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::free_region::FreeRegionMap;
  36 use rustc::middle::mem_categorization as mc;
  37 use rustc::middle::mem_categorization::Categorization;
  38 use rustc::middle::region;
  39 use rustc::ty::{self, TyCtxt};
  40
  41 use std::fmt;
  42 use std::mem;
  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, FnKind, NestedVisitorMap};
  51
  52 pub mod check_loans;
  53
  54 pub mod gather_loans;
  55
  56 pub mod move_data;
  57
  58 mod mir;
  59
  60 #[derive(Clone, Copy)]
  61 pub struct LoanDataFlowOperator;
  62
  63 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  64
  65 impl<'a, 'tcx> Visitor<'tcx> for BorrowckCtxt<'a, 'tcx> {
  66     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  67         NestedVisitorMap::OnlyBodies(&self.tcx.map)
  68     }
  69
  70     fn visit_fn(&mut self, fk: FnKind<'tcx>, fd: &'tcx hir::FnDecl,
  71                 b: hir::BodyId, s: Span, id: ast::NodeId) {
  72         match fk {
  73             FnKind::ItemFn(..) |
  74             FnKind::Method(..) => {
  75                 self.with_temp_region_map(id, |this| {
  76                     borrowck_fn(this, fk, fd, b, s, id, fk.attrs())
  77                 });
  78             }
  79
  80             FnKind::Closure(..) => {
  81                 borrowck_fn(self, fk, fd, b, s, id, fk.attrs());
  82             }
  83         }
  84     }
  85
  86     fn visit_item(&mut self, item: &'tcx hir::Item) {
  87         borrowck_item(self, item);
  88     }
  89
  90     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem) {
  91         if let hir::TraitItemKind::Const(_, Some(expr)) = ti.node {
  92             gather_loans::gather_loans_in_static_initializer(self, expr);
  93         }
  94         intravisit::walk_trait_item(self, ti);
  95     }
  96
  97     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem) {
  98         if let hir::ImplItemKind::Const(_, expr) = ii.node {
  99             gather_loans::gather_loans_in_static_initializer(self, expr);
 100         }
 101         intravisit::walk_impl_item(self, ii);
 102     }
 103 }
 104
 105 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 106     let mut bccx = BorrowckCtxt {
 107         tcx: tcx,
 108         free_region_map: FreeRegionMap::new(),
 109         stats: BorrowStats {
 110             loaned_paths_same: 0,
 111             loaned_paths_imm: 0,
 112             stable_paths: 0,
 113             guaranteed_paths: 0
 114         }
 115     };
 116
 117     tcx.visit_all_item_likes_in_krate(DepNode::BorrowCheck, &mut bccx.as_deep_visitor());
 118
 119     if tcx.sess.borrowck_stats() {
 120         println!("--- borrowck stats ---");
 121         println!("paths requiring guarantees: {}",
 122                  bccx.stats.guaranteed_paths);
 123         println!("paths requiring loans     : {}",
 124                  make_stat(&bccx, bccx.stats.loaned_paths_same));
 125         println!("paths requiring imm loans : {}",
 126                  make_stat(&bccx, bccx.stats.loaned_paths_imm));
 127         println!("stable paths              : {}",
 128                  make_stat(&bccx, bccx.stats.stable_paths));
 129     }
 130
 131     fn make_stat(bccx: &BorrowckCtxt, stat: usize) -> String {
 132         let total = bccx.stats.guaranteed_paths as f64;
 133         let perc = if total == 0.0 { 0.0 } else { stat as f64 * 100.0 / total };
 134         format!("{} ({:.0}%)", stat, perc)
 135     }
 136 }
 137
 138 fn borrowck_item<'a, 'tcx>(this: &mut BorrowckCtxt<'a, 'tcx>, item: &'tcx hir::Item) {
 139     // Gather loans for items. Note that we don't need
 140     // to check loans for single expressions. The check
 141     // loan step is intended for things that have a data
 142     // flow dependent conditions.
 143     match item.node {
 144         hir::ItemStatic(.., ex) |
 145         hir::ItemConst(_, ex) => {
 146             gather_loans::gather_loans_in_static_initializer(this, ex);
 147         }
 148         _ => { }
 149     }
 150
 151     intravisit::walk_item(this, item);
 152 }
 153
 154 /// Collection of conclusions determined via borrow checker analyses.
 155 pub struct AnalysisData<'a, 'tcx: 'a> {
 156     pub all_loans: Vec<Loan<'tcx>>,
 157     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
 158     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
 159 }
 160
 161 fn borrowck_fn<'a, 'tcx>(this: &mut BorrowckCtxt<'a, 'tcx>,
 162                          fk: FnKind<'tcx>,
 163                          decl: &'tcx hir::FnDecl,
 164                          body_id: hir::BodyId,
 165                          sp: Span,
 166                          id: ast::NodeId,
 167                          attributes: &[ast::Attribute]) {
 168     debug!("borrowck_fn(id={})", id);
 169
 170     let body = this.tcx.map.body(body_id);
 171
 172     if attributes.iter().any(|item| item.check_name("rustc_mir_borrowck")) {
 173         this.with_temp_region_map(id, |this| {
 174             mir::borrowck_mir(this, id, attributes)
 175         });
 176     }
 177
 178     let cfg = cfg::CFG::new(this.tcx, &body.value);
 179     let AnalysisData { all_loans,
 180                        loans: loan_dfcx,
 181                        move_data: flowed_moves } =
 182         build_borrowck_dataflow_data(this, &cfg, body_id);
 183
 184     move_data::fragments::instrument_move_fragments(&flowed_moves.move_data,
 185                                                     this.tcx,
 186                                                     sp,
 187                                                     id);
 188     move_data::fragments::build_unfragmented_map(this,
 189                                                  &flowed_moves.move_data,
 190                                                  id);
 191
 192     check_loans::check_loans(this, &loan_dfcx, &flowed_moves, &all_loans[..], body);
 193
 194     intravisit::walk_fn(this, fk, decl, body_id, sp, id);
 195 }
 196
 197 fn build_borrowck_dataflow_data<'a, 'tcx>(this: &mut BorrowckCtxt<'a, 'tcx>,
 198                                           cfg: &cfg::CFG,
 199                                           body_id: hir::BodyId)
 200                                           -> AnalysisData<'a, 'tcx>
 201 {
 202     // Check the body of fn items.
 203     let tcx = this.tcx;
 204     let body = tcx.map.body(body_id);
 205     let id_range = {
 206         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.map);
 207         visitor.visit_body(body);
 208         visitor.result()
 209     };
 210     let (all_loans, move_data) =
 211         gather_loans::gather_loans_in_fn(this, body_id);
 212
 213     let mut loan_dfcx =
 214         DataFlowContext::new(this.tcx,
 215                              "borrowck",
 216                              Some(body),
 217                              cfg,
 218                              LoanDataFlowOperator,
 219                              id_range,
 220                              all_loans.len());
 221     for (loan_idx, loan) in all_loans.iter().enumerate() {
 222         loan_dfcx.add_gen(loan.gen_scope.node_id(&tcx.region_maps), loan_idx);
 223         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 224                            loan.kill_scope.node_id(&tcx.region_maps), loan_idx);
 225     }
 226     loan_dfcx.add_kills_from_flow_exits(cfg);
 227     loan_dfcx.propagate(cfg, body);
 228
 229     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 230                                                       this.tcx,
 231                                                       cfg,
 232                                                       id_range,
 233                                                       body);
 234
 235     AnalysisData { all_loans: all_loans,
 236                    loans: loan_dfcx,
 237                    move_data:flowed_moves }
 238 }
 239
 240 /// Accessor for introspective clients inspecting `AnalysisData` and
 241 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 242 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 243     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 244     body: hir::BodyId,
 245     cfg: &cfg::CFG)
 246     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 247 {
 248
 249     let mut bccx = BorrowckCtxt {
 250         tcx: tcx,
 251         free_region_map: FreeRegionMap::new(),
 252         stats: BorrowStats {
 253             loaned_paths_same: 0,
 254             loaned_paths_imm: 0,
 255             stable_paths: 0,
 256             guaranteed_paths: 0
 257         }
 258     };
 259
 260     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, cfg, body);
 261     (bccx, dataflow_data)
 262 }
 263
 264 // ----------------------------------------------------------------------
 265 // Type definitions
 266
 267 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 268     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 269
 270     // Hacky. As we visit various fns, we have to load up the
 271     // free-region map for each one. This map is computed by during
 272     // typeck for each fn item and stored -- closures just use the map
 273     // from the fn item that encloses them. Since we walk the fns in
 274     // order, we basically just overwrite this field as we enter a fn
 275     // item and restore it afterwards in a stack-like fashion. Then
 276     // the borrow checking code can assume that `free_region_map` is
 277     // always the correct map for the current fn. Feels like it'd be
 278     // better to just recompute this, rather than store it, but it's a
 279     // bit of a pain to factor that code out at the moment.
 280     free_region_map: FreeRegionMap,
 281
 282     // Statistics:
 283     stats: BorrowStats
 284 }
 285
 286 #[derive(Clone)]
 287 struct BorrowStats {
 288     loaned_paths_same: usize,
 289     loaned_paths_imm: usize,
 290     stable_paths: usize,
 291     guaranteed_paths: usize
 292 }
 293
 294 ///////////////////////////////////////////////////////////////////////////
 295 // Loans and loan paths
 296
 297 /// Record of a loan that was issued.
 298 pub struct Loan<'tcx> {
 299     index: usize,
 300     loan_path: Rc<LoanPath<'tcx>>,
 301     kind: ty::BorrowKind,
 302     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 303
 304     /// gen_scope indicates where loan is introduced. Typically the
 305     /// loan is introduced at the point of the borrow, but in some
 306     /// cases, notably method arguments, the loan may be introduced
 307     /// only later, once it comes into scope.  See also
 308     /// `GatherLoanCtxt::compute_gen_scope`.
 309     gen_scope: region::CodeExtent,
 310
 311     /// kill_scope indicates when the loan goes out of scope.  This is
 312     /// either when the lifetime expires or when the local variable
 313     /// which roots the loan-path goes out of scope, whichever happens
 314     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 315     kill_scope: region::CodeExtent,
 316     span: Span,
 317     cause: euv::LoanCause,
 318 }
 319
 320 impl<'tcx> Loan<'tcx> {
 321     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 322         self.loan_path.clone()
 323     }
 324 }
 325
 326 #[derive(Eq)]
 327 pub struct LoanPath<'tcx> {
 328     kind: LoanPathKind<'tcx>,
 329     ty: ty::Ty<'tcx>,
 330 }
 331
 332 impl<'tcx> PartialEq for LoanPath<'tcx> {
 333     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 334         self.kind == that.kind
 335     }
 336 }
 337
 338 impl<'tcx> Hash for LoanPath<'tcx> {
 339     fn hash<H: Hasher>(&self, state: &mut H) {
 340         self.kind.hash(state);
 341     }
 342 }
 343
 344 #[derive(PartialEq, Eq, Hash, Debug)]
 345 pub enum LoanPathKind<'tcx> {
 346     LpVar(ast::NodeId),                         // `x` in README.md
 347     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 348     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 349     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 350 }
 351
 352 impl<'tcx> LoanPath<'tcx> {
 353     fn new(kind: LoanPathKind<'tcx>, ty: ty::Ty<'tcx>) -> LoanPath<'tcx> {
 354         LoanPath { kind: kind, ty: ty }
 355     }
 356
 357     fn to_type(&self) -> ty::Ty<'tcx> { self.ty }
 358 }
 359
 360 // FIXME (pnkfelix): See discussion here
 361 // https://github.com/pnkfelix/rust/commit/
 362 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 363 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 364
 365 // A local, "cleaned" version of `mc::InteriorKind` that drops
 366 // information that is not relevant to loan-path analysis. (In
 367 // particular, the distinction between how precisely an array-element
 368 // is tracked is irrelevant here.)
 369 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 370 pub enum InteriorKind {
 371     InteriorField(mc::FieldName),
 372     InteriorElement(mc::ElementKind),
 373 }
 374
 375 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 376 impl ToInteriorKind for mc::InteriorKind {
 377     fn cleaned(self) -> InteriorKind {
 378         match self {
 379             mc::InteriorField(name) => InteriorField(name),
 380             mc::InteriorElement(_, elem_kind) => InteriorElement(elem_kind),
 381         }
 382     }
 383 }
 384
 385 // This can be:
 386 // - a pointer dereference (`*LV` in README.md)
 387 // - a field reference, with an optional definition of the containing
 388 //   enum variant (`LV.f` in README.md)
 389 // `DefId` is present when the field is part of struct that is in
 390 // a variant of an enum. For instance in:
 391 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 392 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 393 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 394 pub enum LoanPathElem<'tcx> {
 395     LpDeref(mc::PointerKind<'tcx>),
 396     LpInterior(Option<DefId>, InteriorKind),
 397 }
 398
 399 pub fn closure_to_block(closure_id: ast::NodeId,
 400                         tcx: TyCtxt) -> ast::NodeId {
 401     match tcx.map.get(closure_id) {
 402         hir_map::NodeExpr(expr) => match expr.node {
 403             hir::ExprClosure(.., body_id, _) => {
 404                 body_id.node_id
 405             }
 406             _ => {
 407                 bug!("encountered non-closure id: {}", closure_id)
 408             }
 409         },
 410         _ => bug!("encountered non-expr id: {}", closure_id)
 411     }
 412 }
 413
 414 impl<'a, 'tcx> LoanPath<'tcx> {
 415     pub fn kill_scope(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> region::CodeExtent {
 416         match self.kind {
 417             LpVar(local_id) => tcx.region_maps.var_scope(local_id),
 418             LpUpvar(upvar_id) => {
 419                 let block_id = closure_to_block(upvar_id.closure_expr_id, tcx);
 420                 tcx.region_maps.node_extent(block_id)
 421             }
 422             LpDowncast(ref base, _) |
 423             LpExtend(ref base, ..) => base.kill_scope(tcx),
 424         }
 425     }
 426
 427     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 428         match (&self.kind, &other.kind) {
 429             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 430              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 431                 if id == id2 && opt_variant_id == opt_variant_id2 {
 432                     base.has_fork(&base2)
 433                 } else {
 434                     true
 435                 },
 436             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 437             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 438             _ => false,
 439         }
 440     }
 441
 442     fn depth(&self) -> usize {
 443         match self.kind {
 444             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 445             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 446             _ => 0,
 447         }
 448     }
 449
 450     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 451         match (&self.kind, &other.kind) {
 452             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 453              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 454                 if id == id2 && opt_variant_id == opt_variant_id2 {
 455                     base.common(&base2).map(|x| {
 456                         let xd = x.depth();
 457                         if base.depth() == xd && base2.depth() == xd {
 458                             LoanPath {
 459                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 460                                 ty: self.ty,
 461                             }
 462                         } else {
 463                             x
 464                         }
 465                     })
 466                 } else {
 467                     base.common(&base2)
 468                 }
 469             }
 470             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 471             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 472             (&LpVar(id), &LpVar(id2)) => {
 473                 if id == id2 {
 474                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 475                 } else {
 476                     None
 477                 }
 478             }
 479             (&LpUpvar(id), &LpUpvar(id2)) => {
 480                 if id == id2 {
 481                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 482                 } else {
 483                     None
 484                 }
 485             }
 486             _ => None,
 487         }
 488     }
 489 }
 490
 491 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 492     //! Computes the `LoanPath` (if any) for a `cmt`.
 493     //! Note that this logic is somewhat duplicated in
 494     //! the method `compute()` found in `gather_loans::restrictions`,
 495     //! which allows it to share common loan path pieces as it
 496     //! traverses the CMT.
 497
 498     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 499
 500     match cmt.cat {
 501         Categorization::Rvalue(..) |
 502         Categorization::StaticItem => {
 503             None
 504         }
 505
 506         Categorization::Local(id) => {
 507             Some(new_lp(LpVar(id)))
 508         }
 509
 510         Categorization::Upvar(mc::Upvar { id, .. }) => {
 511             Some(new_lp(LpUpvar(id)))
 512         }
 513
 514         Categorization::Deref(ref cmt_base, _, pk) => {
 515             opt_loan_path(cmt_base).map(|lp| {
 516                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 517             })
 518         }
 519
 520         Categorization::Interior(ref cmt_base, ik) => {
 521             opt_loan_path(cmt_base).map(|lp| {
 522                 let opt_variant_id = match cmt_base.cat {
 523                     Categorization::Downcast(_, did) =>  Some(did),
 524                     _ => None
 525                 };
 526                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 527             })
 528         }
 529
 530         Categorization::Downcast(ref cmt_base, variant_def_id) =>
 531             opt_loan_path(cmt_base)
 532             .map(|lp| {
 533                 new_lp(LpDowncast(lp, variant_def_id))
 534             }),
 535
 536     }
 537 }
 538
 539 ///////////////////////////////////////////////////////////////////////////
 540 // Errors
 541
 542 // Errors that can occur
 543 #[derive(PartialEq)]
 544 pub enum bckerr_code<'tcx> {
 545     err_mutbl,
 546     /// superscope, subscope, loan cause
 547     err_out_of_scope(&'tcx ty::Region, &'tcx ty::Region, euv::LoanCause),
 548     err_borrowed_pointer_too_short(&'tcx ty::Region, &'tcx ty::Region), // loan, ptr
 549 }
 550
 551 // Combination of an error code and the categorization of the expression
 552 // that caused it
 553 #[derive(PartialEq)]
 554 pub struct BckError<'tcx> {
 555     span: Span,
 556     cause: AliasableViolationKind,
 557     cmt: mc::cmt<'tcx>,
 558     code: bckerr_code<'tcx>
 559 }
 560
 561 #[derive(Copy, Clone, Debug, PartialEq)]
 562 pub enum AliasableViolationKind {
 563     MutabilityViolation,
 564     BorrowViolation(euv::LoanCause)
 565 }
 566
 567 #[derive(Copy, Clone, Debug)]
 568 pub enum MovedValueUseKind {
 569     MovedInUse,
 570     MovedInCapture,
 571 }
 572
 573 ///////////////////////////////////////////////////////////////////////////
 574 // Misc
 575
 576 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 577     fn with_temp_region_map<F>(&mut self, id: ast::NodeId, f: F)
 578         where F: for <'b> FnOnce(&'b mut BorrowckCtxt<'a, 'tcx>)
 579     {
 580         let new_free_region_map = self.tcx.free_region_map(id);
 581         let old_free_region_map = mem::replace(&mut self.free_region_map, new_free_region_map);
 582         f(self);
 583         self.free_region_map = old_free_region_map;
 584     }
 585
 586     pub fn is_subregion_of(&self, r_sub: &'tcx ty::Region, r_sup: &'tcx ty::Region)
 587                            -> bool
 588     {
 589         self.free_region_map.is_subregion_of(self.tcx, r_sub, r_sup)
 590     }
 591
 592     pub fn report(&self, err: BckError<'tcx>) {
 593         // Catch and handle some particular cases.
 594         match (&err.code, &err.cause) {
 595             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 596              &BorrowViolation(euv::ClosureCapture(span))) |
 597             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 598              &BorrowViolation(euv::ClosureCapture(span))) => {
 599                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 600             }
 601             _ => { }
 602         }
 603
 604         // General fallback.
 605         let span = err.span.clone();
 606         let mut db = self.struct_span_err(
 607             err.span,
 608             &self.bckerr_to_string(&err));
 609         self.note_and_explain_bckerr(&mut db, err, span);
 610         db.emit();
 611     }
 612
 613     pub fn report_use_of_moved_value(&self,
 614                                      use_span: Span,
 615                                      use_kind: MovedValueUseKind,
 616                                      lp: &LoanPath<'tcx>,
 617                                      the_move: &move_data::Move,
 618                                      moved_lp: &LoanPath<'tcx>,
 619                                      _param_env: &ty::ParameterEnvironment<'tcx>) {
 620         let (verb, verb_participle) = match use_kind {
 621             MovedInUse => ("use", "used"),
 622             MovedInCapture => ("capture", "captured"),
 623         };
 624
 625         let (_ol, _moved_lp_msg, mut err) = match the_move.kind {
 626             move_data::Declared => {
 627                 // If this is an uninitialized variable, just emit a simple warning
 628                 // and return.
 629                 struct_span_err!(
 630                     self.tcx.sess, use_span, E0381,
 631                     "{} of possibly uninitialized variable: `{}`",
 632                     verb,
 633                     self.loan_path_to_string(lp))
 634                 .span_label(use_span, &format!("use of possibly uninitialized `{}`",
 635                     self.loan_path_to_string(lp)))
 636                 .emit();
 637                 return;
 638             }
 639             _ => {
 640                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 641                 // normally generate a rather confusing message:
 642                 //
 643                 //     error: use of moved value: `x.b`
 644                 //     note: `x.a` moved here...
 645                 //
 646                 // What we want to do instead is get the 'common ancestor' of the two moves and
 647                 // use that for most of the message instead, giving is something like this:
 648                 //
 649                 //     error: use of moved value: `x`
 650                 //     note: `x` moved here (through moving `x.a`)...
 651
 652                 let common = moved_lp.common(lp);
 653                 let has_common = common.is_some();
 654                 let has_fork = moved_lp.has_fork(lp);
 655                 let (nl, ol, moved_lp_msg) =
 656                     if has_fork && has_common {
 657                         let nl = self.loan_path_to_string(&common.unwrap());
 658                         let ol = nl.clone();
 659                         let moved_lp_msg = format!(" (through moving `{}`)",
 660                                                    self.loan_path_to_string(moved_lp));
 661                         (nl, ol, moved_lp_msg)
 662                     } else {
 663                         (self.loan_path_to_string(lp),
 664                          self.loan_path_to_string(moved_lp),
 665                          String::new())
 666                     };
 667
 668                 let partial = moved_lp.depth() > lp.depth();
 669                 let msg = if !has_fork && partial { "partially " }
 670                           else if has_fork && !has_common { "collaterally "}
 671                           else { "" };
 672                 let err = struct_span_err!(
 673                     self.tcx.sess, use_span, E0382,
 674                     "{} of {}moved value: `{}`",
 675                     verb, msg, nl);
 676                 (ol, moved_lp_msg, err)}
 677         };
 678
 679         // Get type of value and span where it was previously
 680         // moved.
 681         let (move_span, move_note) = match the_move.kind {
 682             move_data::Declared => {
 683                 unreachable!();
 684             }
 685
 686             move_data::MoveExpr |
 687             move_data::MovePat =>
 688                 (self.tcx.map.span(the_move.id), ""),
 689
 690             move_data::Captured =>
 691                 (match self.tcx.map.expect_expr(the_move.id).node {
 692                     hir::ExprClosure(.., fn_decl_span) => fn_decl_span,
 693                     ref r => bug!("Captured({}) maps to non-closure: {:?}",
 694                                   the_move.id, r),
 695                 }, " (into closure)"),
 696         };
 697
 698         // Annotate the use and the move in the span. Watch out for
 699         // the case where the use and the move are the same. This
 700         // means the use is in a loop.
 701         err = if use_span == move_span {
 702             err.span_label(
 703                 use_span,
 704                 &format!("value moved{} here in previous iteration of loop",
 705                          move_note));
 706             err
 707         } else {
 708             err.span_label(use_span, &format!("value {} here after move", verb_participle))
 709                .span_label(move_span, &format!("value moved{} here", move_note));
 710             err
 711         };
 712
 713         err.note(&format!("move occurs because `{}` has type `{}`, \
 714                            which does not implement the `Copy` trait",
 715                           self.loan_path_to_string(moved_lp),
 716                           moved_lp.ty));
 717
 718         // Note: we used to suggest adding a `ref binding` or calling
 719         // `clone` but those suggestions have been removed because
 720         // they are often not what you actually want to do, and were
 721         // not considered particularly helpful.
 722
 723         err.emit();
 724     }
 725
 726     pub fn report_partial_reinitialization_of_uninitialized_structure(
 727             &self,
 728             span: Span,
 729             lp: &LoanPath<'tcx>) {
 730         span_err!(
 731             self.tcx.sess, span, E0383,
 732             "partial reinitialization of uninitialized structure `{}`",
 733             self.loan_path_to_string(lp));
 734     }
 735
 736     pub fn report_reassigned_immutable_variable(&self,
 737                                                 span: Span,
 738                                                 lp: &LoanPath<'tcx>,
 739                                                 assign:
 740                                                 &move_data::Assignment) {
 741         let mut err = struct_span_err!(
 742             self.tcx.sess, span, E0384,
 743             "re-assignment of immutable variable `{}`",
 744             self.loan_path_to_string(lp));
 745         err.span_label(span, &format!("re-assignment of immutable variable"));
 746         if span != assign.span {
 747             err.span_label(assign.span, &format!("first assignment to `{}`",
 748                                               self.loan_path_to_string(lp)));
 749         }
 750         err.emit();
 751     }
 752
 753     pub fn span_err(&self, s: Span, m: &str) {
 754         self.tcx.sess.span_err(s, m);
 755     }
 756
 757     pub fn struct_span_err<S: Into<MultiSpan>>(&self, s: S, m: &str)
 758                                               -> DiagnosticBuilder<'a> {
 759         self.tcx.sess.struct_span_err(s, m)
 760     }
 761
 762     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 763                                                          s: S,
 764                                                          msg: &str,
 765                                                          code: &str)
 766                                                          -> DiagnosticBuilder<'a> {
 767         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 768     }
 769
 770     pub fn span_err_with_code<S: Into<MultiSpan>>(&self, s: S, msg: &str, code: &str) {
 771         self.tcx.sess.span_err_with_code(s, msg, code);
 772     }
 773
 774     pub fn bckerr_to_string(&self, err: &BckError<'tcx>) -> String {
 775         match err.code {
 776             err_mutbl => {
 777                 let descr = match err.cmt.note {
 778                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 779                         self.cmt_to_string(&err.cmt)
 780                     }
 781                     _ => match opt_loan_path(&err.cmt) {
 782                         None => {
 783                             format!("{} {}",
 784                                     err.cmt.mutbl.to_user_str(),
 785                                     self.cmt_to_string(&err.cmt))
 786                         }
 787                         Some(lp) => {
 788                             format!("{} {} `{}`",
 789                                     err.cmt.mutbl.to_user_str(),
 790                                     self.cmt_to_string(&err.cmt),
 791                                     self.loan_path_to_string(&lp))
 792                         }
 793                     }
 794                 };
 795
 796                 match err.cause {
 797                     MutabilityViolation => {
 798                         format!("cannot assign to {}", descr)
 799                     }
 800                     BorrowViolation(euv::ClosureCapture(_)) => {
 801                         format!("closure cannot assign to {}", descr)
 802                     }
 803                     BorrowViolation(euv::OverloadedOperator) |
 804                     BorrowViolation(euv::AddrOf) |
 805                     BorrowViolation(euv::RefBinding) |
 806                     BorrowViolation(euv::AutoRef) |
 807                     BorrowViolation(euv::AutoUnsafe) |
 808                     BorrowViolation(euv::ForLoop) |
 809                     BorrowViolation(euv::MatchDiscriminant) => {
 810                         format!("cannot borrow {} as mutable", descr)
 811                     }
 812                     BorrowViolation(euv::ClosureInvocation) => {
 813                         span_bug!(err.span,
 814                             "err_mutbl with a closure invocation");
 815                     }
 816                 }
 817             }
 818             err_out_of_scope(..) => {
 819                 let msg = match opt_loan_path(&err.cmt) {
 820                     None => "borrowed value".to_string(),
 821                     Some(lp) => {
 822                         format!("`{}`", self.loan_path_to_string(&lp))
 823                     }
 824                 };
 825                 format!("{} does not live long enough", msg)
 826             }
 827             err_borrowed_pointer_too_short(..) => {
 828                 let descr = self.cmt_to_path_or_string(&err.cmt);
 829                 format!("lifetime of {} is too short to guarantee \
 830                          its contents can be safely reborrowed",
 831                         descr)
 832             }
 833         }
 834     }
 835
 836     pub fn report_aliasability_violation(&self,
 837                                          span: Span,
 838                                          kind: AliasableViolationKind,
 839                                          cause: mc::AliasableReason) {
 840         let mut is_closure = false;
 841         let prefix = match kind {
 842             MutabilityViolation => {
 843                 "cannot assign to data"
 844             }
 845             BorrowViolation(euv::ClosureCapture(_)) |
 846             BorrowViolation(euv::OverloadedOperator) |
 847             BorrowViolation(euv::AddrOf) |
 848             BorrowViolation(euv::AutoRef) |
 849             BorrowViolation(euv::AutoUnsafe) |
 850             BorrowViolation(euv::RefBinding) |
 851             BorrowViolation(euv::MatchDiscriminant) => {
 852                 "cannot borrow data mutably"
 853             }
 854
 855             BorrowViolation(euv::ClosureInvocation) => {
 856                 is_closure = true;
 857                 "closure invocation"
 858             }
 859
 860             BorrowViolation(euv::ForLoop) => {
 861                 "`for` loop"
 862             }
 863         };
 864
 865         let mut err = match cause {
 866             mc::AliasableOther => {
 867                 struct_span_err!(
 868                     self.tcx.sess, span, E0385,
 869                     "{} in an aliasable location", prefix)
 870             }
 871             mc::AliasableReason::UnaliasableImmutable => {
 872                 struct_span_err!(
 873                     self.tcx.sess, span, E0386,
 874                     "{} in an immutable container", prefix)
 875             }
 876             mc::AliasableClosure(id) => {
 877                 let mut err = struct_span_err!(
 878                     self.tcx.sess, span, E0387,
 879                     "{} in a captured outer variable in an `Fn` closure", prefix);
 880                 if let BorrowViolation(euv::ClosureCapture(_)) = kind {
 881                     // The aliasability violation with closure captures can
 882                     // happen for nested closures, so we know the enclosing
 883                     // closure incorrectly accepts an `Fn` while it needs to
 884                     // be `FnMut`.
 885                     span_help!(&mut err, self.tcx.map.span(id),
 886                            "consider changing this to accept closures that implement `FnMut`");
 887                 } else {
 888                     span_help!(&mut err, self.tcx.map.span(id),
 889                            "consider changing this closure to take self by mutable reference");
 890                 }
 891                 err
 892             }
 893             mc::AliasableStatic |
 894             mc::AliasableStaticMut => {
 895                 let mut err = struct_span_err!(
 896                     self.tcx.sess, span, E0388,
 897                     "{} in a static location", prefix);
 898                 err.span_label(span, &format!("cannot write data in a static definition"));
 899                 err
 900             }
 901             mc::AliasableBorrowed => {
 902                 let mut e = struct_span_err!(
 903                     self.tcx.sess, span, E0389,
 904                     "{} in a `&` reference", prefix);
 905                 e.span_label(span, &"assignment into an immutable reference");
 906                 e
 907             }
 908         };
 909
 910         if is_closure {
 911             err.help("closures behind references must be called via `&mut`");
 912         }
 913         err.emit();
 914     }
 915
 916     fn report_out_of_scope_escaping_closure_capture(&self,
 917                                                     err: &BckError<'tcx>,
 918                                                     capture_span: Span)
 919     {
 920         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
 921
 922         let suggestion =
 923             match self.tcx.sess.codemap().span_to_snippet(err.span) {
 924                 Ok(string) => format!("move {}", string),
 925                 Err(_) => format!("move |<args>| <body>")
 926             };
 927
 928         struct_span_err!(self.tcx.sess, err.span, E0373,
 929                          "closure may outlive the current function, \
 930                           but it borrows {}, \
 931                           which is owned by the current function",
 932                          cmt_path_or_string)
 933             .span_label(capture_span,
 934                        &format!("{} is borrowed here",
 935                                 cmt_path_or_string))
 936             .span_label(err.span,
 937                        &format!("may outlive borrowed value {}",
 938                                 cmt_path_or_string))
 939             .span_suggestion(err.span,
 940                              &format!("to force the closure to take ownership of {} \
 941                                        (and any other referenced variables), \
 942                                        use the `move` keyword, as shown:",
 943                                        cmt_path_or_string),
 944                              suggestion)
 945             .emit();
 946     }
 947
 948     fn region_end_span(&self, region: &'tcx ty::Region) -> Option<Span> {
 949         match *region {
 950             ty::ReScope(scope) => {
 951                 match scope.span(&self.tcx.region_maps, &self.tcx.map) {
 952                     Some(s) => {
 953                         Some(s.end_point())
 954                     }
 955                     None => {
 956                         None
 957                     }
 958                 }
 959             }
 960             _ => None
 961         }
 962     }
 963
 964     pub fn note_and_explain_bckerr(&self, db: &mut DiagnosticBuilder, err: BckError<'tcx>,
 965         error_span: Span) {
 966         match err.code {
 967             err_mutbl => self.note_and_explain_mutbl_error(db, &err, &error_span),
 968             err_out_of_scope(super_scope, sub_scope, cause) => {
 969                 let (value_kind, value_msg) = match err.cmt.cat {
 970                     mc::Categorization::Rvalue(..) =>
 971                         ("temporary value", "temporary value created here"),
 972                     _ =>
 973                         ("borrowed value", "borrow occurs here")
 974                 };
 975
 976                 let is_closure = match cause {
 977                     euv::ClosureCapture(s) => {
 978                         // The primary span starts out as the closure creation point.
 979                         // Change the primary span here to highlight the use of the variable
 980                         // in the closure, because it seems more natural. Highlight
 981                         // closure creation point as a secondary span.
 982                         match db.span.primary_span() {
 983                             Some(primary) => {
 984                                 db.span = MultiSpan::from_span(s);
 985                                 db.span_label(primary, &format!("capture occurs here"));
 986                                 db.span_label(s, &"does not live long enough");
 987                                 true
 988                             }
 989                             None => false
 990                         }
 991                     }
 992                     _ => {
 993                         db.span_label(error_span, &"does not live long enough");
 994                         false
 995                     }
 996                 };
 997
 998                 let sub_span = self.region_end_span(sub_scope);
 999                 let super_span = self.region_end_span(super_scope);
1000
1001                 match (sub_span, super_span) {
1002                     (Some(s1), Some(s2)) if s1 == s2 => {
1003                         if !is_closure {
1004                             db.span = MultiSpan::from_span(s1);
1005                             db.span_label(error_span, &value_msg);
1006                             let msg = match opt_loan_path(&err.cmt) {
1007                                 None => value_kind.to_string(),
1008                                 Some(lp) => {
1009                                     format!("`{}`", self.loan_path_to_string(&lp))
1010                                 }
1011                             };
1012                             db.span_label(s1,
1013                                           &format!("{} dropped here while still borrowed", msg));
1014                         } else {
1015                             db.span_label(s1, &format!("{} dropped before borrower", value_kind));
1016                         }
1017                         db.note("values in a scope are dropped in the opposite order \
1018                                 they are created");
1019                     }
1020                     (Some(s1), Some(s2)) if !is_closure => {
1021                         db.span = MultiSpan::from_span(s2);
1022                         db.span_label(error_span, &value_msg);
1023                         let msg = match opt_loan_path(&err.cmt) {
1024                             None => value_kind.to_string(),
1025                             Some(lp) => {
1026                                 format!("`{}`", self.loan_path_to_string(&lp))
1027                             }
1028                         };
1029                         db.span_label(s2, &format!("{} dropped here while still borrowed", msg));
1030                         db.span_label(s1, &format!("{} needs to live until here", value_kind));
1031                     }
1032                     _ => {
1033                         match sub_span {
1034                             Some(s) => {
1035                                 db.span_label(s, &format!("{} needs to live until here",
1036                                                           value_kind));
1037                             }
1038                             None => {
1039                                 self.tcx.note_and_explain_region(
1040                                     db,
1041                                     "borrowed value must be valid for ",
1042                                     sub_scope,
1043                                     "...");
1044                             }
1045                         }
1046                         match super_span {
1047                             Some(s) => {
1048                                 db.span_label(s, &format!("{} only lives until here", value_kind));
1049                             }
1050                             None => {
1051                                 self.tcx.note_and_explain_region(
1052                                     db,
1053                                     "...but borrowed value is only valid for ",
1054                                     super_scope,
1055                                     "");
1056                             }
1057                         }
1058                     }
1059                 }
1060
1061                 if let Some(_) = statement_scope_span(self.tcx, super_scope) {
1062                     db.note("consider using a `let` binding to increase its lifetime");
1063                 }
1064
1065
1066
1067                 match err.cmt.cat {
1068                     mc::Categorization::Rvalue(r, or) if r != or => {
1069                         db.note("\
1070 before rustc 1.16, this temporary lived longer - see issue #39283 \
1071 (https://github.com/rust-lang/rust/issues/39283)");
1072                     }
1073                     _ => {}
1074                 }
1075             }
1076
1077             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1078                 let descr = match opt_loan_path(&err.cmt) {
1079                     Some(lp) => {
1080                         format!("`{}`", self.loan_path_to_string(&lp))
1081                     }
1082                     None => self.cmt_to_string(&err.cmt),
1083                 };
1084                 self.tcx.note_and_explain_region(
1085                     db,
1086                     &format!("{} would have to be valid for ",
1087                             descr),
1088                     loan_scope,
1089                     "...");
1090                 self.tcx.note_and_explain_region(
1091                     db,
1092                     &format!("...but {} is only valid for ", descr),
1093                     ptr_scope,
1094                     "");
1095             }
1096         }
1097     }
1098
1099     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1100                                     error_span: &Span) {
1101         match err.cmt.note {
1102             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1103                 // If this is an `Fn` closure, it simply can't mutate upvars.
1104                 // If it's an `FnMut` closure, the original variable was declared immutable.
1105                 // We need to determine which is the case here.
1106                 let kind = match err.cmt.upvar().unwrap().cat {
1107                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1108                     _ => bug!()
1109                 };
1110                 if kind == ty::ClosureKind::Fn {
1111                     db.span_help(self.tcx.map.span(upvar_id.closure_expr_id),
1112                                  "consider changing this closure to take \
1113                                  self by mutable reference");
1114                 }
1115             }
1116             _ => {
1117                 if let Categorization::Deref(ref inner_cmt, ..) = err.cmt.cat {
1118                     if let Categorization::Local(local_id) = inner_cmt.cat {
1119                         let parent = self.tcx.map.get_parent_node(local_id);
1120
1121                         if let Some(fn_like) = FnLikeNode::from_node(self.tcx.map.get(parent)) {
1122                             if let Some(i) = self.tcx.map.body(fn_like.body()).arguments.iter()
1123                                                      .position(|arg| arg.pat.id == local_id) {
1124                                 let arg_ty = &fn_like.decl().inputs[i];
1125                                 if let hir::TyRptr(
1126                                     opt_lifetime,
1127                                     hir::MutTy{mutbl: hir::Mutability::MutImmutable, ref ty}) =
1128                                     arg_ty.node {
1129                                     if let Some(lifetime) = opt_lifetime {
1130                                         if let Ok(snippet) = self.tcx.sess.codemap()
1131                                             .span_to_snippet(ty.span) {
1132                                             if let Ok(lifetime_snippet) = self.tcx.sess.codemap()
1133                                                 .span_to_snippet(lifetime.span) {
1134                                                     db.span_label(arg_ty.span,
1135                                                                   &format!("use `&{} mut {}` \
1136                                                                             here to make mutable",
1137                                                                             lifetime_snippet,
1138                                                                             snippet));
1139                                             }
1140                                         }
1141                                     }
1142                                     else if let Ok(snippet) = self.tcx.sess.codemap()
1143                                         .span_to_snippet(arg_ty.span) {
1144                                         if snippet.starts_with("&") {
1145                                             db.span_label(arg_ty.span,
1146                                                           &format!("use `{}` here to make mutable",
1147                                                                    snippet.replace("&", "&mut ")));
1148                                         }
1149                                     }
1150                                 }
1151                             }
1152                         }
1153                     }
1154                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1155                     let span = self.tcx.map.span(local_id);
1156                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1157                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1158                             db.span_label(*error_span, &format!("cannot reborrow mutably"));
1159                             db.span_label(*error_span, &format!("try removing `&mut` here"));
1160                         } else {
1161                             if snippet.starts_with("ref ") {
1162                                 db.span_label(span, &format!("use `{}` here to make mutable",
1163                                                              snippet.replace("ref ", "ref mut ")));
1164                             } else if snippet != "self" {
1165                                 db.span_label(span,
1166                                               &format!("use `mut {}` here to make mutable",
1167                                                        snippet));
1168                             }
1169                             db.span_label(*error_span, &format!("cannot borrow mutably"));
1170                         }
1171                     } else {
1172                         db.span_label(*error_span, &format!("cannot borrow mutably"));
1173                     }
1174                 }
1175             }
1176         }
1177     }
1178     pub fn append_loan_path_to_string(&self,
1179                                       loan_path: &LoanPath<'tcx>,
1180                                       out: &mut String) {
1181         match loan_path.kind {
1182             LpUpvar(ty::UpvarId{ var_id: id, closure_expr_id: _ }) |
1183             LpVar(id) => {
1184                 out.push_str(&self.tcx.local_var_name_str(id));
1185             }
1186
1187             LpDowncast(ref lp_base, variant_def_id) => {
1188                 out.push('(');
1189                 self.append_loan_path_to_string(&lp_base, out);
1190                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1191                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1192                 out.push(')');
1193             }
1194
1195             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1196                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1197                 match fname {
1198                     mc::NamedField(fname) => {
1199                         out.push('.');
1200                         out.push_str(&fname.as_str());
1201                     }
1202                     mc::PositionalField(idx) => {
1203                         out.push('.');
1204                         out.push_str(&idx.to_string());
1205                     }
1206                 }
1207             }
1208
1209             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement(..))) => {
1210                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1211                 out.push_str("[..]");
1212             }
1213
1214             LpExtend(ref lp_base, _, LpDeref(_)) => {
1215                 out.push('*');
1216                 self.append_loan_path_to_string(&lp_base, out);
1217             }
1218         }
1219     }
1220
1221     pub fn append_autoderefd_loan_path_to_string(&self,
1222                                                  loan_path: &LoanPath<'tcx>,
1223                                                  out: &mut String) {
1224         match loan_path.kind {
1225             LpExtend(ref lp_base, _, LpDeref(_)) => {
1226                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1227                 // rules would normally allow users to omit the `*x`.
1228                 // So just serialize such paths to `x.f` or x[3]` respectively.
1229                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1230             }
1231
1232             LpDowncast(ref lp_base, variant_def_id) => {
1233                 out.push('(');
1234                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1235                 out.push(':');
1236                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1237                 out.push(')');
1238             }
1239
1240             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1241                 self.append_loan_path_to_string(loan_path, out)
1242             }
1243         }
1244     }
1245
1246     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1247         let mut result = String::new();
1248         self.append_loan_path_to_string(loan_path, &mut result);
1249         result
1250     }
1251
1252     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1253         cmt.descriptive_string(self.tcx)
1254     }
1255
1256     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1257         match opt_loan_path(cmt) {
1258             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1259             None => self.cmt_to_string(cmt),
1260         }
1261     }
1262 }
1263
1264 fn statement_scope_span(tcx: TyCtxt, region: &ty::Region) -> Option<Span> {
1265     match *region {
1266         ty::ReScope(scope) => {
1267             match tcx.map.find(scope.node_id(&tcx.region_maps)) {
1268                 Some(hir_map::NodeStmt(stmt)) => Some(stmt.span),
1269                 _ => None
1270             }
1271         }
1272         _ => None
1273     }
1274 }
1275
1276 impl BitwiseOperator for LoanDataFlowOperator {
1277     #[inline]
1278     fn join(&self, succ: usize, pred: usize) -> usize {
1279         succ | pred // loans from both preds are in scope
1280     }
1281 }
1282
1283 impl DataFlowOperator for LoanDataFlowOperator {
1284     #[inline]
1285     fn initial_value(&self) -> bool {
1286         false // no loans in scope by default
1287     }
1288 }
1289
1290 impl<'tcx> fmt::Debug for InteriorKind {
1291     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1292         match *self {
1293             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1294             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1295             InteriorElement(..) => write!(f, "[]"),
1296         }
1297     }
1298 }
1299
1300 impl<'tcx> fmt::Debug for Loan<'tcx> {
1301     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1302         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1303                self.index,
1304                self.loan_path,
1305                self.kind,
1306                self.gen_scope,
1307                self.kill_scope,
1308                self.restricted_paths)
1309     }
1310 }
1311
1312 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1313     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1314         match self.kind {
1315             LpVar(id) => {
1316                 write!(f, "$({})", ty::tls::with(|tcx| tcx.map.node_to_string(id)))
1317             }
1318
1319             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1320                 let s = ty::tls::with(|tcx| tcx.map.node_to_string(var_id));
1321                 write!(f, "$({} captured by id={})", s, closure_expr_id)
1322             }
1323
1324             LpDowncast(ref lp, variant_def_id) => {
1325                 let variant_str = if variant_def_id.is_local() {
1326                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1327                 } else {
1328                     format!("{:?}", variant_def_id)
1329                 };
1330                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1331             }
1332
1333             LpExtend(ref lp, _, LpDeref(_)) => {
1334                 write!(f, "{:?}.*", lp)
1335             }
1336
1337             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1338                 write!(f, "{:?}.{:?}", lp, interior)
1339             }
1340         }
1341     }
1342 }
1343
1344 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1345     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1346         match self.kind {
1347             LpVar(id) => {
1348                 write!(f, "$({})", ty::tls::with(|tcx| tcx.map.node_to_user_string(id)))
1349             }
1350
1351             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1352                 let s = ty::tls::with(|tcx| tcx.map.node_to_user_string(var_id));
1353                 write!(f, "$({} captured by closure)", s)
1354             }
1355
1356             LpDowncast(ref lp, variant_def_id) => {
1357                 let variant_str = if variant_def_id.is_local() {
1358                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1359                 } else {
1360                     format!("{:?}", variant_def_id)
1361                 };
1362                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1363             }
1364
1365             LpExtend(ref lp, _, LpDeref(_)) => {
1366                 write!(f, "{}.*", lp)
1367             }
1368
1369             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1370                 write!(f, "{}.{:?}", lp, interior)
1371             }
1372         }
1373     }
1374 }