src/librustc_borrowck/borrowck/mod.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! See The Book chapter on the borrow checker for more details.
  12
  13 #![allow(non_camel_case_types)]
  14
  15 pub use self::LoanPathKind::*;
  16 pub use self::LoanPathElem::*;
  17 pub use self::bckerr_code::*;
  18 pub use self::AliasableViolationKind::*;
  19 pub use self::MovedValueUseKind::*;
  20
  21 use self::InteriorKind::*;
  22
  23 use rustc::hir::map as hir_map;
  24 use rustc::hir::map::blocks::FnLikeNode;
  25 use rustc::cfg;
  26 use rustc::middle::dataflow::DataFlowContext;
  27 use rustc::middle::dataflow::BitwiseOperator;
  28 use rustc::middle::dataflow::DataFlowOperator;
  29 use rustc::middle::dataflow::KillFrom;
  30 use rustc::hir::def_id::{DefId, DefIndex};
  31 use rustc::middle::expr_use_visitor as euv;
  32 use rustc::middle::mem_categorization as mc;
  33 use rustc::middle::mem_categorization::Categorization;
  34 use rustc::middle::mem_categorization::ImmutabilityBlame;
  35 use rustc::middle::region::{self, RegionMaps};
  36 use rustc::middle::free_region::RegionRelations;
  37 use rustc::ty::{self, TyCtxt};
  38 use rustc::ty::maps::Providers;
  39 use rustc::util::nodemap::FxHashMap;
  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 #[derive(Clone, Copy)]
  57 pub struct LoanDataFlowOperator;
  58
  59 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  60
  61 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  62     for body_owner_def_id in tcx.body_owners() {
  63         tcx.borrowck(body_owner_def_id);
  64     }
  65 }
  66
  67 pub fn provide(providers: &mut Providers) {
  68     *providers = Providers {
  69         borrowck,
  70         ..*providers
  71     };
  72 }
  73
  74 /// Collection of conclusions determined via borrow checker analyses.
  75 pub struct AnalysisData<'a, 'tcx: 'a> {
  76     pub all_loans: Vec<Loan<'tcx>>,
  77     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  78     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  79 }
  80
  81 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId) {
  82     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  83
  84     let owner_id = tcx.hir.as_local_node_id(owner_def_id).unwrap();
  85
  86     match tcx.hir.get(owner_id) {
  87         hir_map::NodeStructCtor(_) |
  88         hir_map::NodeVariant(_) => {
  89             // We get invoked with anything that has MIR, but some of
  90             // those things (notably the synthesized constructors from
  91             // tuple structs/variants) do not have an associated body
  92             // and do not need borrowchecking.
  93             return;
  94         }
  95         _ => { }
  96     }
  97
  98     let body_id = tcx.hir.body_owned_by(owner_id);
  99     let tables = tcx.typeck_tables_of(owner_def_id);
 100     let region_maps = tcx.region_maps(owner_def_id);
 101     let body = tcx.hir.body(body_id);
 102     let bccx = &mut BorrowckCtxt { tcx, tables, region_maps, owner_def_id, body };
 103
 104     // Eventually, borrowck will always read the MIR, but at the
 105     // moment we do not. So, for now, we always force MIR to be
 106     // constructed for a given fn, since this may result in errors
 107     // being reported and we want that to happen.
 108     //
 109     // Note that `mir_validated` is a "stealable" result; the
 110     // thief, `optimized_mir()`, forces borrowck, so we know that
 111     // is not yet stolen.
 112     tcx.mir_validated(owner_def_id).borrow();
 113
 114     // option dance because you can't capture an uninitialized variable
 115     // by mut-ref.
 116     let mut cfg = None;
 117     if let Some(AnalysisData { all_loans,
 118                                loans: loan_dfcx,
 119                                move_data: flowed_moves }) =
 120         build_borrowck_dataflow_data(bccx, false, body_id,
 121                                      |bccx| {
 122                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 123                                          cfg.as_mut().unwrap()
 124                                      })
 125     {
 126         check_loans::check_loans(bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 127     }
 128 }
 129
 130 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 131                                                  force_analysis: bool,
 132                                                  body_id: hir::BodyId,
 133                                                  get_cfg: F)
 134                                                  -> Option<AnalysisData<'a, 'tcx>>
 135     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 136 {
 137     // Check the body of fn items.
 138     let tcx = this.tcx;
 139     let id_range = {
 140         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 141         visitor.visit_body(this.body);
 142         visitor.result()
 143     };
 144     let (all_loans, move_data) =
 145         gather_loans::gather_loans_in_fn(this, body_id);
 146
 147     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 148         // large arrays of data inserted as constants can take a lot of
 149         // time and memory to borrow-check - see issue #36799. However,
 150         // they don't have lvalues, so no borrow-check is actually needed.
 151         // Recognize that case and skip borrow-checking.
 152         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 153         return None;
 154     } else {
 155         debug!("propagating loans in {:?}", body_id);
 156     }
 157
 158     let cfg = get_cfg(this);
 159     let mut loan_dfcx =
 160         DataFlowContext::new(this.tcx,
 161                              "borrowck",
 162                              Some(this.body),
 163                              cfg,
 164                              LoanDataFlowOperator,
 165                              id_range,
 166                              all_loans.len());
 167     for (loan_idx, loan) in all_loans.iter().enumerate() {
 168         loan_dfcx.add_gen(loan.gen_scope.node_id(), loan_idx);
 169         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 170                            loan.kill_scope.node_id(), loan_idx);
 171     }
 172     loan_dfcx.add_kills_from_flow_exits(cfg);
 173     loan_dfcx.propagate(cfg, this.body);
 174
 175     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 176                                                       this,
 177                                                       cfg,
 178                                                       id_range,
 179                                                       this.body);
 180
 181     Some(AnalysisData { all_loans,
 182                         loans: loan_dfcx,
 183                         move_data:flowed_moves })
 184 }
 185
 186 /// Accessor for introspective clients inspecting `AnalysisData` and
 187 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 188 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 189     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 190     body_id: hir::BodyId,
 191     cfg: &cfg::CFG)
 192     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 193 {
 194     let owner_id = tcx.hir.body_owner(body_id);
 195     let owner_def_id = tcx.hir.local_def_id(owner_id);
 196     let tables = tcx.typeck_tables_of(owner_def_id);
 197     let region_maps = tcx.region_maps(owner_def_id);
 198     let body = tcx.hir.body(body_id);
 199     let mut bccx = BorrowckCtxt { tcx, tables, region_maps, owner_def_id, body };
 200
 201     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 202     (bccx, dataflow_data.unwrap())
 203 }
 204
 205 // ----------------------------------------------------------------------
 206 // Type definitions
 207
 208 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 209     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 210
 211     // tables for the current thing we are checking; set to
 212     // Some in `borrowck_fn` and cleared later
 213     tables: &'a ty::TypeckTables<'tcx>,
 214
 215     region_maps: Rc<RegionMaps>,
 216
 217     owner_def_id: DefId,
 218
 219     body: &'tcx hir::Body,
 220 }
 221
 222 ///////////////////////////////////////////////////////////////////////////
 223 // Loans and loan paths
 224
 225 /// Record of a loan that was issued.
 226 pub struct Loan<'tcx> {
 227     index: usize,
 228     loan_path: Rc<LoanPath<'tcx>>,
 229     kind: ty::BorrowKind,
 230     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 231
 232     /// gen_scope indicates where loan is introduced. Typically the
 233     /// loan is introduced at the point of the borrow, but in some
 234     /// cases, notably method arguments, the loan may be introduced
 235     /// only later, once it comes into scope.  See also
 236     /// `GatherLoanCtxt::compute_gen_scope`.
 237     gen_scope: region::CodeExtent,
 238
 239     /// kill_scope indicates when the loan goes out of scope.  This is
 240     /// either when the lifetime expires or when the local variable
 241     /// which roots the loan-path goes out of scope, whichever happens
 242     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 243     kill_scope: region::CodeExtent,
 244     span: Span,
 245     cause: euv::LoanCause,
 246 }
 247
 248 impl<'tcx> Loan<'tcx> {
 249     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 250         self.loan_path.clone()
 251     }
 252 }
 253
 254 #[derive(Eq)]
 255 pub struct LoanPath<'tcx> {
 256     kind: LoanPathKind<'tcx>,
 257     ty: ty::Ty<'tcx>,
 258 }
 259
 260 impl<'tcx> PartialEq for LoanPath<'tcx> {
 261     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 262         self.kind == that.kind
 263     }
 264 }
 265
 266 impl<'tcx> Hash for LoanPath<'tcx> {
 267     fn hash<H: Hasher>(&self, state: &mut H) {
 268         self.kind.hash(state);
 269     }
 270 }
 271
 272 #[derive(PartialEq, Eq, Hash, Debug)]
 273 pub enum LoanPathKind<'tcx> {
 274     LpVar(ast::NodeId),                         // `x` in README.md
 275     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 276     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 277     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 278 }
 279
 280 impl<'tcx> LoanPath<'tcx> {
 281     fn new(kind: LoanPathKind<'tcx>, ty: ty::Ty<'tcx>) -> LoanPath<'tcx> {
 282         LoanPath { kind: kind, ty: ty }
 283     }
 284
 285     fn to_type(&self) -> ty::Ty<'tcx> { self.ty }
 286 }
 287
 288 // FIXME (pnkfelix): See discussion here
 289 // https://github.com/pnkfelix/rust/commit/
 290 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 291 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 292
 293 // A local, "cleaned" version of `mc::InteriorKind` that drops
 294 // information that is not relevant to loan-path analysis. (In
 295 // particular, the distinction between how precisely an array-element
 296 // is tracked is irrelevant here.)
 297 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 298 pub enum InteriorKind {
 299     InteriorField(mc::FieldName),
 300     InteriorElement,
 301 }
 302
 303 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 304 impl ToInteriorKind for mc::InteriorKind {
 305     fn cleaned(self) -> InteriorKind {
 306         match self {
 307             mc::InteriorField(name) => InteriorField(name),
 308             mc::InteriorElement(_) => InteriorElement,
 309         }
 310     }
 311 }
 312
 313 // This can be:
 314 // - a pointer dereference (`*LV` in README.md)
 315 // - a field reference, with an optional definition of the containing
 316 //   enum variant (`LV.f` in README.md)
 317 // `DefId` is present when the field is part of struct that is in
 318 // a variant of an enum. For instance in:
 319 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 320 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 321 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 322 pub enum LoanPathElem<'tcx> {
 323     LpDeref(mc::PointerKind<'tcx>),
 324     LpInterior(Option<DefId>, InteriorKind),
 325 }
 326
 327 fn closure_to_block(closure_id: DefIndex,
 328                     tcx: TyCtxt) -> ast::NodeId {
 329     let closure_id = tcx.hir.def_index_to_node_id(closure_id);
 330     match tcx.hir.get(closure_id) {
 331         hir_map::NodeExpr(expr) => match expr.node {
 332             hir::ExprClosure(.., body_id, _, _) => {
 333                 body_id.node_id
 334             }
 335             _ => {
 336                 bug!("encountered non-closure id: {}", closure_id)
 337             }
 338         },
 339         _ => bug!("encountered non-expr id: {}", closure_id)
 340     }
 341 }
 342
 343 impl<'a, 'tcx> LoanPath<'tcx> {
 344     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::CodeExtent {
 345         match self.kind {
 346             LpVar(local_id) => bccx.region_maps.var_scope(local_id),
 347             LpUpvar(upvar_id) => {
 348                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 349                 region::CodeExtent::Misc(block_id)
 350             }
 351             LpDowncast(ref base, _) |
 352             LpExtend(ref base, ..) => base.kill_scope(bccx),
 353         }
 354     }
 355
 356     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 357         match (&self.kind, &other.kind) {
 358             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 359              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 360                 if id == id2 && opt_variant_id == opt_variant_id2 {
 361                     base.has_fork(&base2)
 362                 } else {
 363                     true
 364                 },
 365             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 366             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 367             _ => false,
 368         }
 369     }
 370
 371     fn depth(&self) -> usize {
 372         match self.kind {
 373             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 374             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 375             _ => 0,
 376         }
 377     }
 378
 379     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 380         match (&self.kind, &other.kind) {
 381             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 382              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 383                 if id == id2 && opt_variant_id == opt_variant_id2 {
 384                     base.common(&base2).map(|x| {
 385                         let xd = x.depth();
 386                         if base.depth() == xd && base2.depth() == xd {
 387                             LoanPath {
 388                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 389                                 ty: self.ty,
 390                             }
 391                         } else {
 392                             x
 393                         }
 394                     })
 395                 } else {
 396                     base.common(&base2)
 397                 }
 398             }
 399             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 400             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 401             (&LpVar(id), &LpVar(id2)) => {
 402                 if id == id2 {
 403                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 404                 } else {
 405                     None
 406                 }
 407             }
 408             (&LpUpvar(id), &LpUpvar(id2)) => {
 409                 if id == id2 {
 410                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 411                 } else {
 412                     None
 413                 }
 414             }
 415             _ => None,
 416         }
 417     }
 418 }
 419
 420 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 421     //! Computes the `LoanPath` (if any) for a `cmt`.
 422     //! Note that this logic is somewhat duplicated in
 423     //! the method `compute()` found in `gather_loans::restrictions`,
 424     //! which allows it to share common loan path pieces as it
 425     //! traverses the CMT.
 426
 427     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 428
 429     match cmt.cat {
 430         Categorization::Rvalue(..) |
 431         Categorization::StaticItem => {
 432             None
 433         }
 434
 435         Categorization::Local(id) => {
 436             Some(new_lp(LpVar(id)))
 437         }
 438
 439         Categorization::Upvar(mc::Upvar { id, .. }) => {
 440             Some(new_lp(LpUpvar(id)))
 441         }
 442
 443         Categorization::Deref(ref cmt_base, pk) => {
 444             opt_loan_path(cmt_base).map(|lp| {
 445                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 446             })
 447         }
 448
 449         Categorization::Interior(ref cmt_base, ik) => {
 450             opt_loan_path(cmt_base).map(|lp| {
 451                 let opt_variant_id = match cmt_base.cat {
 452                     Categorization::Downcast(_, did) =>  Some(did),
 453                     _ => None
 454                 };
 455                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 456             })
 457         }
 458
 459         Categorization::Downcast(ref cmt_base, variant_def_id) =>
 460             opt_loan_path(cmt_base)
 461             .map(|lp| {
 462                 new_lp(LpDowncast(lp, variant_def_id))
 463             }),
 464
 465     }
 466 }
 467
 468 ///////////////////////////////////////////////////////////////////////////
 469 // Errors
 470
 471 // Errors that can occur
 472 #[derive(Debug, PartialEq)]
 473 pub enum bckerr_code<'tcx> {
 474     err_mutbl,
 475     /// superscope, subscope, loan cause
 476     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 477     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 478 }
 479
 480 // Combination of an error code and the categorization of the expression
 481 // that caused it
 482 #[derive(Debug, PartialEq)]
 483 pub struct BckError<'tcx> {
 484     span: Span,
 485     cause: AliasableViolationKind,
 486     cmt: mc::cmt<'tcx>,
 487     code: bckerr_code<'tcx>
 488 }
 489
 490 #[derive(Copy, Clone, Debug, PartialEq)]
 491 pub enum AliasableViolationKind {
 492     MutabilityViolation,
 493     BorrowViolation(euv::LoanCause)
 494 }
 495
 496 #[derive(Copy, Clone, Debug)]
 497 pub enum MovedValueUseKind {
 498     MovedInUse,
 499     MovedInCapture,
 500 }
 501
 502 ///////////////////////////////////////////////////////////////////////////
 503 // Misc
 504
 505 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 506     pub fn is_subregion_of(&self,
 507                            r_sub: ty::Region<'tcx>,
 508                            r_sup: ty::Region<'tcx>)
 509                            -> bool
 510     {
 511         let region_rels = RegionRelations::new(self.tcx,
 512                                                self.owner_def_id,
 513                                                &self.region_maps,
 514                                                &self.tables.free_region_map);
 515         region_rels.is_subregion_of(r_sub, r_sup)
 516     }
 517
 518     pub fn report(&self, err: BckError<'tcx>) {
 519         // Catch and handle some particular cases.
 520         match (&err.code, &err.cause) {
 521             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 522              &BorrowViolation(euv::ClosureCapture(span))) |
 523             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 524              &BorrowViolation(euv::ClosureCapture(span))) |
 525             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 526              &BorrowViolation(euv::ClosureCapture(span))) => {
 527                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 528             }
 529             _ => { }
 530         }
 531
 532         self.report_bckerr(&err);
 533     }
 534
 535     pub fn report_use_of_moved_value(&self,
 536                                      use_span: Span,
 537                                      use_kind: MovedValueUseKind,
 538                                      lp: &LoanPath<'tcx>,
 539                                      the_move: &move_data::Move,
 540                                      moved_lp: &LoanPath<'tcx>,
 541                                      _param_env: ty::ParamEnv<'tcx>) {
 542         let (verb, verb_participle) = match use_kind {
 543             MovedInUse => ("use", "used"),
 544             MovedInCapture => ("capture", "captured"),
 545         };
 546
 547         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 548             move_data::Declared => {
 549                 // If this is an uninitialized variable, just emit a simple warning
 550                 // and return.
 551                 struct_span_err!(
 552                     self.tcx.sess, use_span, E0381,
 553                     "{} of possibly uninitialized variable: `{}`",
 554                     verb,
 555                     self.loan_path_to_string(lp))
 556                 .span_label(use_span, format!("use of possibly uninitialized `{}`",
 557                     self.loan_path_to_string(lp)))
 558                 .emit();
 559                 return;
 560             }
 561             _ => {
 562                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 563                 // normally generate a rather confusing message:
 564                 //
 565                 //     error: use of moved value: `x.b`
 566                 //     note: `x.a` moved here...
 567                 //
 568                 // What we want to do instead is get the 'common ancestor' of the two moves and
 569                 // use that for most of the message instead, giving is something like this:
 570                 //
 571                 //     error: use of moved value: `x`
 572                 //     note: `x` moved here (through moving `x.a`)...
 573
 574                 let common = moved_lp.common(lp);
 575                 let has_common = common.is_some();
 576                 let has_fork = moved_lp.has_fork(lp);
 577                 let (nl, ol, moved_lp_msg) =
 578                     if has_fork && has_common {
 579                         let nl = self.loan_path_to_string(&common.unwrap());
 580                         let ol = nl.clone();
 581                         let moved_lp_msg = format!(" (through moving `{}`)",
 582                                                    self.loan_path_to_string(moved_lp));
 583                         (nl, ol, moved_lp_msg)
 584                     } else {
 585                         (self.loan_path_to_string(lp),
 586                          self.loan_path_to_string(moved_lp),
 587                          String::new())
 588                     };
 589
 590                 let partial = moved_lp.depth() > lp.depth();
 591                 let msg = if !has_fork && partial { "partially " }
 592                           else if has_fork && !has_common { "collaterally "}
 593                           else { "" };
 594                 let mut err = struct_span_err!(
 595                     self.tcx.sess, use_span, E0382,
 596                     "{} of {}moved value: `{}`",
 597                     verb, msg, nl);
 598                 let need_note = match lp.ty.sty {
 599                     ty::TypeVariants::TyClosure(id, _) => {
 600                         let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
 601                         let hir_id = self.tcx.hir.node_to_hir_id(node_id);
 602                         if let Some(&(ty::ClosureKind::FnOnce, Some((span, name)))) =
 603                             self.tables.closure_kinds().get(hir_id)
 604                         {
 605                             err.span_note(span, &format!(
 606                                 "closure cannot be invoked more than once because \
 607                                 it moves the variable `{}` out of its environment",
 608                                 name
 609                             ));
 610                             false
 611                         } else {
 612                             true
 613                         }
 614                     }
 615                     _ => true,
 616                 };
 617                 (ol, moved_lp_msg, err, need_note)
 618             }
 619         };
 620
 621         // Get type of value and span where it was previously
 622         // moved.
 623         let (move_span, move_note) = match the_move.kind {
 624             move_data::Declared => {
 625                 unreachable!();
 626             }
 627
 628             move_data::MoveExpr |
 629             move_data::MovePat =>
 630                 (self.tcx.hir.span(the_move.id), ""),
 631
 632             move_data::Captured =>
 633                 (match self.tcx.hir.expect_expr(the_move.id).node {
 634                     hir::ExprClosure(.., fn_decl_span, _) => fn_decl_span,
 635                     ref r => bug!("Captured({}) maps to non-closure: {:?}",
 636                                   the_move.id, r),
 637                 }, " (into closure)"),
 638         };
 639
 640         // Annotate the use and the move in the span. Watch out for
 641         // the case where the use and the move are the same. This
 642         // means the use is in a loop.
 643         err = if use_span == move_span {
 644             err.span_label(
 645                 use_span,
 646                 format!("value moved{} here in previous iteration of loop",
 647                          move_note));
 648             err
 649         } else {
 650             err.span_label(use_span, format!("value {} here after move", verb_participle))
 651                .span_label(move_span, format!("value moved{} here", move_note));
 652             err
 653         };
 654
 655         if need_note {
 656             err.note(&format!("move occurs because `{}` has type `{}`, \
 657                                which does not implement the `Copy` trait",
 658                               self.loan_path_to_string(moved_lp),
 659                               moved_lp.ty));
 660         }
 661
 662         // Note: we used to suggest adding a `ref binding` or calling
 663         // `clone` but those suggestions have been removed because
 664         // they are often not what you actually want to do, and were
 665         // not considered particularly helpful.
 666
 667         err.emit();
 668     }
 669
 670     pub fn report_partial_reinitialization_of_uninitialized_structure(
 671             &self,
 672             span: Span,
 673             lp: &LoanPath<'tcx>) {
 674         span_err!(
 675             self.tcx.sess, span, E0383,
 676             "partial reinitialization of uninitialized structure `{}`",
 677             self.loan_path_to_string(lp));
 678     }
 679
 680     pub fn report_reassigned_immutable_variable(&self,
 681                                                 span: Span,
 682                                                 lp: &LoanPath<'tcx>,
 683                                                 assign:
 684                                                 &move_data::Assignment) {
 685         let mut err = struct_span_err!(
 686             self.tcx.sess, span, E0384,
 687             "re-assignment of immutable variable `{}`",
 688             self.loan_path_to_string(lp));
 689         err.span_label(span, "re-assignment of immutable variable");
 690         if span != assign.span {
 691             err.span_label(assign.span, format!("first assignment to `{}`",
 692                                               self.loan_path_to_string(lp)));
 693         }
 694         err.emit();
 695     }
 696
 697     pub fn span_err(&self, s: Span, m: &str) {
 698         self.tcx.sess.span_err(s, m);
 699     }
 700
 701     pub fn struct_span_err<S: Into<MultiSpan>>(&self, s: S, m: &str)
 702                                               -> DiagnosticBuilder<'a> {
 703         self.tcx.sess.struct_span_err(s, m)
 704     }
 705
 706     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 707                                                          s: S,
 708                                                          msg: &str,
 709                                                          code: &str)
 710                                                          -> DiagnosticBuilder<'a> {
 711         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 712     }
 713
 714     pub fn span_err_with_code<S: Into<MultiSpan>>(&self, s: S, msg: &str, code: &str) {
 715         self.tcx.sess.span_err_with_code(s, msg, code);
 716     }
 717
 718     fn report_bckerr(&self, err: &BckError<'tcx>) {
 719         let error_span = err.span.clone();
 720
 721         match err.code {
 722             err_mutbl => {
 723                 let descr = match err.cmt.note {
 724                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 725                         self.cmt_to_string(&err.cmt)
 726                     }
 727                     _ => match opt_loan_path(&err.cmt) {
 728                         None => {
 729                             format!("{} {}",
 730                                     err.cmt.mutbl.to_user_str(),
 731                                     self.cmt_to_string(&err.cmt))
 732
 733                         }
 734                         Some(lp) => {
 735                             format!("{} {} `{}`",
 736                                     err.cmt.mutbl.to_user_str(),
 737                                     self.cmt_to_string(&err.cmt),
 738                                     self.loan_path_to_string(&lp))
 739                         }
 740                     }
 741                 };
 742
 743                 let mut db = match err.cause {
 744                     MutabilityViolation => {
 745                         struct_span_err!(self.tcx.sess,
 746                                          error_span,
 747                                          E0594,
 748                                          "cannot assign to {}",
 749                                          descr)
 750                     }
 751                     BorrowViolation(euv::ClosureCapture(_)) => {
 752                         struct_span_err!(self.tcx.sess, error_span, E0595,
 753                                          "closure cannot assign to {}", descr)
 754                     }
 755                     BorrowViolation(euv::OverloadedOperator) |
 756                     BorrowViolation(euv::AddrOf) |
 757                     BorrowViolation(euv::RefBinding) |
 758                     BorrowViolation(euv::AutoRef) |
 759                     BorrowViolation(euv::AutoUnsafe) |
 760                     BorrowViolation(euv::ForLoop) |
 761                     BorrowViolation(euv::MatchDiscriminant) => {
 762                         struct_span_err!(self.tcx.sess, error_span, E0596,
 763                                          "cannot borrow {} as mutable", descr)
 764                     }
 765                     BorrowViolation(euv::ClosureInvocation) => {
 766                         span_bug!(err.span,
 767                             "err_mutbl with a closure invocation");
 768                     }
 769                 };
 770
 771                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 772                 self.note_immutability_blame(&mut db, err.cmt.immutability_blame());
 773                 db.emit();
 774             }
 775             err_out_of_scope(super_scope, sub_scope, cause) => {
 776                 let msg = match opt_loan_path(&err.cmt) {
 777                     None => "borrowed value".to_string(),
 778                     Some(lp) => {
 779                         format!("`{}`", self.loan_path_to_string(&lp))
 780                     }
 781                 };
 782
 783                 // When you have a borrow that lives across a yield,
 784                 // that reference winds up captured in the generator
 785                 // type. Regionck then constraints it to live as long
 786                 // as the generator itself. If that borrow is borrowing
 787                 // data owned by the generator, this winds up resulting in
 788                 // an `err_out_of_scope` error:
 789                 //
 790                 // ```
 791                 // {
 792                 //     let g = || {
 793                 //         let a = &3; // this borrow is forced to ... -+
 794                 //         yield ();          //                        |
 795                 //         println!("{}", a); //                        |
 796                 //     };                     //                        |
 797                 // } <----------------------... live until here --------+
 798                 // ```
 799                 //
 800                 // To detect this case, we look for cases where the
 801                 // `super_scope` (lifetime of the value) is within the
 802                 // body, but the `sub_scope` is not.
 803                 debug!("err_out_of_scope: self.body.is_generator = {:?}",
 804                        self.body.is_generator);
 805                 let maybe_borrow_across_yield = if self.body.is_generator {
 806                     let body_extent = region::CodeExtent::Misc(self.body.id().node_id);
 807                     debug!("err_out_of_scope: body_extent = {:?}", body_extent);
 808                     debug!("err_out_of_scope: super_scope = {:?}", super_scope);
 809                     debug!("err_out_of_scope: sub_scope = {:?}", sub_scope);
 810                     match (super_scope, sub_scope) {
 811                         (&ty::RegionKind::ReScope(value_extent),
 812                          &ty::RegionKind::ReScope(loan_extent)) => {
 813                             if {
 814                                 // value_extent <= body_extent &&
 815                                 self.region_maps.is_subscope_of(value_extent, body_extent) &&
 816                                     // body_extent <= loan_extent
 817                                     self.region_maps.is_subscope_of(body_extent, loan_extent)
 818                             } {
 819                                 // We now know that this is a case
 820                                 // that fits the bill described above:
 821                                 // a borrow of something whose scope
 822                                 // is within the generator, but the
 823                                 // borrow is for a scope outside the
 824                                 // generator.
 825                                 //
 826                                 // Now look within the scope of the of
 827                                 // the value being borrowed (in the
 828                                 // example above, that would be the
 829                                 // block remainder that starts with
 830                                 // `let a`) for a yield. We can cite
 831                                 // that for the user.
 832                                 self.tcx.yield_in_extent(value_extent, &mut FxHashMap())
 833                             } else {
 834                                 None
 835                             }
 836                         }
 837                         _ => None,
 838                     }
 839                 } else {
 840                     None
 841                 };
 842
 843                 if let Some(yield_span) = maybe_borrow_across_yield {
 844                     debug!("err_out_of_scope: opt_yield_span = {:?}", yield_span);
 845                     struct_span_err!(self.tcx.sess,
 846                                      error_span,
 847                                      E0626,
 848                                      "borrow may still be in use when generator yields")
 849                         .span_label(yield_span, "possible yield occurs here")
 850                         .emit();
 851                     return;
 852                 }
 853
 854                 let mut db = struct_span_err!(self.tcx.sess,
 855                                               error_span,
 856                                               E0597,
 857                                               "{} does not live long enough",
 858                                               msg);
 859
 860                 let (value_kind, value_msg) = match err.cmt.cat {
 861                     mc::Categorization::Rvalue(..) =>
 862                         ("temporary value", "temporary value created here"),
 863                     _ =>
 864                         ("borrowed value", "borrow occurs here")
 865                 };
 866
 867                 let is_closure = match cause {
 868                     euv::ClosureCapture(s) => {
 869                         // The primary span starts out as the closure creation point.
 870                         // Change the primary span here to highlight the use of the variable
 871                         // in the closure, because it seems more natural. Highlight
 872                         // closure creation point as a secondary span.
 873                         match db.span.primary_span() {
 874                             Some(primary) => {
 875                                 db.span = MultiSpan::from_span(s);
 876                                 db.span_label(primary, "capture occurs here");
 877                                 db.span_label(s, "does not live long enough");
 878                                 true
 879                             }
 880                             None => false
 881                         }
 882                     }
 883                     _ => {
 884                         db.span_label(error_span, "does not live long enough");
 885                         false
 886                     }
 887                 };
 888
 889                 let sub_span = self.region_end_span(sub_scope);
 890                 let super_span = self.region_end_span(super_scope);
 891
 892                 match (sub_span, super_span) {
 893                     (Some(s1), Some(s2)) if s1 == s2 => {
 894                         if !is_closure {
 895                             db.span = MultiSpan::from_span(s1);
 896                             db.span_label(error_span, value_msg);
 897                             let msg = match opt_loan_path(&err.cmt) {
 898                                 None => value_kind.to_string(),
 899                                 Some(lp) => {
 900                                     format!("`{}`", self.loan_path_to_string(&lp))
 901                                 }
 902                             };
 903                             db.span_label(s1,
 904                                           format!("{} dropped here while still borrowed", msg));
 905                         } else {
 906                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 907                         }
 908                         db.note("values in a scope are dropped in the opposite order \
 909                                 they are created");
 910                     }
 911                     (Some(s1), Some(s2)) if !is_closure => {
 912                         db.span = MultiSpan::from_span(s2);
 913                         db.span_label(error_span, value_msg);
 914                         let msg = match opt_loan_path(&err.cmt) {
 915                             None => value_kind.to_string(),
 916                             Some(lp) => {
 917                                 format!("`{}`", self.loan_path_to_string(&lp))
 918                             }
 919                         };
 920                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 921                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 922                     }
 923                     _ => {
 924                         match sub_span {
 925                             Some(s) => {
 926                                 db.span_label(s, format!("{} needs to live until here",
 927                                                           value_kind));
 928                             }
 929                             None => {
 930                                 self.tcx.note_and_explain_region(
 931                                     &mut db,
 932                                     "borrowed value must be valid for ",
 933                                     sub_scope,
 934                                     "...");
 935                             }
 936                         }
 937                         match super_span {
 938                             Some(s) => {
 939                                 db.span_label(s, format!("{} only lives until here", value_kind));
 940                             }
 941                             None => {
 942                                 self.tcx.note_and_explain_region(
 943                                     &mut db,
 944                                     "...but borrowed value is only valid for ",
 945                                     super_scope,
 946                                     "");
 947                             }
 948                         }
 949                     }
 950                 }
 951
 952                 if let Some(_) = statement_scope_span(self.tcx, super_scope) {
 953                     db.note("consider using a `let` binding to increase its lifetime");
 954                 }
 955
 956                 db.emit();
 957             }
 958             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
 959                 let descr = self.cmt_to_path_or_string(&err.cmt);
 960                 let mut db = struct_span_err!(self.tcx.sess, error_span, E0598,
 961                                               "lifetime of {} is too short to guarantee \
 962                                                its contents can be safely reborrowed",
 963                                               descr);
 964
 965                 let descr = match opt_loan_path(&err.cmt) {
 966                     Some(lp) => {
 967                         format!("`{}`", self.loan_path_to_string(&lp))
 968                     }
 969                     None => self.cmt_to_string(&err.cmt),
 970                 };
 971                 self.tcx.note_and_explain_region(
 972                     &mut db,
 973                     &format!("{} would have to be valid for ",
 974                             descr),
 975                     loan_scope,
 976                     "...");
 977                 self.tcx.note_and_explain_region(
 978                     &mut db,
 979                     &format!("...but {} is only valid for ", descr),
 980                     ptr_scope,
 981                     "");
 982
 983                 db.emit();
 984             }
 985         }
 986     }
 987
 988     pub fn report_aliasability_violation(&self,
 989                                          span: Span,
 990                                          kind: AliasableViolationKind,
 991                                          cause: mc::AliasableReason,
 992                                          cmt: mc::cmt<'tcx>) {
 993         let mut is_closure = false;
 994         let prefix = match kind {
 995             MutabilityViolation => {
 996                 "cannot assign to data"
 997             }
 998             BorrowViolation(euv::ClosureCapture(_)) |
 999             BorrowViolation(euv::OverloadedOperator) |
1000             BorrowViolation(euv::AddrOf) |
1001             BorrowViolation(euv::AutoRef) |
1002             BorrowViolation(euv::AutoUnsafe) |
1003             BorrowViolation(euv::RefBinding) |
1004             BorrowViolation(euv::MatchDiscriminant) => {
1005                 "cannot borrow data mutably"
1006             }
1007
1008             BorrowViolation(euv::ClosureInvocation) => {
1009                 is_closure = true;
1010                 "closure invocation"
1011             }
1012
1013             BorrowViolation(euv::ForLoop) => {
1014                 "`for` loop"
1015             }
1016         };
1017
1018         match cause {
1019             mc::AliasableStatic |
1020             mc::AliasableStaticMut => {
1021                 // This path cannot occur. It happens when we have an
1022                 // `&mut` or assignment to a static. But in the case
1023                 // of `static X`, we get a mutability violation first,
1024                 // and never get here. In the case of `static mut X`,
1025                 // that is unsafe and hence the aliasability error is
1026                 // ignored.
1027                 span_bug!(span, "aliasability violation for static `{}`", prefix)
1028             }
1029             mc::AliasableBorrowed => {}
1030         };
1031         let blame = cmt.immutability_blame();
1032         let mut err = match blame {
1033             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1034                 let mut err = struct_span_err!(
1035                     self.tcx.sess, span, E0387,
1036                     "{} in a captured outer variable in an `Fn` closure", prefix);
1037
1038                 // FIXME: the distinction between these 2 messages looks wrong.
1039                 let help = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1040                     // The aliasability violation with closure captures can
1041                     // happen for nested closures, so we know the enclosing
1042                     // closure incorrectly accepts an `Fn` while it needs to
1043                     // be `FnMut`.
1044                     "consider changing this to accept closures that implement `FnMut`"
1045
1046                 } else {
1047                     "consider changing this closure to take self by mutable reference"
1048                 };
1049                 let node_id = self.tcx.hir.def_index_to_node_id(id);
1050                 err.span_help(self.tcx.hir.span(node_id), help);
1051                 err
1052             }
1053             _ =>  {
1054                 let mut err = struct_span_err!(
1055                     self.tcx.sess, span, E0389,
1056                     "{} in a `&` reference", prefix);
1057                 err.span_label(span, "assignment into an immutable reference");
1058                 err
1059             }
1060         };
1061         self.note_immutability_blame(&mut err, blame);
1062
1063         if is_closure {
1064             err.help("closures behind references must be called via `&mut`");
1065         }
1066         err.emit();
1067     }
1068
1069     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1070     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1071         // Check wether the argument is an immutable reference
1072         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1073         if let hir::TyRptr(lifetime, hir::MutTy {
1074             mutbl: hir::Mutability::MutImmutable,
1075             ref ty
1076         }) = pty.node {
1077             // Account for existing lifetimes when generating the message
1078             let pointee_snippet = match self.tcx.sess.codemap().span_to_snippet(ty.span) {
1079                 Ok(snippet) => snippet,
1080                 _ => return None
1081             };
1082
1083             let lifetime_snippet = if !lifetime.is_elided() {
1084                 format!("{} ", match self.tcx.sess.codemap().span_to_snippet(lifetime.span) {
1085                     Ok(lifetime_snippet) => lifetime_snippet,
1086                     _ => return None
1087                 })
1088             } else {
1089                 String::new()
1090             };
1091             Some(format!("use `&{}mut {}` here to make mutable",
1092                          lifetime_snippet,
1093                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1094         } else {
1095             None
1096         }
1097     }
1098
1099     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1100         let pat = match self.tcx.hir.get(node_id) {
1101             hir_map::Node::NodeLocal(pat) => pat,
1102             node => bug!("bad node for local: {:?}", node)
1103         };
1104
1105         match pat.node {
1106             hir::PatKind::Binding(..) => {
1107                 *self.tables
1108                      .pat_binding_modes()
1109                      .get(pat.hir_id)
1110                      .expect("missing binding mode")
1111             }
1112             _ => bug!("local is not a binding: {:?}", pat)
1113         }
1114     }
1115
1116     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1117         let parent = self.tcx.hir.get_parent_node(node_id);
1118         let parent_node = self.tcx.hir.get(parent);
1119
1120         // The parent node is like a fn
1121         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1122             // `nid`'s parent's `Body`
1123             let fn_body = self.tcx.hir.body(fn_like.body());
1124             // Get the position of `node_id` in the arguments list
1125             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1126             if let Some(i) = arg_pos {
1127                 // The argument's `Ty`
1128                 (Some(&fn_like.decl().inputs[i]),
1129                  i == 0 && fn_like.decl().has_implicit_self)
1130             } else {
1131                 (None, false)
1132             }
1133         } else {
1134             (None, false)
1135         }
1136     }
1137
1138     fn note_immutability_blame(&self,
1139                                db: &mut DiagnosticBuilder,
1140                                blame: Option<ImmutabilityBlame>) {
1141         match blame {
1142             None => {}
1143             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1144             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1145                 let let_span = self.tcx.hir.span(node_id);
1146                 if let ty::BindByValue(..) = self.local_binding_mode(node_id) {
1147                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(let_span) {
1148                         let (_, is_implicit_self) = self.local_ty(node_id);
1149                         if is_implicit_self && snippet != "self" {
1150                             // avoid suggesting `mut &self`.
1151                             return
1152                         }
1153                         db.span_label(
1154                             let_span,
1155                             format!("consider changing this to `mut {}`", snippet)
1156                         );
1157                     }
1158                 }
1159             }
1160             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1161                 let let_span = self.tcx.hir.span(node_id);
1162                 match self.local_binding_mode(node_id) {
1163                     ty::BindByReference(..) => {
1164                         let snippet = self.tcx.sess.codemap().span_to_snippet(let_span);
1165                         if let Ok(snippet) = snippet {
1166                             db.span_label(
1167                                 let_span,
1168                                 format!("consider changing this to `{}`",
1169                                          snippet.replace("ref ", "ref mut "))
1170                             );
1171                         }
1172                     }
1173                     ty::BindByValue(..) => {
1174                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1175                             if let Some(msg) =
1176                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1177                                 db.span_label(local_ty.span, msg);
1178                             }
1179                         }
1180                     }
1181                 }
1182             }
1183             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1184                 let node_id = match self.tcx.hir.as_local_node_id(field.did) {
1185                     Some(node_id) => node_id,
1186                     None => return
1187                 };
1188
1189                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(node_id) {
1190                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1191                         db.span_label(field.ty.span, msg);
1192                     }
1193                 }
1194             }
1195         }
1196     }
1197
1198     fn report_out_of_scope_escaping_closure_capture(&self,
1199                                                     err: &BckError<'tcx>,
1200                                                     capture_span: Span)
1201     {
1202         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1203
1204         let suggestion =
1205             match self.tcx.sess.codemap().span_to_snippet(err.span) {
1206                 Ok(string) => format!("move {}", string),
1207                 Err(_) => format!("move |<args>| <body>")
1208             };
1209
1210         struct_span_err!(self.tcx.sess, err.span, E0373,
1211                          "closure may outlive the current function, \
1212                           but it borrows {}, \
1213                           which is owned by the current function",
1214                          cmt_path_or_string)
1215             .span_label(capture_span,
1216                        format!("{} is borrowed here",
1217                                 cmt_path_or_string))
1218             .span_label(err.span,
1219                        format!("may outlive borrowed value {}",
1220                                 cmt_path_or_string))
1221             .span_suggestion(err.span,
1222                              &format!("to force the closure to take ownership of {} \
1223                                        (and any other referenced variables), \
1224                                        use the `move` keyword",
1225                                        cmt_path_or_string),
1226                              suggestion)
1227             .emit();
1228     }
1229
1230     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1231         match *region {
1232             ty::ReScope(scope) => {
1233                 match scope.span(&self.tcx.hir) {
1234                     Some(s) => {
1235                         Some(s.end_point())
1236                     }
1237                     None => {
1238                         None
1239                     }
1240                 }
1241             }
1242             _ => None
1243         }
1244     }
1245
1246     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1247                                     error_span: &Span) {
1248         match err.cmt.note {
1249             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1250                 // If this is an `Fn` closure, it simply can't mutate upvars.
1251                 // If it's an `FnMut` closure, the original variable was declared immutable.
1252                 // We need to determine which is the case here.
1253                 let kind = match err.cmt.upvar().unwrap().cat {
1254                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1255                     _ => bug!()
1256                 };
1257                 if kind == ty::ClosureKind::Fn {
1258                     let closure_node_id =
1259                         self.tcx.hir.def_index_to_node_id(upvar_id.closure_expr_id);
1260                     db.span_help(self.tcx.hir.span(closure_node_id),
1261                                  "consider changing this closure to take \
1262                                   self by mutable reference");
1263                 }
1264             }
1265             _ => {
1266                 if let Categorization::Deref(..) = err.cmt.cat {
1267                     db.span_label(*error_span, "cannot borrow as mutable");
1268                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1269                     let span = self.tcx.hir.span(local_id);
1270                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1271                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1272                             db.span_label(*error_span, "cannot reborrow mutably");
1273                             db.span_label(*error_span, "try removing `&mut` here");
1274                         } else {
1275                             db.span_label(*error_span, "cannot borrow mutably");
1276                         }
1277                     } else {
1278                         db.span_label(*error_span, "cannot borrow mutably");
1279                     }
1280                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1281                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1282                         db.span_label(*error_span,
1283                                       "cannot mutably borrow immutable field");
1284                     }
1285                 }
1286             }
1287         }
1288     }
1289     pub fn append_loan_path_to_string(&self,
1290                                       loan_path: &LoanPath<'tcx>,
1291                                       out: &mut String) {
1292         match loan_path.kind {
1293             LpUpvar(ty::UpvarId { var_id: id, closure_expr_id: _ }) => {
1294                 out.push_str(&self.tcx.local_var_name_str_def_index(id));
1295             }
1296             LpVar(id) => {
1297                 out.push_str(&self.tcx.local_var_name_str(id));
1298             }
1299
1300             LpDowncast(ref lp_base, variant_def_id) => {
1301                 out.push('(');
1302                 self.append_loan_path_to_string(&lp_base, out);
1303                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1304                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1305                 out.push(')');
1306             }
1307
1308             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1309                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1310                 match fname {
1311                     mc::NamedField(fname) => {
1312                         out.push('.');
1313                         out.push_str(&fname.as_str());
1314                     }
1315                     mc::PositionalField(idx) => {
1316                         out.push('.');
1317                         out.push_str(&idx.to_string());
1318                     }
1319                 }
1320             }
1321
1322             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1323                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1324                 out.push_str("[..]");
1325             }
1326
1327             LpExtend(ref lp_base, _, LpDeref(_)) => {
1328                 out.push('*');
1329                 self.append_loan_path_to_string(&lp_base, out);
1330             }
1331         }
1332     }
1333
1334     pub fn append_autoderefd_loan_path_to_string(&self,
1335                                                  loan_path: &LoanPath<'tcx>,
1336                                                  out: &mut String) {
1337         match loan_path.kind {
1338             LpExtend(ref lp_base, _, LpDeref(_)) => {
1339                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1340                 // rules would normally allow users to omit the `*x`.
1341                 // So just serialize such paths to `x.f` or x[3]` respectively.
1342                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1343             }
1344
1345             LpDowncast(ref lp_base, variant_def_id) => {
1346                 out.push('(');
1347                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1348                 out.push(':');
1349                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1350                 out.push(')');
1351             }
1352
1353             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1354                 self.append_loan_path_to_string(loan_path, out)
1355             }
1356         }
1357     }
1358
1359     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1360         let mut result = String::new();
1361         self.append_loan_path_to_string(loan_path, &mut result);
1362         result
1363     }
1364
1365     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1366         cmt.descriptive_string(self.tcx)
1367     }
1368
1369     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1370         match opt_loan_path(cmt) {
1371             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1372             None => self.cmt_to_string(cmt),
1373         }
1374     }
1375 }
1376
1377 fn statement_scope_span(tcx: TyCtxt, region: ty::Region) -> Option<Span> {
1378     match *region {
1379         ty::ReScope(scope) => {
1380             match tcx.hir.find(scope.node_id()) {
1381                 Some(hir_map::NodeStmt(stmt)) => Some(stmt.span),
1382                 _ => None
1383             }
1384         }
1385         _ => None
1386     }
1387 }
1388
1389 impl BitwiseOperator for LoanDataFlowOperator {
1390     #[inline]
1391     fn join(&self, succ: usize, pred: usize) -> usize {
1392         succ | pred // loans from both preds are in scope
1393     }
1394 }
1395
1396 impl DataFlowOperator for LoanDataFlowOperator {
1397     #[inline]
1398     fn initial_value(&self) -> bool {
1399         false // no loans in scope by default
1400     }
1401 }
1402
1403 impl<'tcx> fmt::Debug for InteriorKind {
1404     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1405         match *self {
1406             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1407             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1408             InteriorElement => write!(f, "[]"),
1409         }
1410     }
1411 }
1412
1413 impl<'tcx> fmt::Debug for Loan<'tcx> {
1414     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1415         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1416                self.index,
1417                self.loan_path,
1418                self.kind,
1419                self.gen_scope,
1420                self.kill_scope,
1421                self.restricted_paths)
1422     }
1423 }
1424
1425 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1426     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1427         match self.kind {
1428             LpVar(id) => {
1429                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1430             }
1431
1432             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1433                 let s = ty::tls::with(|tcx| {
1434                     let var_node_id = tcx.hir.def_index_to_node_id(var_id);
1435                     tcx.hir.node_to_string(var_node_id)
1436                 });
1437                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1438             }
1439
1440             LpDowncast(ref lp, variant_def_id) => {
1441                 let variant_str = if variant_def_id.is_local() {
1442                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1443                 } else {
1444                     format!("{:?}", variant_def_id)
1445                 };
1446                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1447             }
1448
1449             LpExtend(ref lp, _, LpDeref(_)) => {
1450                 write!(f, "{:?}.*", lp)
1451             }
1452
1453             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1454                 write!(f, "{:?}.{:?}", lp, interior)
1455             }
1456         }
1457     }
1458 }
1459
1460 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1461     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1462         match self.kind {
1463             LpVar(id) => {
1464                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1465             }
1466
1467             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1468                 let s = ty::tls::with(|tcx| {
1469                     let var_node_id = tcx.hir.def_index_to_node_id(var_id);
1470                     tcx.hir.node_to_string(var_node_id)
1471                 });
1472                 write!(f, "$({} captured by closure)", s)
1473             }
1474
1475             LpDowncast(ref lp, variant_def_id) => {
1476                 let variant_str = if variant_def_id.is_local() {
1477                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1478                 } else {
1479                     format!("{:?}", variant_def_id)
1480                 };
1481                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1482             }
1483
1484             LpExtend(ref lp, _, LpDeref(_)) => {
1485                 write!(f, "{}.*", lp)
1486             }
1487
1488             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1489                 write!(f, "{}.{:?}", lp, interior)
1490             }
1491         }
1492     }
1493 }