Hash for LoanPath<'tcx> {
 287     fn hash<H: Hasher>(&self, state: &mut H) {
 288         self.kind.hash(state);
 289     }
 290 }
 291
 292 #[derive(PartialEq, Eq, Hash, Debug)]
 293 pub enum LoanPathKind<'tcx> {
 294     LpVar(ast::NodeId),                         // `x` in README.md
 295     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 296     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 297     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 298 }
 299
 300 impl<'tcx> LoanPath<'tcx> {
 301     fn new(kind: LoanPathKind<'tcx>, ty: ty::Ty<'tcx>) -> LoanPath<'tcx> {
 302         LoanPath { kind: kind, ty: ty }
 303     }
 304
 305     fn to_type(&self) -> ty::Ty<'tcx> { self.ty }
 306 }
 307
 308 // FIXME (pnkfelix): See discussion here
 309 // https://github.com/pnkfelix/rust/commit/
 310 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 311 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 312
 313 // A local, "cleaned" version of `mc::InteriorKind` that drops
 314 // information that is not relevant to loan-path analysis. (In
 315 // particular, the distinction between how precisely an array-element
 316 // is tracked is irrelevant here.)
 317 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 318 pub enum InteriorKind {
 319     InteriorField(mc::FieldName),
 320     InteriorElement,
 321 }
 322
 323 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 324 impl ToInteriorKind for mc::InteriorKind {
 325     fn cleaned(self) -> InteriorKind {
 326         match self {
 327             mc::InteriorField(name) => InteriorField(name),
 328             mc::InteriorElement(_) => InteriorElement,
 329         }
 330     }
 331 }
 332
 333 // This can be:
 334 // - a pointer dereference (`*LV` in README.md)
 335 // - a field reference, with an optional definition of the containing
 336 //   enum variant (`LV.f` in README.md)
 337 // `DefId` is present when the field is part of struct that is in
 338 // a variant of an enum. For instance in:
 339 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 340 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 341 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 342 pub enum LoanPathElem<'tcx> {
 343     LpDeref(mc::PointerKind<'tcx>),
 344     LpInterior(Option<DefId>, InteriorKind),
 345 }
 346
 347 fn closure_to_block(closure_id: DefIndex,
 348                     tcx: TyCtxt) -> ast::NodeId {
 349     let closure_id = tcx.hir.def_index_to_node_id(closure_id);
 350     match tcx.hir.get(closure_id) {
 351         hir_map::NodeExpr(expr) => match expr.node {
 352             hir::ExprClosure(.., body_id, _) => {
 353                 body_id.node_id
 354             }
 355             _ => {
 356                 bug!("encountered non-closure id: {}", closure_id)
 357             }
 358         },
 359         _ => bug!("encountered non-expr id: {}", closure_id)
 360     }
 361 }
 362
 363 impl<'a, 'tcx> LoanPath<'tcx> {
 364     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::CodeExtent {
 365         match self.kind {
 366             LpVar(local_id) => bccx.region_maps.var_scope(local_id),
 367             LpUpvar(upvar_id) => {
 368                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 369                 region::CodeExtent::Misc(block_id)
 370             }
 371             LpDowncast(ref base, _) |
 372             LpExtend(ref base, ..) => base.kill_scope(bccx),
 373         }
 374     }
 375
 376     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 377         match (&self.kind, &other.kind) {
 378             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 379              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 380                 if id == id2 && opt_variant_id == opt_variant_id2 {
 381                     base.has_fork(&base2)
 382                 } else {
 383                     true
 384                 },
 385             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 386             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 387             _ => false,
 388         }
 389     }
 390
 391     fn depth(&self) -> usize {
 392         match self.kind {
 393             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 394             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 395             _ => 0,
 396         }
 397     }
 398
 399     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 400         match (&self.kind, &other.kind) {
 401             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 402              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 403                 if id == id2 && opt_variant_id == opt_variant_id2 {
 404                     base.common(&base2).map(|x| {
 405                         let xd = x.depth();
 406                         if base.depth() == xd && base2.depth() == xd {
 407                             LoanPath {
 408                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 409                                 ty: self.ty,
 410                             }
 411                         } else {
 412                             x
 413                         }
 414                     })
 415                 } else {
 416                     base.common(&base2)
 417                 }
 418             }
 419             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 420             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 421             (&LpVar(id), &LpVar(id2)) => {
 422                 if id == id2 {
 423                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 424                 } else {
 425                     None
 426                 }
 427             }
 428             (&LpUpvar(id), &LpUpvar(id2)) => {
 429                 if id == id2 {
 430                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 431                 } else {
 432                     None
 433                 }
 434             }
 435             _ => None,
 436         }
 437     }
 438 }
 439
 440 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 441     //! Computes the `LoanPath` (if any) for a `cmt`.
 442     //! Note that this logic is somewhat duplicated in
 443     //! the method `compute()` found in `gather_loans::restrictions`,
 444     //! which allows it to share common loan path pieces as it
 445     //! traverses the CMT.
 446
 447     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 448
 449     match cmt.cat {
 450         Categorization::Rvalue(..) |
 451         Categorization::StaticItem => {
 452             None
 453         }
 454
 455         Categorization::Local(id) => {
 456             Some(new_lp(LpVar(id)))
 457         }
 458
 459         Categorization::Upvar(mc::Upvar { id, .. }) => {
 460             Some(new_lp(LpUpvar(id)))
 461         }
 462
 463         Categorization::Deref(ref cmt_base, pk) => {
 464             opt_loan_path(cmt_base).map(|lp| {
 465                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 466             })
 467         }
 468
 469         Categorization::Interior(ref cmt_base, ik) => {
 470             opt_loan_path(cmt_base).map(|lp| {
 471                 let opt_variant_id = match cmt_base.cat {
 472                     Categorization::Downcast(_, did) =>  Some(did),
 473                     _ => None
 474                 };
 475                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 476             })
 477         }
 478
 479         Categorization::Downcast(ref cmt_base, variant_def_id) =>
 480             opt_loan_path(cmt_base)
 481             .map(|lp| {
 482                 new_lp(LpDowncast(lp, variant_def_id))
 483             }),
 484
 485     }
 486 }
 487
 488 ///////////////////////////////////////////////////////////////////////////
 489 // Errors
 490
 491 // Errors that can occur
 492 #[derive(Debug, PartialEq)]
 493 pub enum bckerr_code<'tcx> {
 494     err_mutbl,
 495     /// superscope, subscope, loan cause
 496     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 497     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 498 }
 499
 500 // Combination of an error code and the categorization of the expression
 501 // that caused it
 502 #[derive(Debug, PartialEq)]
 503 pub struct BckError<'tcx> {
 504     span: Span,
 505     cause: AliasableViolationKind,
 506     cmt: mc::cmt<'tcx>,
 507     code: bckerr_code<'tcx>
 508 }
 509
 510 #[derive(Copy, Clone, Debug, PartialEq)]
 511 pub enum AliasableViolationKind {
 512     MutabilityViolation,
 513     BorrowViolation(euv::LoanCause)
 514 }
 515
 516 #[derive(Copy, Clone, Debug)]
 517 pub enum MovedValueUseKind {
 518     MovedInUse,
 519     MovedInCapture,
 520 }
 521
 522 ///////////////////////////////////////////////////////////////////////////
 523 // Misc
 524
 525 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 526     pub fn is_subregion_of(&self,
 527                            r_sub: ty::Region<'tcx>,
 528                            r_sup: ty::Region<'tcx>)
 529                            -> bool
 530     {
 531         let region_rels = RegionRelations::new(self.tcx,
 532                                                self.owner_def_id,
 533                                                &self.region_maps,
 534                                                &self.tables.free_region_map);
 535         region_rels.is_subregion_of(r_sub, r_sup)
 536     }
 537
 538     pub fn report(&self, err: BckError<'tcx>) {
 539         // Catch and handle some particular cases.
 540         match (&err.code, &err.cause) {
 541             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 542              &BorrowViolation(euv::ClosureCapture(span))) |
 543             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 544              &BorrowViolation(euv::ClosureCapture(span))) |
 545             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 546              &BorrowViolation(euv::ClosureCapture(span))) => {
 547                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 548             }
 549             _ => { }
 550         }
 551
 552         let mut db = self.bckerr_to_diag(&err);
 553         self.note_and_explain_bckerr(&mut db, err);
 554         db.emit();
 555     }
 556
 557     pub fn report_use_of_moved_value(&self,
 558                                      use_span: Span,
 559                                      use_kind: MovedValueUseKind,
 560                                      lp: &LoanPath<'tcx>,
 561                                      the_move: &move_data::Move,
 562                                      moved_lp: &LoanPath<'tcx>,
 563                                      _param_env: ty::ParamEnv<'tcx>) {
 564         let (verb, verb_participle) = match use_kind {
 565             MovedInUse => ("use", "used"),
 566             MovedInCapture => ("capture", "captured"),
 567         };
 568
 569         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 570             move_data::Declared => {
 571                 // If this is an uninitialized variable, just emit a simple warning
 572                 // and return.
 573                 self.cannot_act_on_uninitialized_variable(use_span,
 574                                                           verb,
 575                                                           &self.loan_path_to_string(lp),
 576                                                           Origin::Ast)
 577                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 578                                                   self.loan_path_to_string(lp)))
 579                     .emit();
 580                 return;
 581             }
 582             _ => {
 583                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 584                 // normally generate a rather confusing message:
 585                 //
 586                 //     error: use of moved value: `x.b`
 587                 //     note: `x.a` moved here...
 588                 //
 589                 // What we want to do instead is get the 'common ancestor' of the two moves and
 590                 // use that for most of the message instead, giving is something like this:
 591                 //
 592                 //     error: use of moved value: `x`
 593                 //     note: `x` moved here (through moving `x.a`)...
 594
 595                 let common = moved_lp.common(lp);
 596                 let has_common = common.is_some();
 597                 let has_fork = moved_lp.has_fork(lp);
 598                 let (nl, ol, moved_lp_msg) =
 599                     if has_fork && has_common {
 600                         let nl = self.loan_path_to_string(&common.unwrap());
 601                         let ol = nl.clone();
 602                         let moved_lp_msg = format!(" (through moving `{}`)",
 603                                                    self.loan_path_to_string(moved_lp));
 604                         (nl, ol, moved_lp_msg)
 605                     } else {
 606                         (self.loan_path_to_string(lp),
 607                          self.loan_path_to_string(moved_lp),
 608                          String::new())
 609                     };
 610
 611                 let partial = moved_lp.depth() > lp.depth();
 612                 let msg = if !has_fork && partial { "partially " }
 613                           else if has_fork && !has_common { "collaterally "}
 614                           else { "" };
 615                 let mut err = struct_span_err!(
 616                     self.tcx.sess, use_span, E0382,
 617                     "{} of {}moved value: `{}`",
 618                     verb, msg, nl);
 619                 let need_note = match lp.ty.sty {
 620                     ty::TypeVariants::TyClosure(id, _) => {
 621                         let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
 622                         let hir_id = self.tcx.hir.node_to_hir_id(node_id);
 623                         if let Some(&(ty::ClosureKind::FnOnce, Some((span, name)))) =
 624                             self.tables.closure_kinds().get(hir_id)
 625                         {
 626                             err.span_note(span, &format!(
 627                                 "closure cannot be invoked more than once because \
 628                                 it moves the variable `{}` out of its environment",
 629                                 name
 630                             ));
 631                             false
 632                         } else {
 633                             true
 634                         }
 635                     }
 636                     _ => true,
 637                 };
 638                 (ol, moved_lp_msg, err, need_note)
 639             }
 640         };
 641
 642         // Get type of value and span where it was previously
 643         // moved.
 644         let (move_span, move_note) = match the_move.kind {
 645             move_data::Declared => {
 646                 unreachable!();
 647             }
 648
 649             move_data::MoveExpr |
 650             move_data::MovePat =>
 651                 (self.tcx.hir.span(the_move.id), ""),
 652
 653             move_data::Captured =>
 654                 (match self.tcx.hir.expect_expr(the_move.id).node {
 655                     hir::ExprClosure(.., fn_decl_span) => fn_decl_span,
 656                     ref r => bug!("Captured({}) maps to non-closure: {:?}",
 657                                   the_move.id, r),
 658                 }, " (into closure)"),
 659         };
 660
 661         // Annotate the use and the move in the span. Watch out for
 662         // the case where the use and the move are the same. This
 663         // means the use is in a loop.
 664         err = if use_span == move_span {
 665             err.span_label(
 666                 use_span,
 667                 format!("value moved{} here in previous iteration of loop",
 668                          move_note));
 669             err
 670         } else {
 671             err.span_label(use_span, format!("value {} here after move", verb_participle))
 672                .span_label(move_span, format!("value moved{} here", move_note));
 673             err
 674         };
 675
 676         if need_note {
 677             err.note(&format!("move occurs because `{}` has type `{}`, \
 678                                which does not implement the `Copy` trait",
 679                               self.loan_path_to_string(moved_lp),
 680                               moved_lp.ty));
 681         }
 682
 683         // Note: we used to suggest adding a `ref binding` or calling
 684         // `clone` but those suggestions have been removed because
 685         // they are often not what you actually want to do, and were
 686         // not considered particularly helpful.
 687
 688         err.emit();
 689     }
 690
 691     pub fn report_partial_reinitialization_of_uninitialized_structure(
 692             &self,
 693             span: Span,
 694             lp: &LoanPath<'tcx>) {
 695         span_err!(
 696             self.tcx.sess, span, E0383,
 697             "partial reinitialization of uninitialized structure `{}`",
 698             self.loan_path_to_string(lp));
 699     }
 700
 701     pub fn report_reassigned_immutable_variable(&self,
 702                                                 span: Span,
 703                                                 lp: &LoanPath<'tcx>,
 704                                                 assign:
 705                                                 &move_data::Assignment) {
 706         let mut err = self.cannot_reassign_immutable(span,
 707                                                      &self.loan_path_to_string(lp),
 708                                                      Origin::Ast);
 709         err.span_label(span, "re-assignment of immutable variable");
 710         if span != assign.span {
 711             err.span_label(assign.span, format!("first assignment to `{}`",
 712                                               self.loan_path_to_string(lp)));
 713         }
 714         err.emit();
 715     }
 716
 717     pub fn span_err(&self, s: Span, m: &str) {
 718         self.tcx.sess.span_err(s, m);
 719     }
 720
 721     pub fn struct_span_err<S: Into<MultiSpan>>(&self, s: S, m: &str)
 722                                               -> DiagnosticBuilder<'a> {
 723         self.tcx.sess.struct_span_err(s, m)
 724     }
 725
 726     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 727                                                          s: S,
 728                                                          msg: &str,
 729                                                          code: &str)
 730                                                          -> DiagnosticBuilder<'a> {
 731         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 732     }
 733
 734     pub fn span_err_with_code<S: Into<MultiSpan>>(&self, s: S, msg: &str, code: &str) {
 735         self.tcx.sess.span_err_with_code(s, msg, code);
 736     }
 737
 738     fn bckerr_to_diag(&self, err: &BckError<'tcx>) -> DiagnosticBuilder<'a> {
 739         let span = err.span.clone();
 740
 741         match err.code {
 742             err_mutbl => {
 743                 let descr = match err.cmt.note {
 744                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 745                         self.cmt_to_string(&err.cmt)
 746                     }
 747                     _ => match opt_loan_path(&err.cmt) {
 748                         None => {
 749                             format!("{} {}",
 750                                     err.cmt.mutbl.to_user_str(),
 751                                     self.cmt_to_string(&err.cmt))
 752
 753                         }
 754                         Some(lp) => {
 755                             format!("{} {} `{}`",
 756                                     err.cmt.mutbl.to_user_str(),
 757                                     self.cmt_to_string(&err.cmt),
 758                                     self.loan_path_to_string(&lp))
 759                         }
 760                     }
 761                 };
 762
 763                 match err.cause {
 764                     MutabilityViolation => {
 765                         struct_span_err!(self.tcx.sess, span, E0594, "cannot assign to {}", descr)
 766                     }
 767                     BorrowViolation(euv::ClosureCapture(_)) => {
 768                         struct_span_err!(self.tcx.sess, span, E0595,
 769                                          "closure cannot assign to {}", descr)
 770                     }
 771                     BorrowViolation(euv::OverloadedOperator) |
 772                     BorrowViolation(euv::AddrOf) |
 773                     BorrowViolation(euv::RefBinding) |
 774                     BorrowViolation(euv::AutoRef) |
 775                     BorrowViolation(euv::AutoUnsafe) |
 776                     BorrowViolation(euv::ForLoop) |
 777                     BorrowViolation(euv::MatchDiscriminant) => {
 778                         struct_span_err!(self.tcx.sess, span, E0596,
 779                                          "cannot borrow {} as mutable", descr)
 780                     }
 781                     BorrowViolation(euv::ClosureInvocation) => {
 782                         span_bug!(err.span,
 783                             "err_mutbl with a closure invocation");
 784                     }
 785                 }
 786             }
 787             err_out_of_scope(..) => {
 788                 let msg = match opt_loan_path(&err.cmt) {
 789                     None => "borrowed value".to_string(),
 790                     Some(lp) => {
 791                         format!("`{}`", self.loan_path_to_string(&lp))
 792                     }
 793                 };
 794                 struct_span_err!(self.tcx.sess, span, E0597, "{} does not live long enough", msg)
 795             }
 796             err_borrowed_pointer_too_short(..) => {
 797                 let descr = self.cmt_to_path_or_string(&err.cmt);
 798                 struct_span_err!(self.tcx.sess, span, E0598,
 799                                  "lifetime of {} is too short to guarantee \
 800                                   its contents can be safely reborrowed",
 801                                  descr)
 802             }
 803         }
 804     }
 805
 806     pub fn report_aliasability_violation(&self,
 807                                          span: Span,
 808                                          kind: AliasableViolationKind,
 809                                          cause: mc::AliasableReason,
 810                                          cmt: mc::cmt<'tcx>) {
 811         let mut is_closure = false;
 812         let prefix = match kind {
 813             MutabilityViolation => {
 814                 "cannot assign to data"
 815             }
 816             BorrowViolation(euv::ClosureCapture(_)) |
 817             BorrowViolation(euv::OverloadedOperator) |
 818             BorrowViolation(euv::AddrOf) |
 819             BorrowViolation(euv::AutoRef) |
 820             BorrowViolation(euv::AutoUnsafe) |
 821             BorrowViolation(euv::RefBinding) |
 822             BorrowViolation(euv::MatchDiscriminant) => {
 823                 "cannot borrow data mutably"
 824             }
 825
 826             BorrowViolation(euv::ClosureInvocation) => {
 827                 is_closure = true;
 828                 "closure invocation"
 829             }
 830
 831             BorrowViolation(euv::ForLoop) => {
 832                 "`for` loop"
 833             }
 834         };
 835
 836         match cause {
 837             mc::AliasableStatic |
 838             mc::AliasableStaticMut => {
 839                 // This path cannot occur. It happens when we have an
 840                 // `&mut` or assignment to a static. But in the case
 841                 // of `static X`, we get a mutability violation first,
 842                 // and never get here. In the case of `static mut X`,
 843                 // that is unsafe and hence the aliasability error is
 844                 // ignored.
 845                 span_bug!(span, "aliasability violation for static `{}`", prefix)
 846             }
 847             mc::AliasableBorrowed => {}
 848         };
 849         let blame = cmt.immutability_blame();
 850         let mut err = match blame {
 851             Some(ImmutabilityBlame::ClosureEnv(id)) => {
 852                 let mut err = struct_span_err!(
 853                     self.tcx.sess, span, E0387,
 854                     "{} in a captured outer variable in an `Fn` closure", prefix);
 855
 856                 // FIXME: the distinction between these 2 messages looks wrong.
 857                 let help = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
 858                     // The aliasability violation with closure captures can
 859                     // happen for nested closures, so we know the enclosing
 860                     // closure incorrectly accepts an `Fn` while it needs to
 861                     // be `FnMut`.
 862                     "consider changing this to accept closures that implement `FnMut`"
 863
 864                 } else {
 865                     "consider changing this closure to take self by mutable reference"
 866                 };
 867                 let node_id = self.tcx.hir.def_index_to_node_id(id);
 868                 err.span_help(self.tcx.hir.span(node_id), help);
 869                 err
 870             }
 871             _ =>  {
 872                 let mut err = struct_span_err!(
 873                     self.tcx.sess, span, E0389,
 874                     "{} in a `&` reference", prefix);
 875                 err.span_label(span, "assignment into an immutable reference");
 876                 err
 877             }
 878         };
 879         self.note_immutability_blame(&mut err, blame);
 880
 881         if is_closure {
 882             err.help("closures behind references must be called via `&mut`");
 883         }
 884         err.emit();
 885     }
 886
 887     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
 888     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
 889         // Check wether the argument is an immutable reference
 890         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
 891         if let hir::TyRptr(lifetime, hir::MutTy {
 892             mutbl: hir::Mutability::MutImmutable,
 893             ref ty
 894         }) = pty.node {
 895             // Account for existing lifetimes when generating the message
 896             let pointee_snippet = match self.tcx.sess.codemap().span_to_snippet(ty.span) {
 897                 Ok(snippet) => snippet,
 898                 _ => return None
 899             };
 900
 901             let lifetime_snippet = if !lifetime.is_elided() {
 902                 format!("{} ", match self.tcx.sess.codemap().span_to_snippet(lifetime.span) {
 903                     Ok(lifetime_snippet) => lifetime_snippet,
 904                     _ => return None
 905                 })
 906             } else {
 907                 String::new()
 908             };
 909             Some(format!("use `&{}mut {}` here to make mutable",
 910                          lifetime_snippet,
 911                          if is_implicit_self { "self" } else { &*pointee_snippet }))
 912         } else {
 913             None
 914         }
 915     }
 916
 917     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
 918         let pat = match self.tcx.hir.get(node_id) {
 919             hir_map::Node::NodeLocal(pat) => pat,
 920             node => bug!("bad node for local: {:?}", node)
 921         };
 922
 923         match pat.node {
 924             hir::PatKind::Binding(..) => {
 925                 *self.tables
 926                      .pat_binding_modes()
 927                      .get(pat.hir_id)
 928                      .expect("missing binding mode")
 929             }
 930             _ => bug!("local is not a binding: {:?}", pat)
 931         }
 932     }
 933
 934     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
 935         let parent = self.tcx.hir.get_parent_node(node_id);
 936         let parent_node = self.tcx.hir.get(parent);
 937
 938         // The parent node is like a fn
 939         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
 940             // `nid`'s parent's `Body`
 941             let fn_body = self.tcx.hir.body(fn_like.body());
 942             // Get the position of `node_id` in the arguments list
 943             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
 944             if let Some(i) = arg_pos {
 945                 // The argument's `Ty`
 946                 (Some(&fn_like.decl().inputs[i]),
 947                  i == 0 && fn_like.decl().has_implicit_self)
 948             } else {
 949                 (None, false)
 950             }
 951         } else {
 952             (None, false)
 953         }
 954     }
 955
 956     fn note_immutability_blame(&self,
 957                                db: &mut DiagnosticBuilder,
 958                                blame: Option<ImmutabilityBlame>) {
 959         match blame {
 960             None => {}
 961             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
 962             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
 963                 let let_span = self.tcx.hir.span(node_id);
 964                 if let ty::BindByValue(..) = self.local_binding_mode(node_id) {
 965                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(let_span) {
 966                         let (_, is_implicit_self) = self.local_ty(node_id);
 967                         if is_implicit_self && snippet != "self" {
 968                             // avoid suggesting `mut &self`.
 969                             return
 970                         }
 971                         db.span_label(
 972                             let_span,
 973                             format!("consider changing this to `mut {}`", snippet)
 974                         );
 975                     }
 976                 }
 977             }
 978             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
 979                 let let_span = self.tcx.hir.span(node_id);
 980                 match self.local_binding_mode(node_id) {
 981                     ty::BindByReference(..) => {
 982                         let snippet = self.tcx.sess.codemap().span_to_snippet(let_span);
 983                         if let Ok(snippet) = snippet {
 984                             db.span_label(
 985                                 let_span,
 986                                 format!("consider changing this to `{}`",
 987                                          snippet.replace("ref ", "ref mut "))
 988                             );
 989                         }
 990                     }
 991                     ty::BindByValue(..) => {
 992                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
 993                             if let Some(msg) =
 994                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
 995                                 db.span_label(local_ty.span, msg);
 996                             }
 997                         }
 998                     }
 999                 }
1000             }
1001             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1002                 let node_id = match self.tcx.hir.as_local_node_id(field.did) {
1003                     Some(node_id) => node_id,
1004                     None => return
1005                 };
1006
1007                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(node_id) {
1008                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1009                         db.span_label(field.ty.span, msg);
1010                     }
1011                 }
1012             }
1013         }
1014     }
1015
1016     fn report_out_of_scope_escaping_closure_capture(&self,
1017                                                     err: &BckError<'tcx>,
1018                                                     capture_span: Span)
1019     {
1020         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1021
1022         let suggestion =
1023             match self.tcx.sess.codemap().span_to_snippet(err.span) {
1024                 Ok(string) => format!("move {}", string),
1025                 Err(_) => format!("move |<args>| <body>")
1026             };
1027
1028         struct_span_err!(self.tcx.sess, err.span, E0373,
1029                          "closure may outlive the current function, \
1030                           but it borrows {}, \
1031                           which is owned by the current function",
1032                          cmt_path_or_string)
1033             .span_label(capture_span,
1034                        format!("{} is borrowed here",
1035                                 cmt_path_or_string))
1036             .span_label(err.span,
1037                        format!("may outlive borrowed value {}",
1038                                 cmt_path_or_string))
1039             .span_suggestion(err.span,
1040                              &format!("to force the closure to take ownership of {} \
1041                                        (and any other referenced variables), \
1042                                        use the `move` keyword",
1043                                        cmt_path_or_string),
1044                              suggestion)
1045             .emit();
1046     }
1047
1048     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1049         match *region {
1050             ty::ReScope(scope) => {
1051                 match scope.span(&self.tcx.hir) {
1052                     Some(s) => {
1053                         Some(s.end_point())
1054                     }
1055                     None => {
1056                         None
1057                     }
1058                 }
1059             }
1060             _ => None
1061         }
1062     }
1063
1064     fn note_and_explain_bckerr(&self, db: &mut DiagnosticBuilder, err: BckError<'tcx>) {
1065         let error_span = err.span.clone();
1066         match err.code {
1067             err_mutbl => {
1068                 self.note_and_explain_mutbl_error(db, &err, &error_span);
1069                 self.note_immutability_blame(db, err.cmt.immutability_blame());
1070             }
1071             err_out_of_scope(super_scope, sub_scope, cause) => {
1072                 let (value_kind, value_msg) = match err.cmt.cat {
1073                     mc::Categorization::Rvalue(..) =>
1074                         ("temporary value", "temporary value created here"),
1075                     _ =>
1076                         ("borrowed value", "borrow occurs here")
1077                 };
1078
1079                 let is_closure = match cause {
1080                     euv::ClosureCapture(s) => {
1081                         // The primary span starts out as the closure creation point.
1082                         // Change the primary span here to highlight the use of the variable
1083                         // in the closure, because it seems more natural. Highlight
1084                         // closure creation point as a secondary span.
1085                         match db.span.primary_span() {
1086                             Some(primary) => {
1087                                 db.span = MultiSpan::from_span(s);
1088                                 db.span_label(primary, "capture occurs here");
1089                                 db.span_label(s, "does not live long enough");
1090                                 true
1091                             }
1092                             None => false
1093                         }
1094                     }
1095                     _ => {
1096                         db.span_label(error_span, "does not live long enough");
1097                         false
1098                     }
1099                 };
1100
1101                 let sub_span = self.region_end_span(sub_scope);
1102                 let super_span = self.region_end_span(super_scope);
1103
1104                 match (sub_span, super_span) {
1105                     (Some(s1), Some(s2)) if s1 == s2 => {
1106                         if !is_closure {
1107                             db.span = MultiSpan::from_span(s1);
1108                             db.span_label(error_span, value_msg);
1109                             let msg = match opt_loan_path(&err.cmt) {
1110                                 None => value_kind.to_string(),
1111                                 Some(lp) => {
1112                                     format!("`{}`", self.loan_path_to_string(&lp))
1113                                 }
1114                             };
1115                             db.span_label(s1,
1116                                           format!("{} dropped here while still borrowed", msg));
1117                         } else {
1118                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
1119                         }
1120                         db.note("values in a scope are dropped in the opposite order \
1121                                 they are created");
1122                     }
1123                     (Some(s1), Some(s2)) if !is_closure => {
1124                         db.span = MultiSpan::from_span(s2);
1125                         db.span_label(error_span, value_msg);
1126                         let msg = match opt_loan_path(&err.cmt) {
1127                             None => value_kind.to_string(),
1128                             Some(lp) => {
1129                                 format!("`{}`", self.loan_path_to_string(&lp))
1130                             }
1131                         };
1132                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
1133                         db.span_label(s1, format!("{} needs to live until here", value_kind));
1134                     }
1135                     _ => {
1136                         match sub_span {
1137                             Some(s) => {
1138                                 db.span_label(s, format!("{} needs to live until here",
1139                                                           value_kind));
1140                             }
1141                             None => {
1142                                 self.tcx.note_and_explain_region(
1143                                     db,
1144                                     "borrowed value must be valid for ",
1145                                     sub_scope,
1146                                     "...");
1147                             }
1148                         }
1149                         match super_span {
1150                             Some(s) => {
1151                                 db.span_label(s, format!("{} only lives until here", value_kind));
1152                             }
1153                             None => {
1154                                 self.tcx.note_and_explain_region(
1155                                     db,
1156                                     "...but borrowed value is only valid for ",
1157                                     super_scope,
1158                                     "");
1159                             }
1160                         }
1161                     }
1162                 }
1163
1164                 if let Some(_) = statement_scope_span(self.tcx, super_scope) {
1165                     db.note("consider using a `let` binding to increase its lifetime");
1166                 }
1167             }
1168
1169             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1170                 let descr = match opt_loan_path(&err.cmt) {
1171                     Some(lp) => {
1172                         format!("`{}`", self.loan_path_to_string(&lp))
1173                     }
1174                     None => self.cmt_to_string(&err.cmt),
1175                 };
1176                 self.tcx.note_and_explain_region(
1177                     db,
1178                     &format!("{} would have to be valid for ",
1179                             descr),
1180                     loan_scope,
1181                     "...");
1182                 self.tcx.note_and_explain_region(
1183                     db,
1184                     &format!("...but {} is only valid for ", descr),
1185                     ptr_scope,
1186                     "");
1187             }
1188         }
1189     }
1190
1191     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1192                                     error_span: &Span) {
1193         match err.cmt.note {
1194             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1195                 // If this is an `Fn` closure, it simply can't mutate upvars.
1196                 // If it's an `FnMut` closure, the original variable was declared immutable.
1197                 // We need to determine which is the case here.
1198                 let kind = match err.cmt.upvar().unwrap().cat {
1199                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1200                     _ => bug!()
1201                 };
1202                 if kind == ty::ClosureKind::Fn {
1203                     let closure_node_id =
1204                         self.tcx.hir.def_index_to_node_id(upvar_id.closure_expr_id);
1205                     db.span_help(self.tcx.hir.span(closure_node_id),
1206                                  "consider changing this closure to take \
1207                                   self by mutable reference");
1208                 }
1209             }
1210             _ => {
1211                 if let Categorization::Deref(..) = err.cmt.cat {
1212                     db.span_label(*error_span, "cannot borrow as mutable");
1213                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1214                     let span = self.tcx.hir.span(local_id);
1215                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1216                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1217                             db.span_label(*error_span, "cannot reborrow mutably");
1218                             db.span_label(*error_span, "try removing `&mut` here");
1219                         } else {
1220                             db.span_label(*error_span, "cannot borrow mutably");
1221                         }
1222                     } else {
1223                         db.span_label(*error_span, "cannot borrow mutably");
1224                     }
1225                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1226                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1227                         db.span_label(*error_span,
1228                                       "cannot mutably borrow immutable field");
1229                     }
1230                 }
1231             }
1232         }
1233     }
1234     pub fn append_loan_path_to_string(&self,
1235                                       loan_path: &LoanPath<'tcx>,
1236                                       out: &mut String) {
1237         match loan_path.kind {
1238             LpUpvar(ty::UpvarId { var_id: id, closure_expr_id: _ }) => {
1239                 out.push_str(&self.tcx.local_var_name_str_def_index(id));
1240             }
1241             LpVar(id) => {
1242                 out.push_str(&self.tcx.local_var_name_str(id));
1243             }
1244
1245             LpDowncast(ref lp_base, variant_def_id) => {
1246                 out.push('(');
1247                 self.append_loan_path_to_string(&lp_base, out);
1248                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1249                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1250                 out.push(')');
1251             }
1252
1253             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1254                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1255                 match fname {
1256                     mc::NamedField(fname) => {
1257                         out.push('.');
1258                         out.push_str(&fname.as_str());
1259                     }
1260                     mc::PositionalField(idx) => {
1261                         out.push('.');
1262                         out.push_str(&idx.to_string());
1263                     }
1264                 }
1265             }
1266
1267             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1268                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1269                 out.push_str("[..]");
1270             }
1271
1272             LpExtend(ref lp_base, _, LpDeref(_)) => {
1273                 out.push('*');
1274                 self.append_loan_path_to_string(&lp_base, out);
1275             }
1276         }
1277     }
1278
1279     pub fn append_autoderefd_loan_path_to_string(&self,
1280                                                  loan_path: &LoanPath<'tcx>,
1281                                                  out: &mut String) {
1282         match loan_path.kind {
1283             LpExtend(ref lp_base, _, LpDeref(_)) => {
1284                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1285                 // rules would normally allow users to omit the `*x`.
1286                 // So just serialize such paths to `x.f` or x[3]` respectively.
1287                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1288             }
1289
1290             LpDowncast(ref lp_base, variant_def_id) => {
1291                 out.push('(');
1292                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1293                 out.push(':');
1294                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1295                 out.push(')');
1296             }
1297
1298             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1299                 self.append_loan_path_to_string(loan_path, out)
1300             }
1301         }
1302     }
1303
1304     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1305         let mut result = String::new();
1306         self.append_loan_path_to_string(loan_path, &mut result);
1307         result
1308     }
1309
1310     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1311         cmt.descriptive_string(self.tcx)
1312     }
1313
1314     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1315         match opt_loan_path(cmt) {
1316             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1317             None => self.cmt_to_string(cmt),
1318         }
1319     }
1320 }
1321
1322 fn statement_scope_span(tcx: TyCtxt, region: ty::Region) -> Option<Span> {
1323     match *region {
1324         ty::ReScope(scope) => {
1325             match tcx.hir.find(scope.node_id()) {
1326                 Some(hir_map::NodeStmt(stmt)) => Some(stmt.span),
1327                 _ => None
1328             }
1329         }
1330         _ => None
1331     }
1332 }
1333
1334 impl BitwiseOperator for LoanDataFlowOperator {
1335     #[inline]
1336     fn join(&self, succ: usize, pred: usize) -> usize {
1337         succ | pred // loans from both preds are in scope
1338     }
1339 }
1340
1341 impl DataFlowOperator for LoanDataFlowOperator {
1342     #[inline]
1343     fn initial_value(&self) -> bool {
1344         false // no loans in scope by default
1345     }
1346 }
1347
1348 impl<'tcx> fmt::Debug for InteriorKind {
1349     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1350         match *self {
1351             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1352             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1353             InteriorElement => write!(f, "[]"),
1354         }
1355     }
1356 }
1357
1358 impl<'tcx> fmt::Debug for Loan<'tcx> {
1359     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1360         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1361                self.index,
1362                self.loan_path,
1363                self.kind,
1364                self.gen_scope,
1365                self.kill_scope,
1366                self.restricted_paths)
1367     }
1368 }
1369
1370 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1371     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1372         match self.kind {
1373             LpVar(id) => {
1374                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1375             }
1376
1377             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1378                 let s = ty::tls::with(|tcx| {
1379                     let var_node_id = tcx.hir.def_index_to_node_id(var_id);
1380                     tcx.hir.node_to_string(var_node_id)
1381                 });
1382                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1383             }
1384
1385             LpDowncast(ref lp, variant_def_id) => {
1386                 let variant_str = if variant_def_id.is_local() {
1387                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1388                 } else {
1389                     format!("{:?}", variant_def_id)
1390                 };
1391                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1392             }
1393
1394             LpExtend(ref lp, _, LpDeref(_)) => {
1395                 write!(f, "{:?}.*", lp)
1396             }
1397
1398             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1399                 write!(f, "{:?}.{:?}", lp, interior)
1400             }
1401         }
1402     }
1403 }
1404
1405 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1406     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1407         match self.kind {
1408             LpVar(id) => {
1409                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1410             }
1411
1412             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1413                 let s = ty::tls::with(|tcx| {
1414                     let var_node_id = tcx.hir.def_index_to_node_id(var_id);
1415                     tcx.hir.node_to_string(var_node_id)
1416                 });
1417                 write!(f, "$({} captured by closure)", s)
1418             }
1419
1420             LpDowncast(ref lp, variant_def_id) => {
1421                 let variant_str = if variant_def_id.is_local() {
1422                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1423                 } else {
1424                     format!("{:?}", variant_def_id)
1425                 };
1426                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1427             }
1428
1429             LpExtend(ref lp, _, LpDeref(_)) => {
1430                 write!(f, "{}.*", lp)
1431             }
1432
1433             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1434                 write!(f, "{}.{:?}", lp, interior)
1435             }
1436         }
1437     }
1438 }