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 pub use self::mir::elaborate_drops::ElaborateDrops;
  22
  23 use self::InteriorKind::*;
  24
  25 use rustc::dep_graph::DepNode;
  26 use rustc::hir::map as hir_map;
  27 use rustc::hir::map::blocks::FnLikeNode;
  28 use rustc::cfg;
  29 use rustc::middle::dataflow::DataFlowContext;
  30 use rustc::middle::dataflow::BitwiseOperator;
  31 use rustc::middle::dataflow::DataFlowOperator;
  32 use rustc::middle::dataflow::KillFrom;
  33 use rustc::hir::def_id::DefId;
  34 use rustc::middle::expr_use_visitor as euv;
  35 use rustc::middle::mem_categorization as mc;
  36 use rustc::middle::mem_categorization::Categorization;
  37 use rustc::middle::region;
  38 use rustc::ty::{self, TyCtxt};
  39
  40 use std::fmt;
  41 use std::rc::Rc;
  42 use std::hash::{Hash, Hasher};
  43 use syntax::ast;
  44 use syntax_pos::{MultiSpan, Span};
  45 use errors::DiagnosticBuilder;
  46
  47 use rustc::hir;
  48 use rustc::hir::intravisit::{self, Visitor};
  49
  50 pub mod check_loans;
  51
  52 pub mod gather_loans;
  53
  54 pub mod move_data;
  55
  56 mod mir;
  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     tcx.dep_graph.with_task(DepNode::BorrowCheckKrate, tcx, (), check_crate_task);
  65
  66     fn check_crate_task<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, (): ()) {
  67         tcx.visit_all_bodies_in_krate(|body_owner_def_id, body_id| {
  68             tcx.dep_graph.with_task(DepNode::BorrowCheck(body_owner_def_id),
  69                                     tcx,
  70                                     body_id,
  71                                     borrowck_fn);
  72         });
  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_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, body_id: hir::BodyId) {
  84     debug!("borrowck_fn(body_id={:?})", body_id);
  85
  86     let owner_id = tcx.hir.body_owner(body_id);
  87     let owner_def_id = tcx.hir.local_def_id(owner_id);
  88     let attributes = tcx.get_attrs(owner_def_id);
  89     let tables = tcx.item_tables(owner_def_id);
  90
  91     let mut bccx = &mut BorrowckCtxt {
  92         tcx: tcx,
  93         tables: tables,
  94     };
  95
  96     let body = bccx.tcx.hir.body(body_id);
  97
  98     if bccx.tcx.has_attr(owner_def_id, "rustc_mir_borrowck") {
  99         mir::borrowck_mir(bccx, owner_id, &attributes);
 100     }
 101
 102     let cfg = cfg::CFG::new(bccx.tcx, &body);
 103     let AnalysisData { all_loans,
 104                        loans: loan_dfcx,
 105                        move_data: flowed_moves } =
 106         build_borrowck_dataflow_data(bccx, &cfg, body_id);
 107
 108     move_data::fragments::instrument_move_fragments(&flowed_moves.move_data,
 109                                                     bccx.tcx,
 110                                                     owner_id);
 111     move_data::fragments::build_unfragmented_map(bccx,
 112                                                  &flowed_moves.move_data,
 113                                                  owner_id);
 114
 115     check_loans::check_loans(bccx, &loan_dfcx, &flowed_moves, &all_loans[..], body);
 116 }
 117
 118 fn build_borrowck_dataflow_data<'a, 'tcx>(this: &mut BorrowckCtxt<'a, 'tcx>,
 119                                           cfg: &cfg::CFG,
 120                                           body_id: hir::BodyId)
 121                                           -> AnalysisData<'a, 'tcx>
 122 {
 123     // Check the body of fn items.
 124     let tcx = this.tcx;
 125     let body = tcx.hir.body(body_id);
 126     let id_range = {
 127         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 128         visitor.visit_body(body);
 129         visitor.result()
 130     };
 131     let (all_loans, move_data) =
 132         gather_loans::gather_loans_in_fn(this, body_id);
 133
 134     let mut loan_dfcx =
 135         DataFlowContext::new(this.tcx,
 136                              "borrowck",
 137                              Some(body),
 138                              cfg,
 139                              LoanDataFlowOperator,
 140                              id_range,
 141                              all_loans.len());
 142     for (loan_idx, loan) in all_loans.iter().enumerate() {
 143         loan_dfcx.add_gen(loan.gen_scope.node_id(&tcx.region_maps), loan_idx);
 144         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 145                            loan.kill_scope.node_id(&tcx.region_maps), loan_idx);
 146     }
 147     loan_dfcx.add_kills_from_flow_exits(cfg);
 148     loan_dfcx.propagate(cfg, body);
 149
 150     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 151                                                       this.tcx,
 152                                                       cfg,
 153                                                       id_range,
 154                                                       body);
 155
 156     AnalysisData { all_loans: all_loans,
 157                    loans: loan_dfcx,
 158                    move_data:flowed_moves }
 159 }
 160
 161 /// Accessor for introspective clients inspecting `AnalysisData` and
 162 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 163 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 164     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 165     body_id: hir::BodyId,
 166     cfg: &cfg::CFG)
 167     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 168 {
 169     let owner_id = tcx.hir.body_owner(body_id);
 170     let owner_def_id = tcx.hir.local_def_id(owner_id);
 171     let tables = tcx.item_tables(owner_def_id);
 172
 173     let mut bccx = BorrowckCtxt {
 174         tcx: tcx,
 175         tables: tables,
 176     };
 177
 178     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, cfg, body_id);
 179     (bccx, dataflow_data)
 180 }
 181
 182 // ----------------------------------------------------------------------
 183 // Type definitions
 184
 185 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 186     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 187
 188     // tables for the current thing we are checking; set to
 189     // Some in `borrowck_fn` and cleared later
 190     tables: &'a ty::TypeckTables<'tcx>,
 191 }
 192
 193 ///////////////////////////////////////////////////////////////////////////
 194 // Loans and loan paths
 195
 196 /// Record of a loan that was issued.
 197 pub struct Loan<'tcx> {
 198     index: usize,
 199     loan_path: Rc<LoanPath<'tcx>>,
 200     kind: ty::BorrowKind,
 201     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 202
 203     /// gen_scope indicates where loan is introduced. Typically the
 204     /// loan is introduced at the point of the borrow, but in some
 205     /// cases, notably method arguments, the loan may be introduced
 206     /// only later, once it comes into scope.  See also
 207     /// `GatherLoanCtxt::compute_gen_scope`.
 208     gen_scope: region::CodeExtent,
 209
 210     /// kill_scope indicates when the loan goes out of scope.  This is
 211     /// either when the lifetime expires or when the local variable
 212     /// which roots the loan-path goes out of scope, whichever happens
 213     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 214     kill_scope: region::CodeExtent,
 215     span: Span,
 216     cause: euv::LoanCause,
 217 }
 218
 219 impl<'tcx> Loan<'tcx> {
 220     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 221         self.loan_path.clone()
 222     }
 223 }
 224
 225 #[derive(Eq)]
 226 pub struct LoanPath<'tcx> {
 227     kind: LoanPathKind<'tcx>,
 228     ty: ty::Ty<'tcx>,
 229 }
 230
 231 impl<'tcx> PartialEq for LoanPath<'tcx> {
 232     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 233         self.kind == that.kind
 234     }
 235 }
 236
 237 impl<'tcx> Hash for LoanPath<'tcx> {
 238     fn hash<H: Hasher>(&self, state: &mut H) {
 239         self.kind.hash(state);
 240     }
 241 }
 242
 243 #[derive(PartialEq, Eq, Hash, Debug)]
 244 pub enum LoanPathKind<'tcx> {
 245     LpVar(ast::NodeId),                         // `x` in README.md
 246     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 247     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 248     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 249 }
 250
 251 impl<'tcx> LoanPath<'tcx> {
 252     fn new(kind: LoanPathKind<'tcx>, ty: ty::Ty<'tcx>) -> LoanPath<'tcx> {
 253         LoanPath { kind: kind, ty: ty }
 254     }
 255
 256     fn to_type(&self) -> ty::Ty<'tcx> { self.ty }
 257 }
 258
 259 // FIXME (pnkfelix): See discussion here
 260 // https://github.com/pnkfelix/rust/commit/
 261 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 262 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 263
 264 // A local, "cleaned" version of `mc::InteriorKind` that drops
 265 // information that is not relevant to loan-path analysis. (In
 266 // particular, the distinction between how precisely an array-element
 267 // is tracked is irrelevant here.)
 268 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 269 pub enum InteriorKind {
 270     InteriorField(mc::FieldName),
 271     InteriorElement(mc::ElementKind),
 272 }
 273
 274 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 275 impl ToInteriorKind for mc::InteriorKind {
 276     fn cleaned(self) -> InteriorKind {
 277         match self {
 278             mc::InteriorField(name) => InteriorField(name),
 279             mc::InteriorElement(_, elem_kind) => InteriorElement(elem_kind),
 280         }
 281     }
 282 }
 283
 284 // This can be:
 285 // - a pointer dereference (`*LV` in README.md)
 286 // - a field reference, with an optional definition of the containing
 287 //   enum variant (`LV.f` in README.md)
 288 // `DefId` is present when the field is part of struct that is in
 289 // a variant of an enum. For instance in:
 290 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 291 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 292 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 293 pub enum LoanPathElem<'tcx> {
 294     LpDeref(mc::PointerKind<'tcx>),
 295     LpInterior(Option<DefId>, InteriorKind),
 296 }
 297
 298 pub fn closure_to_block(closure_id: ast::NodeId,
 299                         tcx: TyCtxt) -> ast::NodeId {
 300     match tcx.hir.get(closure_id) {
 301         hir_map::NodeExpr(expr) => match expr.node {
 302             hir::ExprClosure(.., body_id, _) => {
 303                 body_id.node_id
 304             }
 305             _ => {
 306                 bug!("encountered non-closure id: {}", closure_id)
 307             }
 308         },
 309         _ => bug!("encountered non-expr id: {}", closure_id)
 310     }
 311 }
 312
 313 impl<'a, 'tcx> LoanPath<'tcx> {
 314     pub fn kill_scope(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> region::CodeExtent {
 315         match self.kind {
 316             LpVar(local_id) => tcx.region_maps.var_scope(local_id),
 317             LpUpvar(upvar_id) => {
 318                 let block_id = closure_to_block(upvar_id.closure_expr_id, tcx);
 319                 tcx.region_maps.node_extent(block_id)
 320             }
 321             LpDowncast(ref base, _) |
 322             LpExtend(ref base, ..) => base.kill_scope(tcx),
 323         }
 324     }
 325
 326     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 327         match (&self.kind, &other.kind) {
 328             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 329              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 330                 if id == id2 && opt_variant_id == opt_variant_id2 {
 331                     base.has_fork(&base2)
 332                 } else {
 333                     true
 334                 },
 335             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 336             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 337             _ => false,
 338         }
 339     }
 340
 341     fn depth(&self) -> usize {
 342         match self.kind {
 343             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 344             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 345             _ => 0,
 346         }
 347     }
 348
 349     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 350         match (&self.kind, &other.kind) {
 351             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 352              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 353                 if id == id2 && opt_variant_id == opt_variant_id2 {
 354                     base.common(&base2).map(|x| {
 355                         let xd = x.depth();
 356                         if base.depth() == xd && base2.depth() == xd {
 357                             LoanPath {
 358                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 359                                 ty: self.ty,
 360                             }
 361                         } else {
 362                             x
 363                         }
 364                     })
 365                 } else {
 366                     base.common(&base2)
 367                 }
 368             }
 369             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 370             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 371             (&LpVar(id), &LpVar(id2)) => {
 372                 if id == id2 {
 373                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 374                 } else {
 375                     None
 376                 }
 377             }
 378             (&LpUpvar(id), &LpUpvar(id2)) => {
 379                 if id == id2 {
 380                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 381                 } else {
 382                     None
 383                 }
 384             }
 385             _ => None,
 386         }
 387     }
 388 }
 389
 390 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 391     //! Computes the `LoanPath` (if any) for a `cmt`.
 392     //! Note that this logic is somewhat duplicated in
 393     //! the method `compute()` found in `gather_loans::restrictions`,
 394     //! which allows it to share common loan path pieces as it
 395     //! traverses the CMT.
 396
 397     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 398
 399     match cmt.cat {
 400         Categorization::Rvalue(..) |
 401         Categorization::StaticItem => {
 402             None
 403         }
 404
 405         Categorization::Local(id) => {
 406             Some(new_lp(LpVar(id)))
 407         }
 408
 409         Categorization::Upvar(mc::Upvar { id, .. }) => {
 410             Some(new_lp(LpUpvar(id)))
 411         }
 412
 413         Categorization::Deref(ref cmt_base, _, pk) => {
 414             opt_loan_path(cmt_base).map(|lp| {
 415                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 416             })
 417         }
 418
 419         Categorization::Interior(ref cmt_base, ik) => {
 420             opt_loan_path(cmt_base).map(|lp| {
 421                 let opt_variant_id = match cmt_base.cat {
 422                     Categorization::Downcast(_, did) =>  Some(did),
 423                     _ => None
 424                 };
 425                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 426             })
 427         }
 428
 429         Categorization::Downcast(ref cmt_base, variant_def_id) =>
 430             opt_loan_path(cmt_base)
 431             .map(|lp| {
 432                 new_lp(LpDowncast(lp, variant_def_id))
 433             }),
 434
 435     }
 436 }
 437
 438 ///////////////////////////////////////////////////////////////////////////
 439 // Errors
 440
 441 // Errors that can occur
 442 #[derive(Debug, PartialEq)]
 443 pub enum bckerr_code<'tcx> {
 444     err_mutbl,
 445     /// superscope, subscope, loan cause
 446     err_out_of_scope(&'tcx ty::Region, &'tcx ty::Region, euv::LoanCause),
 447     err_borrowed_pointer_too_short(&'tcx ty::Region, &'tcx ty::Region), // loan, ptr
 448 }
 449
 450 // Combination of an error code and the categorization of the expression
 451 // that caused it
 452 #[derive(Debug, PartialEq)]
 453 pub struct BckError<'tcx> {
 454     span: Span,
 455     cause: AliasableViolationKind,
 456     cmt: mc::cmt<'tcx>,
 457     code: bckerr_code<'tcx>
 458 }
 459
 460 #[derive(Copy, Clone, Debug, PartialEq)]
 461 pub enum AliasableViolationKind {
 462     MutabilityViolation,
 463     BorrowViolation(euv::LoanCause)
 464 }
 465
 466 #[derive(Copy, Clone, Debug)]
 467 pub enum MovedValueUseKind {
 468     MovedInUse,
 469     MovedInCapture,
 470 }
 471
 472 ///////////////////////////////////////////////////////////////////////////
 473 // Misc
 474
 475 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 476     pub fn is_subregion_of(&self,
 477                            r_sub: &'tcx ty::Region,
 478                            r_sup: &'tcx ty::Region)
 479                            -> bool
 480     {
 481         self.tables.free_region_map.is_subregion_of(self.tcx, r_sub, r_sup)
 482     }
 483
 484     pub fn report(&self, err: BckError<'tcx>) {
 485         // Catch and handle some particular cases.
 486         match (&err.code, &err.cause) {
 487             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 488              &BorrowViolation(euv::ClosureCapture(span))) |
 489             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 490              &BorrowViolation(euv::ClosureCapture(span))) => {
 491                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 492             }
 493             _ => { }
 494         }
 495
 496         let mut db = self.bckerr_to_diag(&err);
 497         self.note_and_explain_bckerr(&mut db, err);
 498         db.emit();
 499     }
 500
 501     pub fn report_use_of_moved_value(&self,
 502                                      use_span: Span,
 503                                      use_kind: MovedValueUseKind,
 504                                      lp: &LoanPath<'tcx>,
 505                                      the_move: &move_data::Move,
 506                                      moved_lp: &LoanPath<'tcx>,
 507                                      _param_env: &ty::ParameterEnvironment<'tcx>) {
 508         let (verb, verb_participle) = match use_kind {
 509             MovedInUse => ("use", "used"),
 510             MovedInCapture => ("capture", "captured"),
 511         };
 512
 513         let (_ol, _moved_lp_msg, mut err) = match the_move.kind {
 514             move_data::Declared => {
 515                 // If this is an uninitialized variable, just emit a simple warning
 516                 // and return.
 517                 struct_span_err!(
 518                     self.tcx.sess, use_span, E0381,
 519                     "{} of possibly uninitialized variable: `{}`",
 520                     verb,
 521                     self.loan_path_to_string(lp))
 522                 .span_label(use_span, &format!("use of possibly uninitialized `{}`",
 523                     self.loan_path_to_string(lp)))
 524                 .emit();
 525                 return;
 526             }
 527             _ => {
 528                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 529                 // normally generate a rather confusing message:
 530                 //
 531                 //     error: use of moved value: `x.b`
 532                 //     note: `x.a` moved here...
 533                 //
 534                 // What we want to do instead is get the 'common ancestor' of the two moves and
 535                 // use that for most of the message instead, giving is something like this:
 536                 //
 537                 //     error: use of moved value: `x`
 538                 //     note: `x` moved here (through moving `x.a`)...
 539
 540                 let common = moved_lp.common(lp);
 541                 let has_common = common.is_some();
 542                 let has_fork = moved_lp.has_fork(lp);
 543                 let (nl, ol, moved_lp_msg) =
 544                     if has_fork && has_common {
 545                         let nl = self.loan_path_to_string(&common.unwrap());
 546                         let ol = nl.clone();
 547                         let moved_lp_msg = format!(" (through moving `{}`)",
 548                                                    self.loan_path_to_string(moved_lp));
 549                         (nl, ol, moved_lp_msg)
 550                     } else {
 551                         (self.loan_path_to_string(lp),
 552                          self.loan_path_to_string(moved_lp),
 553                          String::new())
 554                     };
 555
 556                 let partial = moved_lp.depth() > lp.depth();
 557                 let msg = if !has_fork && partial { "partially " }
 558                           else if has_fork && !has_common { "collaterally "}
 559                           else { "" };
 560                 let err = struct_span_err!(
 561                     self.tcx.sess, use_span, E0382,
 562                     "{} of {}moved value: `{}`",
 563                     verb, msg, nl);
 564                 (ol, moved_lp_msg, err)}
 565         };
 566
 567         // Get type of value and span where it was previously
 568         // moved.
 569         let (move_span, move_note) = match the_move.kind {
 570             move_data::Declared => {
 571                 unreachable!();
 572             }
 573
 574             move_data::MoveExpr |
 575             move_data::MovePat =>
 576                 (self.tcx.hir.span(the_move.id), ""),
 577
 578             move_data::Captured =>
 579                 (match self.tcx.hir.expect_expr(the_move.id).node {
 580                     hir::ExprClosure(.., fn_decl_span) => fn_decl_span,
 581                     ref r => bug!("Captured({}) maps to non-closure: {:?}",
 582                                   the_move.id, r),
 583                 }, " (into closure)"),
 584         };
 585
 586         // Annotate the use and the move in the span. Watch out for
 587         // the case where the use and the move are the same. This
 588         // means the use is in a loop.
 589         err = if use_span == move_span {
 590             err.span_label(
 591                 use_span,
 592                 &format!("value moved{} here in previous iteration of loop",
 593                          move_note));
 594             err
 595         } else {
 596             err.span_label(use_span, &format!("value {} here after move", verb_participle))
 597                .span_label(move_span, &format!("value moved{} here", move_note));
 598             err
 599         };
 600
 601         err.note(&format!("move occurs because `{}` has type `{}`, \
 602                            which does not implement the `Copy` trait",
 603                           self.loan_path_to_string(moved_lp),
 604                           moved_lp.ty));
 605
 606         // Note: we used to suggest adding a `ref binding` or calling
 607         // `clone` but those suggestions have been removed because
 608         // they are often not what you actually want to do, and were
 609         // not considered particularly helpful.
 610
 611         err.emit();
 612     }
 613
 614     pub fn report_partial_reinitialization_of_uninitialized_structure(
 615             &self,
 616             span: Span,
 617             lp: &LoanPath<'tcx>) {
 618         span_err!(
 619             self.tcx.sess, span, E0383,
 620             "partial reinitialization of uninitialized structure `{}`",
 621             self.loan_path_to_string(lp));
 622     }
 623
 624     pub fn report_reassigned_immutable_variable(&self,
 625                                                 span: Span,
 626                                                 lp: &LoanPath<'tcx>,
 627                                                 assign:
 628                                                 &move_data::Assignment) {
 629         let mut err = struct_span_err!(
 630             self.tcx.sess, span, E0384,
 631             "re-assignment of immutable variable `{}`",
 632             self.loan_path_to_string(lp));
 633         err.span_label(span, &format!("re-assignment of immutable variable"));
 634         if span != assign.span {
 635             err.span_label(assign.span, &format!("first assignment to `{}`",
 636                                               self.loan_path_to_string(lp)));
 637         }
 638         err.emit();
 639     }
 640
 641     pub fn span_err(&self, s: Span, m: &str) {
 642         self.tcx.sess.span_err(s, m);
 643     }
 644
 645     pub fn struct_span_err<S: Into<MultiSpan>>(&self, s: S, m: &str)
 646                                               -> DiagnosticBuilder<'a> {
 647         self.tcx.sess.struct_span_err(s, m)
 648     }
 649
 650     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 651                                                          s: S,
 652                                                          msg: &str,
 653                                                          code: &str)
 654                                                          -> DiagnosticBuilder<'a> {
 655         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 656     }
 657
 658     pub fn span_err_with_code<S: Into<MultiSpan>>(&self, s: S, msg: &str, code: &str) {
 659         self.tcx.sess.span_err_with_code(s, msg, code);
 660     }
 661
 662     pub fn bckerr_to_diag(&self, err: &BckError<'tcx>) -> DiagnosticBuilder<'a> {
 663         let span = err.span.clone();
 664         let mut immutable_field = None;
 665
 666         let msg = &match err.code {
 667             err_mutbl => {
 668                 let descr = match err.cmt.note {
 669                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 670                         self.cmt_to_string(&err.cmt)
 671                     }
 672                     _ => match opt_loan_path(&err.cmt) {
 673                         None => {
 674                             format!("{} {}",
 675                                     err.cmt.mutbl.to_user_str(),
 676                                     self.cmt_to_string(&err.cmt))
 677
 678                         }
 679                         Some(lp) => {
 680                             format!("{} {} `{}`",
 681                                     err.cmt.mutbl.to_user_str(),
 682                                     self.cmt_to_string(&err.cmt),
 683                                     self.loan_path_to_string(&lp))
 684                         }
 685                     }
 686                 };
 687
 688                 match err.cause {
 689                     MutabilityViolation => {
 690                         format!("cannot assign to {}", descr)
 691                     }
 692                     BorrowViolation(euv::ClosureCapture(_)) => {
 693                         format!("closure cannot assign to {}", descr)
 694                     }
 695                     BorrowViolation(euv::OverloadedOperator) |
 696                     BorrowViolation(euv::AddrOf) |
 697                     BorrowViolation(euv::RefBinding) |
 698                     BorrowViolation(euv::AutoRef) |
 699                     BorrowViolation(euv::AutoUnsafe) |
 700                     BorrowViolation(euv::ForLoop) |
 701                     BorrowViolation(euv::MatchDiscriminant) => {
 702                         // Check for this field's definition to see if it is an immutable reference
 703                         // and suggest making it mutable if that is the case.
 704                         immutable_field = err.cmt.get_field_name()
 705                             .and_then(|name| err.cmt.get_field(name))
 706                             .and_then(|did| self.tcx.hir.as_local_node_id(did))
 707                             .and_then(|nid| {
 708                                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(nid) {
 709                                     return self.suggest_mut_for_immutable(&field.ty)
 710                                         .map(|msg| (self.tcx.hir.span(nid), msg));
 711                                 }
 712                                 None
 713                             });
 714
 715                         format!("cannot borrow {} as mutable", descr)
 716                     }
 717                     BorrowViolation(euv::ClosureInvocation) => {
 718                         span_bug!(err.span,
 719                             "err_mutbl with a closure invocation");
 720                     }
 721                 }
 722             }
 723             err_out_of_scope(..) => {
 724                 let msg = match opt_loan_path(&err.cmt) {
 725                     None => "borrowed value".to_string(),
 726                     Some(lp) => {
 727                         format!("`{}`", self.loan_path_to_string(&lp))
 728                     }
 729                 };
 730                 format!("{} does not live long enough", msg)
 731             }
 732             err_borrowed_pointer_too_short(..) => {
 733                 let descr = self.cmt_to_path_or_string(&err.cmt);
 734                 format!("lifetime of {} is too short to guarantee \
 735                          its contents can be safely reborrowed",
 736                         descr)
 737             }
 738         };
 739
 740         let mut db = self.struct_span_err(span, msg);
 741         if let Some((span, msg)) = immutable_field {
 742             db.span_label(span, &msg);
 743         }
 744         db
 745     }
 746
 747     pub fn report_aliasability_violation(&self,
 748                                          span: Span,
 749                                          kind: AliasableViolationKind,
 750                                          cause: mc::AliasableReason,
 751                                          cmt: mc::cmt<'tcx>) {
 752         let mut is_closure = false;
 753         let prefix = match kind {
 754             MutabilityViolation => {
 755                 "cannot assign to data"
 756             }
 757             BorrowViolation(euv::ClosureCapture(_)) |
 758             BorrowViolation(euv::OverloadedOperator) |
 759             BorrowViolation(euv::AddrOf) |
 760             BorrowViolation(euv::AutoRef) |
 761             BorrowViolation(euv::AutoUnsafe) |
 762             BorrowViolation(euv::RefBinding) |
 763             BorrowViolation(euv::MatchDiscriminant) => {
 764                 "cannot borrow data mutably"
 765             }
 766
 767             BorrowViolation(euv::ClosureInvocation) => {
 768                 is_closure = true;
 769                 "closure invocation"
 770             }
 771
 772             BorrowViolation(euv::ForLoop) => {
 773                 "`for` loop"
 774             }
 775         };
 776
 777         let mut err = match cause {
 778             mc::AliasableOther => {
 779                 struct_span_err!(
 780                     self.tcx.sess, span, E0385,
 781                     "{} in an aliasable location", prefix)
 782             }
 783             mc::AliasableReason::UnaliasableImmutable => {
 784                 struct_span_err!(
 785                     self.tcx.sess, span, E0386,
 786                     "{} in an immutable container", prefix)
 787             }
 788             mc::AliasableClosure(id) => {
 789                 let mut err = struct_span_err!(
 790                     self.tcx.sess, span, E0387,
 791                     "{} in a captured outer variable in an `Fn` closure", prefix);
 792                 if let BorrowViolation(euv::ClosureCapture(_)) = kind {
 793                     // The aliasability violation with closure captures can
 794                     // happen for nested closures, so we know the enclosing
 795                     // closure incorrectly accepts an `Fn` while it needs to
 796                     // be `FnMut`.
 797                     span_help!(&mut err, self.tcx.hir.span(id),
 798                            "consider changing this to accept closures that implement `FnMut`");
 799                 } else {
 800                     span_help!(&mut err, self.tcx.hir.span(id),
 801                            "consider changing this closure to take self by mutable reference");
 802                 }
 803                 err
 804             }
 805             mc::AliasableStatic |
 806             mc::AliasableStaticMut => {
 807                 // This path cannot occur. It happens when we have an
 808                 // `&mut` or assignment to a static. But in the case
 809                 // of `static X`, we get a mutability violation first,
 810                 // and never get here. In the case of `static mut X`,
 811                 // that is unsafe and hence the aliasability error is
 812                 // ignored.
 813                 span_bug!(span, "aliasability violation for static `{}`", prefix)
 814             }
 815             mc::AliasableBorrowed => {
 816                 let mut e = struct_span_err!(
 817                     self.tcx.sess, span, E0389,
 818                     "{} in a `&` reference", prefix);
 819                 e.span_label(span, &"assignment into an immutable reference");
 820                 if let Some(nid) = cmt.get_arg_if_immutable(&self.tcx.hir) {
 821                     self.immutable_argument_should_be_mut(nid, &mut e);
 822                 }
 823                 e
 824             }
 825         };
 826
 827         if is_closure {
 828             err.help("closures behind references must be called via `&mut`");
 829         }
 830         err.emit();
 831     }
 832
 833     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
 834     fn suggest_mut_for_immutable(&self, pty: &hir::Ty) -> Option<String> {
 835         // Check wether the argument is an immutable reference
 836         if let hir::TyRptr(lifetime, hir::MutTy {
 837             mutbl: hir::Mutability::MutImmutable,
 838             ref ty
 839         }) = pty.node {
 840             // Account for existing lifetimes when generating the message
 841             if !lifetime.is_elided() {
 842                 if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(ty.span) {
 843                     if let Ok(lifetime_snippet) = self.tcx.sess.codemap()
 844                         .span_to_snippet(lifetime.span) {
 845                             return Some(format!("use `&{} mut {}` here to make mutable",
 846                                                 lifetime_snippet,
 847                                                 snippet));
 848                     }
 849                 }
 850             } else if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(pty.span) {
 851                 if snippet.starts_with("&") {
 852                     return Some(format!("use `{}` here to make mutable",
 853                                         snippet.replace("&", "&mut ")));
 854                 }
 855             } else {
 856                 bug!("couldn't find a snippet for span: {:?}", pty.span);
 857             }
 858         }
 859         None
 860     }
 861
 862     fn immutable_argument_should_be_mut(&self, nid: ast::NodeId, db: &mut DiagnosticBuilder) {
 863         let parent = self.tcx.hir.get_parent_node(nid);
 864         let parent_node = self.tcx.hir.get(parent);
 865
 866         // The parent node is like a fn
 867         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
 868             // `nid`'s parent's `Body`
 869             let fn_body = self.tcx.hir.body(fn_like.body());
 870             // Get the position of `nid` in the arguments list
 871             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == nid);
 872             if let Some(i) = arg_pos {
 873                 // The argument's `Ty`
 874                 let arg_ty = &fn_like.decl().inputs[i];
 875                 if let Some(msg) = self.suggest_mut_for_immutable(&arg_ty) {
 876                     db.span_label(arg_ty.span, &msg);
 877                 }
 878             }
 879         }
 880     }
 881
 882     fn report_out_of_scope_escaping_closure_capture(&self,
 883                                                     err: &BckError<'tcx>,
 884                                                     capture_span: Span)
 885     {
 886         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
 887
 888         let suggestion =
 889             match self.tcx.sess.codemap().span_to_snippet(err.span) {
 890                 Ok(string) => format!("move {}", string),
 891                 Err(_) => format!("move |<args>| <body>")
 892             };
 893
 894         struct_span_err!(self.tcx.sess, err.span, E0373,
 895                          "closure may outlive the current function, \
 896                           but it borrows {}, \
 897                           which is owned by the current function",
 898                          cmt_path_or_string)
 899             .span_label(capture_span,
 900                        &format!("{} is borrowed here",
 901                                 cmt_path_or_string))
 902             .span_label(err.span,
 903                        &format!("may outlive borrowed value {}",
 904                                 cmt_path_or_string))
 905             .span_suggestion(err.span,
 906                              &format!("to force the closure to take ownership of {} \
 907                                        (and any other referenced variables), \
 908                                        use the `move` keyword, as shown:",
 909                                        cmt_path_or_string),
 910                              suggestion)
 911             .emit();
 912     }
 913
 914     fn region_end_span(&self, region: &'tcx ty::Region) -> Option<Span> {
 915         match *region {
 916             ty::ReScope(scope) => {
 917                 match scope.span(&self.tcx.region_maps, &self.tcx.hir) {
 918                     Some(s) => {
 919                         Some(s.end_point())
 920                     }
 921                     None => {
 922                         None
 923                     }
 924                 }
 925             }
 926             _ => None
 927         }
 928     }
 929
 930     pub fn note_and_explain_bckerr(&self, db: &mut DiagnosticBuilder, err: BckError<'tcx>) {
 931         let error_span = err.span.clone();
 932         match err.code {
 933             err_mutbl => self.note_and_explain_mutbl_error(db, &err, &error_span),
 934             err_out_of_scope(super_scope, sub_scope, cause) => {
 935                 let (value_kind, value_msg) = match err.cmt.cat {
 936                     mc::Categorization::Rvalue(..) =>
 937                         ("temporary value", "temporary value created here"),
 938                     _ =>
 939                         ("borrowed value", "borrow occurs here")
 940                 };
 941
 942                 let is_closure = match cause {
 943                     euv::ClosureCapture(s) => {
 944                         // The primary span starts out as the closure creation point.
 945                         // Change the primary span here to highlight the use of the variable
 946                         // in the closure, because it seems more natural. Highlight
 947                         // closure creation point as a secondary span.
 948                         match db.span.primary_span() {
 949                             Some(primary) => {
 950                                 db.span = MultiSpan::from_span(s);
 951                                 db.span_label(primary, &format!("capture occurs here"));
 952                                 db.span_label(s, &"does not live long enough");
 953                                 true
 954                             }
 955                             None => false
 956                         }
 957                     }
 958                     _ => {
 959                         db.span_label(error_span, &"does not live long enough");
 960                         false
 961                     }
 962                 };
 963
 964                 let sub_span = self.region_end_span(sub_scope);
 965                 let super_span = self.region_end_span(super_scope);
 966
 967                 match (sub_span, super_span) {
 968                     (Some(s1), Some(s2)) if s1 == s2 => {
 969                         if !is_closure {
 970                             db.span = MultiSpan::from_span(s1);
 971                             db.span_label(error_span, &value_msg);
 972                             let msg = match opt_loan_path(&err.cmt) {
 973                                 None => value_kind.to_string(),
 974                                 Some(lp) => {
 975                                     format!("`{}`", self.loan_path_to_string(&lp))
 976                                 }
 977                             };
 978                             db.span_label(s1,
 979                                           &format!("{} dropped here while still borrowed", msg));
 980                         } else {
 981                             db.span_label(s1, &format!("{} dropped before borrower", value_kind));
 982                         }
 983                         db.note("values in a scope are dropped in the opposite order \
 984                                 they are created");
 985                     }
 986                     (Some(s1), Some(s2)) if !is_closure => {
 987                         db.span = MultiSpan::from_span(s2);
 988                         db.span_label(error_span, &value_msg);
 989                         let msg = match opt_loan_path(&err.cmt) {
 990                             None => value_kind.to_string(),
 991                             Some(lp) => {
 992                                 format!("`{}`", self.loan_path_to_string(&lp))
 993                             }
 994                         };
 995                         db.span_label(s2, &format!("{} dropped here while still borrowed", msg));
 996                         db.span_label(s1, &format!("{} needs to live until here", value_kind));
 997                     }
 998                     _ => {
 999                         match sub_span {
1000                             Some(s) => {
1001                                 db.span_label(s, &format!("{} needs to live until here",
1002                                                           value_kind));
1003                             }
1004                             None => {
1005                                 self.tcx.note_and_explain_region(
1006                                     db,
1007                                     "borrowed value must be valid for ",
1008                                     sub_scope,
1009                                     "...");
1010                             }
1011                         }
1012                         match super_span {
1013                             Some(s) => {
1014                                 db.span_label(s, &format!("{} only lives until here", value_kind));
1015                             }
1016                             None => {
1017                                 self.tcx.note_and_explain_region(
1018                                     db,
1019                                     "...but borrowed value is only valid for ",
1020                                     super_scope,
1021                                     "");
1022                             }
1023                         }
1024                     }
1025                 }
1026
1027                 if let Some(_) = statement_scope_span(self.tcx, super_scope) {
1028                     db.note("consider using a `let` binding to increase its lifetime");
1029                 }
1030
1031
1032
1033                 match err.cmt.cat {
1034                     mc::Categorization::Rvalue(r, or) if r != or => {
1035                         db.note("\
1036 before rustc 1.16, this temporary lived longer - see issue #39283 \
1037 (https://github.com/rust-lang/rust/issues/39283)");
1038                     }
1039                     _ => {}
1040                 }
1041             }
1042
1043             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1044                 let descr = match opt_loan_path(&err.cmt) {
1045                     Some(lp) => {
1046                         format!("`{}`", self.loan_path_to_string(&lp))
1047                     }
1048                     None => self.cmt_to_string(&err.cmt),
1049                 };
1050                 self.tcx.note_and_explain_region(
1051                     db,
1052                     &format!("{} would have to be valid for ",
1053                             descr),
1054                     loan_scope,
1055                     "...");
1056                 self.tcx.note_and_explain_region(
1057                     db,
1058                     &format!("...but {} is only valid for ", descr),
1059                     ptr_scope,
1060                     "");
1061             }
1062         }
1063     }
1064
1065     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1066                                     error_span: &Span) {
1067         match err.cmt.note {
1068             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1069                 // If this is an `Fn` closure, it simply can't mutate upvars.
1070                 // If it's an `FnMut` closure, the original variable was declared immutable.
1071                 // We need to determine which is the case here.
1072                 let kind = match err.cmt.upvar().unwrap().cat {
1073                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1074                     _ => bug!()
1075                 };
1076                 if kind == ty::ClosureKind::Fn {
1077                     db.span_help(self.tcx.hir.span(upvar_id.closure_expr_id),
1078                                  "consider changing this closure to take \
1079                                  self by mutable reference");
1080                 }
1081             }
1082             _ => {
1083                 if let Categorization::Deref(..) = err.cmt.cat {
1084                     db.span_label(*error_span, &"cannot borrow as mutable");
1085                     if let Some(local_id) = err.cmt.get_arg_if_immutable(&self.tcx.hir) {
1086                         self.immutable_argument_should_be_mut(local_id, db);
1087                     } else if let Categorization::Deref(ref inner_cmt, ..) = err.cmt.cat {
1088                         if let Categorization::Local(local_id) = inner_cmt.cat {
1089                             self.immutable_argument_should_be_mut(local_id, db);
1090                         }
1091                     }
1092                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1093                     let span = self.tcx.hir.span(local_id);
1094                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1095                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1096                             db.span_label(*error_span, &format!("cannot reborrow mutably"));
1097                             db.span_label(*error_span, &format!("try removing `&mut` here"));
1098                         } else {
1099                             if snippet.starts_with("ref ") {
1100                                 db.span_label(span, &format!("use `{}` here to make mutable",
1101                                                              snippet.replace("ref ", "ref mut ")));
1102                             } else if snippet != "self" {
1103                                 db.span_label(span,
1104                                               &format!("use `mut {}` here to make mutable",
1105                                                        snippet));
1106                             }
1107                             db.span_label(*error_span, &format!("cannot borrow mutably"));
1108                         }
1109                     } else {
1110                         db.span_label(*error_span, &format!("cannot borrow mutably"));
1111                     }
1112                 }
1113             }
1114         }
1115     }
1116     pub fn append_loan_path_to_string(&self,
1117                                       loan_path: &LoanPath<'tcx>,
1118                                       out: &mut String) {
1119         match loan_path.kind {
1120             LpUpvar(ty::UpvarId{ var_id: id, closure_expr_id: _ }) |
1121             LpVar(id) => {
1122                 out.push_str(&self.tcx.local_var_name_str(id));
1123             }
1124
1125             LpDowncast(ref lp_base, variant_def_id) => {
1126                 out.push('(');
1127                 self.append_loan_path_to_string(&lp_base, out);
1128                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1129                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1130                 out.push(')');
1131             }
1132
1133             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1134                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1135                 match fname {
1136                     mc::NamedField(fname) => {
1137                         out.push('.');
1138                         out.push_str(&fname.as_str());
1139                     }
1140                     mc::PositionalField(idx) => {
1141                         out.push('.');
1142                         out.push_str(&idx.to_string());
1143                     }
1144                 }
1145             }
1146
1147             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement(..))) => {
1148                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1149                 out.push_str("[..]");
1150             }
1151
1152             LpExtend(ref lp_base, _, LpDeref(_)) => {
1153                 out.push('*');
1154                 self.append_loan_path_to_string(&lp_base, out);
1155             }
1156         }
1157     }
1158
1159     pub fn append_autoderefd_loan_path_to_string(&self,
1160                                                  loan_path: &LoanPath<'tcx>,
1161                                                  out: &mut String) {
1162         match loan_path.kind {
1163             LpExtend(ref lp_base, _, LpDeref(_)) => {
1164                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1165                 // rules would normally allow users to omit the `*x`.
1166                 // So just serialize such paths to `x.f` or x[3]` respectively.
1167                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1168             }
1169
1170             LpDowncast(ref lp_base, variant_def_id) => {
1171                 out.push('(');
1172                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1173                 out.push(':');
1174                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1175                 out.push(')');
1176             }
1177
1178             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1179                 self.append_loan_path_to_string(loan_path, out)
1180             }
1181         }
1182     }
1183
1184     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1185         let mut result = String::new();
1186         self.append_loan_path_to_string(loan_path, &mut result);
1187         result
1188     }
1189
1190     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1191         cmt.descriptive_string(self.tcx)
1192     }
1193
1194     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1195         match opt_loan_path(cmt) {
1196             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1197             None => self.cmt_to_string(cmt),
1198         }
1199     }
1200 }
1201
1202 fn statement_scope_span(tcx: TyCtxt, region: &ty::Region) -> Option<Span> {
1203     match *region {
1204         ty::ReScope(scope) => {
1205             match tcx.hir.find(scope.node_id(&tcx.region_maps)) {
1206                 Some(hir_map::NodeStmt(stmt)) => Some(stmt.span),
1207                 _ => None
1208             }
1209         }
1210         _ => None
1211     }
1212 }
1213
1214 impl BitwiseOperator for LoanDataFlowOperator {
1215     #[inline]
1216     fn join(&self, succ: usize, pred: usize) -> usize {
1217         succ | pred // loans from both preds are in scope
1218     }
1219 }
1220
1221 impl DataFlowOperator for LoanDataFlowOperator {
1222     #[inline]
1223     fn initial_value(&self) -> bool {
1224         false // no loans in scope by default
1225     }
1226 }
1227
1228 impl<'tcx> fmt::Debug for InteriorKind {
1229     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1230         match *self {
1231             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1232             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1233             InteriorElement(..) => write!(f, "[]"),
1234         }
1235     }
1236 }
1237
1238 impl<'tcx> fmt::Debug for Loan<'tcx> {
1239     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1240         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1241                self.index,
1242                self.loan_path,
1243                self.kind,
1244                self.gen_scope,
1245                self.kill_scope,
1246                self.restricted_paths)
1247     }
1248 }
1249
1250 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1251     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1252         match self.kind {
1253             LpVar(id) => {
1254                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1255             }
1256
1257             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1258                 let s = ty::tls::with(|tcx| tcx.hir.node_to_string(var_id));
1259                 write!(f, "$({} captured by id={})", s, closure_expr_id)
1260             }
1261
1262             LpDowncast(ref lp, variant_def_id) => {
1263                 let variant_str = if variant_def_id.is_local() {
1264                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1265                 } else {
1266                     format!("{:?}", variant_def_id)
1267                 };
1268                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1269             }
1270
1271             LpExtend(ref lp, _, LpDeref(_)) => {
1272                 write!(f, "{:?}.*", lp)
1273             }
1274
1275             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1276                 write!(f, "{:?}.{:?}", lp, interior)
1277             }
1278         }
1279     }
1280 }
1281
1282 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1283     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1284         match self.kind {
1285             LpVar(id) => {
1286                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1287             }
1288
1289             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1290                 let s = ty::tls::with(|tcx| tcx.hir.node_to_user_string(var_id));
1291                 write!(f, "$({} captured by closure)", s)
1292             }
1293
1294             LpDowncast(ref lp, variant_def_id) => {
1295                 let variant_str = if variant_def_id.is_local() {
1296                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1297                 } else {
1298                     format!("{:?}", variant_def_id)
1299                 };
1300                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1301             }
1302
1303             LpExtend(ref lp, _, LpDeref(_)) => {
1304                 write!(f, "{}.*", lp)
1305             }
1306
1307             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1308                 write!(f, "{}.{:?}", lp, interior)
1309             }
1310         }
1311     }
1312 }