src/librustc_borrowck/borrowck/mod.rs

   1 //! See The Book chapter on the borrow checker for more details.
   2
   3 #![allow(non_camel_case_types)]
   4
   5 pub use LoanPathKind::*;
   6 pub use LoanPathElem::*;
   7 pub use bckerr_code::*;
   8 pub use AliasableViolationKind::*;
   9 pub use MovedValueUseKind::*;
  10
  11 use InteriorKind::*;
  12
  13 use rustc::hir::HirId;
  14 use rustc::hir::Node;
  15 use rustc::hir::map::blocks::FnLikeNode;
  16 use rustc::cfg;
  17 use rustc::middle::borrowck::{BorrowCheckResult, SignalledError};
  18 use rustc::hir::def_id::{DefId, LocalDefId};
  19 use rustc::middle::expr_use_visitor as euv;
  20 use rustc::middle::mem_categorization as mc;
  21 use rustc::middle::mem_categorization::Categorization;
  22 use rustc::middle::mem_categorization::ImmutabilityBlame;
  23 use rustc::middle::region;
  24 use rustc::middle::free_region::RegionRelations;
  25 use rustc::ty::{self, Ty, TyCtxt};
  26 use rustc::ty::query::Providers;
  27 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  28 use rustc_mir::util::suggest_ref_mut;
  29 use rustc::util::nodemap::FxHashSet;
  30
  31 use std::borrow::Cow;
  32 use std::cell::{Cell, RefCell};
  33 use std::fmt;
  34 use std::rc::Rc;
  35 use std::hash::{Hash, Hasher};
  36 use syntax::source_map::CompilerDesugaringKind;
  37 use syntax_pos::{MultiSpan, Span};
  38 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
  39 use log::debug;
  40
  41 use rustc::hir;
  42
  43 use crate::dataflow::{DataFlowContext, BitwiseOperator, DataFlowOperator, KillFrom};
  44
  45 pub mod check_loans;
  46
  47 pub mod gather_loans;
  48
  49 pub mod move_data;
  50
  51 #[derive(Clone, Copy)]
  52 pub struct LoanDataFlowOperator;
  53
  54 pub type LoanDataFlow<'tcx> = DataFlowContext<'tcx, LoanDataFlowOperator>;
  55
  56 pub fn check_crate<'tcx>(tcx: TyCtxt<'tcx, 'tcx>) {
  57     tcx.par_body_owners(|body_owner_def_id| {
  58         tcx.ensure().borrowck(body_owner_def_id);
  59     });
  60 }
  61
  62 pub fn provide(providers: &mut Providers<'_>) {
  63     *providers = Providers {
  64         borrowck,
  65         ..*providers
  66     };
  67 }
  68
  69 /// Collection of conclusions determined via borrow checker analyses.
  70 pub struct AnalysisData<'tcx> {
  71     pub all_loans: Vec<Loan<'tcx>>,
  72     pub loans: DataFlowContext<'tcx, LoanDataFlowOperator>,
  73     pub move_data: move_data::FlowedMoveData<'tcx>,
  74 }
  75
  76 fn borrowck<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, owner_def_id: DefId) -> &'tcx BorrowCheckResult {
  77     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  78
  79     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  80
  81     let owner_id = tcx.hir().as_local_hir_id(owner_def_id).unwrap();
  82
  83     match tcx.hir().get_by_hir_id(owner_id) {
  84         Node::Ctor(..) => {
  85             // We get invoked with anything that has MIR, but some of
  86             // those things (notably the synthesized constructors from
  87             // tuple structs/variants) do not have an associated body
  88             // and do not need borrowchecking.
  89             return tcx.arena.alloc(BorrowCheckResult {
  90                 used_mut_nodes: Default::default(),
  91                 signalled_any_error: SignalledError::NoErrorsSeen,
  92             })
  93         }
  94         _ => { }
  95     }
  96
  97     let body_id = tcx.hir().body_owned_by(owner_id);
  98     let tables = tcx.typeck_tables_of(owner_def_id);
  99     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 100     let body = tcx.hir().body(body_id);
 101     let mut bccx = BorrowckCtxt {
 102         tcx,
 103         tables,
 104         region_scope_tree,
 105         owner_def_id,
 106         body,
 107         used_mut_nodes: Default::default(),
 108         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 109     };
 110
 111     // Eventually, borrowck will always read the MIR, but at the
 112     // moment we do not. So, for now, we always force MIR to be
 113     // constructed for a given fn, since this may result in errors
 114     // being reported and we want that to happen.
 115     //
 116     // Note that `mir_validated` is a "stealable" result; the
 117     // thief, `optimized_mir()`, forces borrowck, so we know that
 118     // is not yet stolen.
 119     tcx.ensure().mir_validated(owner_def_id);
 120
 121     // option dance because you can't capture an uninitialized variable
 122     // by mut-ref.
 123     let mut cfg = None;
 124     if let Some(AnalysisData { all_loans,
 125                                loans: loan_dfcx,
 126                                move_data: flowed_moves }) =
 127         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 128                                      |bccx| {
 129                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 130                                          cfg.as_mut().unwrap()
 131                                      })
 132     {
 133         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 134     }
 135
 136     tcx.arena.alloc(BorrowCheckResult {
 137         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 138         signalled_any_error: bccx.signalled_any_error.into_inner(),
 139     })
 140 }
 141
 142 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(
 143     this: &mut BorrowckCtxt<'a, 'tcx>,
 144     force_analysis: bool,
 145     body_id: hir::BodyId,
 146     get_cfg: F,
 147 ) -> Option<AnalysisData<'tcx>>
 148 where
 149     F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG,
 150 {
 151     // Check the body of fn items.
 152     let (all_loans, move_data) =
 153         gather_loans::gather_loans_in_fn(this, body_id);
 154
 155     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 156         // large arrays of data inserted as constants can take a lot of
 157         // time and memory to borrow-check - see issue #36799. However,
 158         // they don't have places, so no borrow-check is actually needed.
 159         // Recognize that case and skip borrow-checking.
 160         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 161         return None;
 162     } else {
 163         debug!("propagating loans in {:?}", body_id);
 164     }
 165
 166     let cfg = get_cfg(this);
 167     let mut loan_dfcx =
 168         DataFlowContext::new(this.tcx,
 169                              "borrowck",
 170                              Some(this.body),
 171                              cfg,
 172                              LoanDataFlowOperator,
 173                              all_loans.len());
 174     for (loan_idx, loan) in all_loans.iter().enumerate() {
 175         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 176         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 177                            loan.kill_scope.item_local_id(),
 178                            loan_idx);
 179     }
 180     loan_dfcx.add_kills_from_flow_exits(cfg);
 181     loan_dfcx.propagate(cfg, this.body);
 182
 183     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 184                                                       this,
 185                                                       cfg,
 186                                                       this.body);
 187
 188     Some(AnalysisData { all_loans,
 189                         loans: loan_dfcx,
 190                         move_data:flowed_moves })
 191 }
 192
 193 /// Accessor for introspective clients inspecting `AnalysisData` and
 194 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 195 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 196     tcx: TyCtxt<'tcx, 'tcx>,
 197     body_id: hir::BodyId,
 198     cfg: &cfg::CFG,
 199 ) -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'tcx>) {
 200     let owner_id = tcx.hir().body_owner(body_id);
 201     let owner_def_id = tcx.hir().local_def_id(owner_id);
 202     let tables = tcx.typeck_tables_of(owner_def_id);
 203     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 204     let body = tcx.hir().body(body_id);
 205     let mut bccx = BorrowckCtxt {
 206         tcx,
 207         tables,
 208         region_scope_tree,
 209         owner_def_id,
 210         body,
 211         used_mut_nodes: Default::default(),
 212         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 213     };
 214
 215     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 216     (bccx, dataflow_data.unwrap())
 217 }
 218
 219 // ----------------------------------------------------------------------
 220 // Type definitions
 221
 222 pub struct BorrowckCtxt<'a, 'tcx> {
 223     tcx: TyCtxt<'tcx, 'tcx>,
 224
 225     // tables for the current thing we are checking; set to
 226     // Some in `borrowck_fn` and cleared later
 227     tables: &'a ty::TypeckTables<'tcx>,
 228
 229     region_scope_tree: &'tcx region::ScopeTree,
 230
 231     owner_def_id: DefId,
 232
 233     body: &'tcx hir::Body,
 234
 235     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 236
 237     signalled_any_error: Cell<SignalledError>,
 238 }
 239
 240 impl BorrowckCtxt<'_, 'tcx> {
 241     fn signal_error(&self) {
 242         self.signalled_any_error.set(SignalledError::SawSomeError);
 243     }
 244 }
 245
 246 impl BorrowckErrors<'a> for &'a BorrowckCtxt<'_, 'tcx> {
 247     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 248                                                      sp: S,
 249                                                      msg: &str,
 250                                                      code: DiagnosticId)
 251                                                      -> DiagnosticBuilder<'a>
 252     {
 253         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 254     }
 255
 256     fn struct_span_err<S: Into<MultiSpan>>(self,
 257                                            sp: S,
 258                                            msg: &str)
 259                                            -> DiagnosticBuilder<'a>
 260     {
 261         self.tcx.sess.struct_span_err(sp, msg)
 262     }
 263
 264     fn cancel_if_wrong_origin(self,
 265                               mut diag: DiagnosticBuilder<'a>,
 266                               o: Origin)
 267                               -> DiagnosticBuilder<'a>
 268     {
 269         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 270             self.tcx.sess.diagnostic().cancel(&mut diag);
 271         }
 272         diag
 273     }
 274 }
 275
 276 ///////////////////////////////////////////////////////////////////////////
 277 // Loans and loan paths
 278
 279 /// Record of a loan that was issued.
 280 pub struct Loan<'tcx> {
 281     index: usize,
 282     loan_path: Rc<LoanPath<'tcx>>,
 283     kind: ty::BorrowKind,
 284     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 285
 286     /// gen_scope indicates where loan is introduced. Typically the
 287     /// loan is introduced at the point of the borrow, but in some
 288     /// cases, notably method arguments, the loan may be introduced
 289     /// only later, once it comes into scope. See also
 290     /// `GatherLoanCtxt::compute_gen_scope`.
 291     gen_scope: region::Scope,
 292
 293     /// kill_scope indicates when the loan goes out of scope. This is
 294     /// either when the lifetime expires or when the local variable
 295     /// which roots the loan-path goes out of scope, whichever happens
 296     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 297     kill_scope: region::Scope,
 298     span: Span,
 299     cause: euv::LoanCause,
 300 }
 301
 302 impl<'tcx> Loan<'tcx> {
 303     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 304         self.loan_path.clone()
 305     }
 306 }
 307
 308 #[derive(Eq)]
 309 pub struct LoanPath<'tcx> {
 310     kind: LoanPathKind<'tcx>,
 311     ty: Ty<'tcx>,
 312 }
 313
 314 impl<'tcx> PartialEq for LoanPath<'tcx> {
 315     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 316         self.kind == that.kind
 317     }
 318 }
 319
 320 impl<'tcx> Hash for LoanPath<'tcx> {
 321     fn hash<H: Hasher>(&self, state: &mut H) {
 322         self.kind.hash(state);
 323     }
 324 }
 325
 326 #[derive(PartialEq, Eq, Hash, Debug)]
 327 pub enum LoanPathKind<'tcx> {
 328     LpVar(hir::HirId),                          // `x` in README.md
 329     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 330     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 331     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 332 }
 333
 334 impl<'tcx> LoanPath<'tcx> {
 335     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 336         LoanPath { kind: kind, ty: ty }
 337     }
 338
 339     fn to_type(&self) -> Ty<'tcx> { self.ty }
 340
 341     fn has_downcast(&self) -> bool {
 342         match self.kind {
 343             LpDowncast(_, _) => true,
 344             LpExtend(ref lp, _, LpInterior(_, _)) => {
 345                 lp.has_downcast()
 346             }
 347             _ => false,
 348         }
 349     }
 350 }
 351
 352 // FIXME (pnkfelix): See discussion here
 353 // https://github.com/pnkfelix/rust/commit/
 354 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 355 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 356
 357 // A local, "cleaned" version of `mc::InteriorKind` that drops
 358 // information that is not relevant to loan-path analysis. (In
 359 // particular, the distinction between how precisely an array-element
 360 // is tracked is irrelevant here.)
 361 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 362 pub enum InteriorKind {
 363     InteriorField(mc::FieldIndex),
 364     InteriorElement,
 365 }
 366
 367 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 368 impl ToInteriorKind for mc::InteriorKind {
 369     fn cleaned(self) -> InteriorKind {
 370         match self {
 371             mc::InteriorField(name) => InteriorField(name),
 372             mc::InteriorElement(_) => InteriorElement,
 373         }
 374     }
 375 }
 376
 377 // This can be:
 378 // - a pointer dereference (`*P` in README.md)
 379 // - a field reference, with an optional definition of the containing
 380 //   enum variant (`P.f` in README.md)
 381 // `DefId` is present when the field is part of struct that is in
 382 // a variant of an enum. For instance in:
 383 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 384 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 385 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 386 pub enum LoanPathElem<'tcx> {
 387     LpDeref(mc::PointerKind<'tcx>),
 388     LpInterior(Option<DefId>, InteriorKind),
 389 }
 390
 391 fn closure_to_block(closure_id: LocalDefId, tcx: TyCtxt<'_, '_>) -> HirId {
 392     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 393     match tcx.hir().get(closure_id) {
 394         Node::Expr(expr) => match expr.node {
 395             hir::ExprKind::Closure(.., body_id, _, _) => {
 396                 body_id.hir_id
 397             }
 398             _ => {
 399                 bug!("encountered non-closure id: {}", closure_id)
 400             }
 401         },
 402         _ => bug!("encountered non-expr id: {}", closure_id)
 403     }
 404 }
 405
 406 impl LoanPath<'tcx> {
 407     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'_, 'tcx>) -> region::Scope {
 408         match self.kind {
 409             LpVar(hir_id) => {
 410                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 411             }
 412             LpUpvar(upvar_id) => {
 413                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 414                 region::Scope { id: block_id.local_id, data: region::ScopeData::Node }
 415             }
 416             LpDowncast(ref base, _) |
 417             LpExtend(ref base, ..) => base.kill_scope(bccx),
 418         }
 419     }
 420
 421     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 422         match (&self.kind, &other.kind) {
 423             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 424              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 425                 if id == id2 && opt_variant_id == opt_variant_id2 {
 426                     base.has_fork(&base2)
 427                 } else {
 428                     true
 429                 },
 430             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 431             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 432             _ => false,
 433         }
 434     }
 435
 436     fn depth(&self) -> usize {
 437         match self.kind {
 438             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 439             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 440             _ => 0,
 441         }
 442     }
 443
 444     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 445         match (&self.kind, &other.kind) {
 446             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 447              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 448                 if id == id2 && opt_variant_id == opt_variant_id2 {
 449                     base.common(&base2).map(|x| {
 450                         let xd = x.depth();
 451                         if base.depth() == xd && base2.depth() == xd {
 452                             LoanPath {
 453                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 454                                 ty: self.ty,
 455                             }
 456                         } else {
 457                             x
 458                         }
 459                     })
 460                 } else {
 461                     base.common(&base2)
 462                 }
 463             }
 464             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 465             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 466             (&LpVar(id), &LpVar(id2)) => {
 467                 if id == id2 {
 468                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 469                 } else {
 470                     None
 471                 }
 472             }
 473             (&LpUpvar(id), &LpUpvar(id2)) => {
 474                 if id == id2 {
 475                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 476                 } else {
 477                     None
 478                 }
 479             }
 480             _ => None,
 481         }
 482     }
 483 }
 484
 485 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 486 // mutable independently of the struct it belongs to. (#35937)
 487 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 488     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 489
 490     match cmt.cat {
 491         Categorization::Rvalue(..) |
 492         Categorization::ThreadLocal(..) |
 493         Categorization::StaticItem => {
 494             (None, false)
 495         }
 496
 497         Categorization::Local(id) => {
 498             (Some(new_lp(LpVar(id))), false)
 499         }
 500
 501         Categorization::Upvar(mc::Upvar { id, .. }) => {
 502             (Some(new_lp(LpUpvar(id))), false)
 503         }
 504
 505         Categorization::Deref(ref cmt_base, pk) => {
 506             let lp = opt_loan_path_is_field(cmt_base);
 507             (lp.0.map(|lp| {
 508                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 509             }), lp.1)
 510         }
 511
 512         Categorization::Interior(ref cmt_base, ik) => {
 513             (opt_loan_path(cmt_base).map(|lp| {
 514                 let opt_variant_id = match cmt_base.cat {
 515                     Categorization::Downcast(_, did) =>  Some(did),
 516                     _ => None
 517                 };
 518                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 519             }), true)
 520         }
 521
 522         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 523             let lp = opt_loan_path_is_field(cmt_base);
 524             (lp.0.map(|lp| {
 525                 new_lp(LpDowncast(lp, variant_def_id))
 526             }), lp.1)
 527         }
 528     }
 529 }
 530
 531 /// Computes the `LoanPath` (if any) for a `cmt`.
 532 /// Note that this logic is somewhat duplicated in
 533 /// the method `compute()` found in `gather_loans::restrictions`,
 534 /// which allows it to share common loan path pieces as it
 535 /// traverses the CMT.
 536 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 537     opt_loan_path_is_field(cmt).0
 538 }
 539
 540 ///////////////////////////////////////////////////////////////////////////
 541 // Errors
 542
 543 // Errors that can occur
 544 #[derive(Debug, PartialEq)]
 545 pub enum bckerr_code<'tcx> {
 546     err_mutbl,
 547     /// superscope, subscope, loan cause
 548     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 549     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 550 }
 551
 552 // Combination of an error code and the categorization of the expression
 553 // that caused it
 554 #[derive(Debug, PartialEq)]
 555 pub struct BckError<'c, 'tcx: 'c> {
 556     span: Span,
 557     cause: AliasableViolationKind,
 558     cmt: &'c mc::cmt_<'tcx>,
 559     code: bckerr_code<'tcx>
 560 }
 561
 562 #[derive(Copy, Clone, Debug, PartialEq)]
 563 pub enum AliasableViolationKind {
 564     MutabilityViolation,
 565     BorrowViolation(euv::LoanCause)
 566 }
 567
 568 #[derive(Copy, Clone, Debug)]
 569 pub enum MovedValueUseKind {
 570     MovedInUse,
 571     MovedInCapture,
 572 }
 573
 574 ///////////////////////////////////////////////////////////////////////////
 575 // Misc
 576
 577 impl BorrowckCtxt<'_, 'tcx> {
 578     pub fn is_subregion_of(&self,
 579                            r_sub: ty::Region<'tcx>,
 580                            r_sup: ty::Region<'tcx>)
 581                            -> bool
 582     {
 583         let region_rels = RegionRelations::new(self.tcx,
 584                                                self.owner_def_id,
 585                                                &self.region_scope_tree,
 586                                                &self.tables.free_region_map);
 587         region_rels.is_subregion_of(r_sub, r_sup)
 588     }
 589
 590     pub fn report(&self, err: BckError<'a, 'tcx>) {
 591         // Catch and handle some particular cases.
 592         match (&err.code, &err.cause) {
 593             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 594              &BorrowViolation(euv::ClosureCapture(span))) |
 595             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 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         self.report_bckerr(&err);
 605     }
 606
 607     pub fn report_use_of_moved_value(&self,
 608                                      use_span: Span,
 609                                      use_kind: MovedValueUseKind,
 610                                      lp: &LoanPath<'tcx>,
 611                                      the_move: &move_data::Move,
 612                                      moved_lp: &LoanPath<'tcx>) {
 613         let (verb, verb_participle) = match use_kind {
 614             MovedInUse => ("use", "used"),
 615             MovedInCapture => ("capture", "captured"),
 616         };
 617
 618         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 619             move_data::Declared => {
 620                 // If this is an uninitialized variable, just emit a simple warning
 621                 // and return.
 622                 self.cannot_act_on_uninitialized_variable(use_span,
 623                                                           verb,
 624                                                           &self.loan_path_to_string(lp),
 625                                                           Origin::Ast)
 626                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 627                                                   self.loan_path_to_string(lp)))
 628                     .emit();
 629                 self.signal_error();
 630                 return;
 631             }
 632             _ => {
 633                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 634                 // normally generate a rather confusing message:
 635                 //
 636                 //     error: use of moved value: `x.b`
 637                 //     note: `x.a` moved here...
 638                 //
 639                 // What we want to do instead is get the 'common ancestor' of the two moves and
 640                 // use that for most of the message instead, giving is something like this:
 641                 //
 642                 //     error: use of moved value: `x`
 643                 //     note: `x` moved here (through moving `x.a`)...
 644
 645                 let common = moved_lp.common(lp);
 646                 let has_common = common.is_some();
 647                 let has_fork = moved_lp.has_fork(lp);
 648                 let (nl, ol, moved_lp_msg) =
 649                     if has_fork && has_common {
 650                         let nl = self.loan_path_to_string(&common.unwrap());
 651                         let ol = nl.clone();
 652                         let moved_lp_msg = format!(" (through moving `{}`)",
 653                                                    self.loan_path_to_string(moved_lp));
 654                         (nl, ol, moved_lp_msg)
 655                     } else {
 656                         (self.loan_path_to_string(lp),
 657                          self.loan_path_to_string(moved_lp),
 658                          String::new())
 659                     };
 660
 661                 let partial = moved_lp.depth() > lp.depth();
 662                 let msg = if !has_fork && partial { "partially " }
 663                           else if has_fork && !has_common { "collaterally "}
 664                 else { "" };
 665                 let mut err = self.cannot_act_on_moved_value(use_span,
 666                                                              verb,
 667                                                              msg,
 668                                                              Some(nl),
 669                                                              Origin::Ast);
 670                 let need_note = match lp.ty.sty {
 671                     ty::Closure(id, _) => {
 672                         let hir_id = self.tcx.hir().as_local_hir_id(id).unwrap();
 673                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 674                             err.span_note(*span, &format!(
 675                                 "closure cannot be invoked more than once because \
 676                                 it moves the variable `{}` out of its environment",
 677                                 name
 678                             ));
 679                             false
 680                         } else {
 681                             true
 682                         }
 683                     }
 684                     _ => true,
 685                 };
 686                 (ol, moved_lp_msg, err, need_note)
 687             }
 688         };
 689
 690         // Get type of value and span where it was previously
 691         // moved.
 692         let hir_id = hir::HirId {
 693             owner: self.body.value.hir_id.owner,
 694             local_id: the_move.id
 695         };
 696         let (move_span, move_note) = match the_move.kind {
 697             move_data::Declared => {
 698                 unreachable!();
 699             }
 700
 701             move_data::MoveExpr |
 702             move_data::MovePat => (self.tcx.hir().span_by_hir_id(hir_id), ""),
 703
 704             move_data::Captured =>
 705                 (match self.tcx.hir().expect_expr_by_hir_id(hir_id).node {
 706                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 707                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 708                                   the_move.id, r),
 709                 }, " (into closure)"),
 710         };
 711
 712         // Annotate the use and the move in the span. Watch out for
 713         // the case where the use and the move are the same. This
 714         // means the use is in a loop.
 715         err = if use_span == move_span {
 716             err.span_label(
 717                 use_span,
 718                 format!("value moved{} here in previous iteration of loop",
 719                          move_note));
 720             err
 721         } else {
 722             err.span_label(use_span, format!("value {} here after move", verb_participle));
 723             err.span_label(move_span, format!("value moved{} here", move_note));
 724             err
 725         };
 726
 727         if need_note {
 728             err.note(&format!(
 729                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 730                 if moved_lp.has_downcast() {
 731                     "the value".to_string()
 732                 } else {
 733                     format!("`{}`", self.loan_path_to_string(moved_lp))
 734                 },
 735                 moved_lp.ty));
 736         }
 737         if let (Some(CompilerDesugaringKind::ForLoop), Ok(snippet)) = (
 738             move_span.compiler_desugaring_kind(),
 739             self.tcx.sess.source_map().span_to_snippet(move_span),
 740          ) {
 741             if !snippet.starts_with("&") {
 742                 err.span_suggestion(
 743                     move_span,
 744                     "consider borrowing this to avoid moving it into the for loop",
 745                     format!("&{}", snippet),
 746                     Applicability::MaybeIncorrect,
 747                 );
 748             }
 749         }
 750
 751         // Note: we used to suggest adding a `ref binding` or calling
 752         // `clone` but those suggestions have been removed because
 753         // they are often not what you actually want to do, and were
 754         // not considered particularly helpful.
 755
 756         err.emit();
 757         self.signal_error();
 758     }
 759
 760     pub fn report_partial_reinitialization_of_uninitialized_structure(
 761             &self,
 762             span: Span,
 763             lp: &LoanPath<'tcx>) {
 764         self.cannot_partially_reinit_an_uninit_struct(span,
 765                                                       &self.loan_path_to_string(lp),
 766                                                       Origin::Ast)
 767             .emit();
 768         self.signal_error();
 769     }
 770
 771     pub fn report_reassigned_immutable_variable(&self,
 772                                                 span: Span,
 773                                                 lp: &LoanPath<'tcx>,
 774                                                 assign:
 775                                                 &move_data::Assignment) {
 776         let mut err = self.cannot_reassign_immutable(span,
 777                                                      &self.loan_path_to_string(lp),
 778                                                      false,
 779                                                      Origin::Ast);
 780         err.span_label(span, "cannot assign twice to immutable variable");
 781         if span != assign.span {
 782             err.span_label(assign.span, format!("first assignment to `{}`",
 783                                                 self.loan_path_to_string(lp)));
 784         }
 785         err.emit();
 786         self.signal_error();
 787     }
 788
 789     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 790         let error_span = err.span.clone();
 791
 792         match err.code {
 793             err_mutbl => {
 794                 let descr: Cow<'static, str> = match err.cmt.note {
 795                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 796                         self.cmt_to_cow_str(&err.cmt)
 797                     }
 798                     _ => match opt_loan_path_is_field(&err.cmt) {
 799                         (None, true) => {
 800                             format!("{} of {} binding",
 801                                     self.cmt_to_cow_str(&err.cmt),
 802                                     err.cmt.mutbl.to_user_str()).into()
 803
 804                         }
 805                         (None, false) => {
 806                             format!("{} {}",
 807                                     err.cmt.mutbl.to_user_str(),
 808                                     self.cmt_to_cow_str(&err.cmt)).into()
 809
 810                         }
 811                         (Some(lp), true) => {
 812                             format!("{} `{}` of {} binding",
 813                                     self.cmt_to_cow_str(&err.cmt),
 814                                     self.loan_path_to_string(&lp),
 815                                     err.cmt.mutbl.to_user_str()).into()
 816                         }
 817                         (Some(lp), false) => {
 818                             format!("{} {} `{}`",
 819                                     err.cmt.mutbl.to_user_str(),
 820                                     self.cmt_to_cow_str(&err.cmt),
 821                                     self.loan_path_to_string(&lp)).into()
 822                         }
 823                     }
 824                 };
 825
 826                 let mut db = match err.cause {
 827                     MutabilityViolation => {
 828                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 829                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 830                             let hir_id = upvar_id.var_path.hir_id;
 831                             let sp = self.tcx.hir().span_by_hir_id(hir_id);
 832                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 833                                                   environment for modifications";
 834                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 835                                 (_, &Categorization::Upvar(mc::Upvar {
 836                                     kind: ty::ClosureKind::Fn, ..
 837                                 })) => {
 838                                     db.note(fn_closure_msg);
 839                                     // we should point at the cause for this closure being
 840                                     // identified as `Fn` (like in signature of method this
 841                                     // closure was passed into)
 842                                 }
 843                                 (Ok(ref snippet), ref cat) => {
 844                                     let msg = &format!("consider making `{}` mutable", snippet);
 845                                     let suggestion = format!("mut {}", snippet);
 846
 847                                     if let &Categorization::Deref(ref cmt, _) = cat {
 848                                         if let Categorization::Upvar(mc::Upvar {
 849                                             kind: ty::ClosureKind::Fn, ..
 850                                         }) = cmt.cat {
 851                                             db.note(fn_closure_msg);
 852                                         } else {
 853                                             db.span_suggestion(
 854                                                 sp,
 855                                                 msg,
 856                                                 suggestion,
 857                                                 Applicability::Unspecified,
 858                                             );
 859                                         }
 860                                     } else {
 861                                         db.span_suggestion(
 862                                             sp,
 863                                             msg,
 864                                             suggestion,
 865                                             Applicability::Unspecified,
 866                                         );
 867                                     }
 868                                 }
 869                                 _ => {
 870                                     db.span_help(sp, "consider making this binding mutable");
 871                                 }
 872                             }
 873                         }
 874
 875                         db
 876                     }
 877                     BorrowViolation(euv::ClosureCapture(_)) => {
 878                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 879                     }
 880                     BorrowViolation(euv::OverloadedOperator) |
 881                     BorrowViolation(euv::AddrOf) |
 882                     BorrowViolation(euv::RefBinding) |
 883                     BorrowViolation(euv::AutoRef) |
 884                     BorrowViolation(euv::AutoUnsafe) |
 885                     BorrowViolation(euv::ForLoop) |
 886                     BorrowViolation(euv::MatchDiscriminant) => {
 887                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 888                     }
 889                     BorrowViolation(euv::ClosureInvocation) => {
 890                         span_bug!(err.span, "err_mutbl with a closure invocation");
 891                     }
 892                 };
 893
 894                 // We add a special note about `IndexMut`, if the source of this error
 895                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 896                 // to implement two traits for "one operator" is not very intuitive for
 897                 // many programmers.
 898                 if err.cmt.note == mc::NoteIndex {
 899                     let node_id = self.tcx.hir().hir_to_node_id(err.cmt.hir_id);
 900                     let node =  self.tcx.hir().get(node_id);
 901
 902                     // This pattern probably always matches.
 903                     if let Node::Expr(
 904                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 905                     ) = node {
 906                         let ty = self.tables.expr_ty(lhs);
 907
 908                         db.help(&format!(
 909                             "trait `IndexMut` is required to modify indexed content, but \
 910                              it is not implemented for `{}`",
 911                             ty
 912                         ));
 913                     }
 914                 }
 915
 916                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 917                 self.note_immutability_blame(
 918                     &mut db,
 919                     err.cmt.immutability_blame(),
 920                     err.cmt.hir_id
 921                 );
 922                 db.emit();
 923                 self.signal_error();
 924             }
 925             err_out_of_scope(super_scope, sub_scope, cause) => {
 926                 let msg = match opt_loan_path(&err.cmt) {
 927                     None => "borrowed value".to_string(),
 928                     Some(lp) => {
 929                         format!("`{}`", self.loan_path_to_string(&lp))
 930                     }
 931                 };
 932
 933                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 934                 let value_kind = match err.cmt.cat {
 935                     mc::Categorization::Rvalue(..) => "temporary value",
 936                     _ => "borrowed value",
 937                 };
 938
 939                 let is_closure = match cause {
 940                     euv::ClosureCapture(s) => {
 941                         // The primary span starts out as the closure creation point.
 942                         // Change the primary span here to highlight the use of the variable
 943                         // in the closure, because it seems more natural. Highlight
 944                         // closure creation point as a secondary span.
 945                         match db.span.primary_span() {
 946                             Some(primary) => {
 947                                 db.span = MultiSpan::from_span(s);
 948                                 db.span_label(primary, "capture occurs here");
 949                                 db.span_label(s, format!("{} does not live long enough",
 950                                                          value_kind));
 951                                 true
 952                             }
 953                             None => false
 954                         }
 955                     }
 956                     _ => {
 957                         db.span_label(error_span, format!("{} does not live long enough",
 958                                                           value_kind));
 959                         false
 960                     }
 961                 };
 962
 963                 let sub_span = self.region_end_span(sub_scope);
 964                 let super_span = self.region_end_span(super_scope);
 965
 966                 match (sub_span, super_span) {
 967                     (Some(s1), Some(s2)) if s1 == s2 => {
 968                         if !is_closure {
 969                             let msg = match opt_loan_path(&err.cmt) {
 970                                 None => value_kind.to_string(),
 971                                 Some(lp) => {
 972                                     format!("`{}`", self.loan_path_to_string(&lp))
 973                                 }
 974                             };
 975                             db.span_label(s1,
 976                                           format!("{} dropped here while still borrowed", msg));
 977                         } else {
 978                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 979                         }
 980                         db.note("values in a scope are dropped in the opposite order \
 981                                 they are created");
 982                     }
 983                     (Some(s1), Some(s2)) if !is_closure => {
 984                         let msg = match opt_loan_path(&err.cmt) {
 985                             None => value_kind.to_string(),
 986                             Some(lp) => {
 987                                 format!("`{}`", self.loan_path_to_string(&lp))
 988                             }
 989                         };
 990                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 991                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 992                     }
 993                     _ => {
 994                         match sub_span {
 995                             Some(s) => {
 996                                 db.span_label(s, format!("{} needs to live until here",
 997                                                           value_kind));
 998                             }
 999                             None => {
1000                                 self.tcx.note_and_explain_region(
1001                                     &self.region_scope_tree,
1002                                     &mut db,
1003                                     "borrowed value must be valid for ",
1004                                     sub_scope,
1005                                     "...");
1006                             }
1007                         }
1008                         match super_span {
1009                             Some(s) => {
1010                                 db.span_label(s, format!("{} only lives until here", value_kind));
1011                             }
1012                             None => {
1013                                 self.tcx.note_and_explain_region(
1014                                     &self.region_scope_tree,
1015                                     &mut db,
1016                                     "...but borrowed value is only valid for ",
1017                                     super_scope,
1018                                     "");
1019                             }
1020                         }
1021                     }
1022                 }
1023
1024                 if let ty::ReScope(scope) = *super_scope {
1025                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1026                     match self.tcx.hir().find(node_id) {
1027                         Some(Node::Stmt(_)) => {
1028                             if *sub_scope != ty::ReStatic {
1029                                 db.note("consider using a `let` binding to increase its lifetime");
1030                             }
1031
1032                         }
1033                         _ => {}
1034                     }
1035                 }
1036
1037                 db.emit();
1038                 self.signal_error();
1039             }
1040             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1041                 let descr = self.cmt_to_path_or_string(err.cmt);
1042                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1043                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1044                     Some(lp) => {
1045                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1046                     }
1047                     None => self.cmt_to_cow_str(&err.cmt)
1048                 };
1049                 self.tcx.note_and_explain_region(
1050                     &self.region_scope_tree,
1051                     &mut db,
1052                     &format!("{} would have to be valid for ",
1053                             descr),
1054                     loan_scope,
1055                     "...");
1056                 self.tcx.note_and_explain_region(
1057                     &self.region_scope_tree,
1058                     &mut db,
1059                     &format!("...but {} is only valid for ", descr),
1060                     ptr_scope,
1061                     "");
1062
1063                 db.emit();
1064                 self.signal_error();
1065             }
1066         }
1067     }
1068
1069     pub fn report_aliasability_violation(&self,
1070                                          span: Span,
1071                                          kind: AliasableViolationKind,
1072                                          cause: mc::AliasableReason,
1073                                          cmt: &mc::cmt_<'tcx>) {
1074         let mut is_closure = false;
1075         let prefix = match kind {
1076             MutabilityViolation => {
1077                 "cannot assign to data"
1078             }
1079             BorrowViolation(euv::ClosureCapture(_)) |
1080             BorrowViolation(euv::OverloadedOperator) |
1081             BorrowViolation(euv::AddrOf) |
1082             BorrowViolation(euv::AutoRef) |
1083             BorrowViolation(euv::AutoUnsafe) |
1084             BorrowViolation(euv::RefBinding) |
1085             BorrowViolation(euv::MatchDiscriminant) => {
1086                 "cannot borrow data mutably"
1087             }
1088             BorrowViolation(euv::ClosureInvocation) => {
1089                 is_closure = true;
1090                 "closure invocation"
1091             }
1092
1093             BorrowViolation(euv::ForLoop) => {
1094                 "`for` loop"
1095             }
1096         };
1097
1098         match cause {
1099             mc::AliasableStaticMut => {
1100                 // This path cannot occur. `static mut X` is not checked
1101                 // for aliasability violations.
1102                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1103             }
1104             mc::AliasableStatic | mc::AliasableBorrowed => {}
1105         };
1106         let blame = cmt.immutability_blame();
1107         let mut err = match blame {
1108             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1109                 // FIXME: the distinction between these 2 messages looks wrong.
1110                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1111                     // The aliasability violation with closure captures can
1112                     // happen for nested closures, so we know the enclosing
1113                     // closure incorrectly accepts an `Fn` while it needs to
1114                     // be `FnMut`.
1115                     "consider changing this to accept closures that implement `FnMut`"
1116
1117                 } else {
1118                     "consider changing this closure to take self by mutable reference"
1119                 };
1120                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(id);
1121                 let help_span = self.tcx.hir().span_by_hir_id(hir_id);
1122                 self.cannot_act_on_capture_in_sharable_fn(span,
1123                                                           prefix,
1124                                                           (help_span, help_msg),
1125                                                           Origin::Ast)
1126             }
1127             _ =>  {
1128                 self.cannot_assign_into_immutable_reference(span, prefix,
1129                                                             Origin::Ast)
1130             }
1131         };
1132         self.note_immutability_blame(
1133             &mut err,
1134             blame,
1135             cmt.hir_id
1136         );
1137
1138         if is_closure {
1139             err.help("closures behind references must be called via `&mut`");
1140         }
1141         err.emit();
1142         self.signal_error();
1143     }
1144
1145     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1146     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1147         // Check whether the argument is an immutable reference
1148         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1149         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1150             mutbl: hir::Mutability::MutImmutable,
1151             ref ty
1152         }) = pty.node {
1153             // Account for existing lifetimes when generating the message
1154             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1155                 Ok(snippet) => snippet,
1156                 _ => return None
1157             };
1158
1159             let lifetime_snippet = if !lifetime.is_elided() {
1160                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1161                     Ok(lifetime_snippet) => lifetime_snippet,
1162                     _ => return None
1163                 })
1164             } else {
1165                 String::new()
1166             };
1167             Some(format!("use `&{}mut {}` here to make mutable",
1168                          lifetime_snippet,
1169                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1170         } else {
1171             None
1172         }
1173     }
1174
1175     fn local_binding_mode(&self, hir_id: hir::HirId) -> ty::BindingMode {
1176         let pat = match self.tcx.hir().get_by_hir_id(hir_id) {
1177             Node::Binding(pat) => pat,
1178             node => bug!("bad node for local: {:?}", node)
1179         };
1180
1181         match pat.node {
1182             hir::PatKind::Binding(..) => {
1183                 *self.tables
1184                      .pat_binding_modes()
1185                      .get(pat.hir_id)
1186                      .expect("missing binding mode")
1187             }
1188             _ => bug!("local is not a binding: {:?}", pat)
1189         }
1190     }
1191
1192     fn local_ty(&self, hir_id: hir::HirId) -> (Option<&hir::Ty>, bool) {
1193         let parent = self.tcx.hir().get_parent_node_by_hir_id(hir_id);
1194         let parent_node = self.tcx.hir().get_by_hir_id(parent);
1195
1196         // The parent node is like a fn
1197         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1198             // `nid`'s parent's `Body`
1199             let fn_body = self.tcx.hir().body(fn_like.body());
1200             // Get the position of `node_id` in the arguments list
1201             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.hir_id == hir_id);
1202             if let Some(i) = arg_pos {
1203                 // The argument's `Ty`
1204                 (Some(&fn_like.decl().inputs[i]),
1205                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1206             } else {
1207                 (None, false)
1208             }
1209         } else {
1210             (None, false)
1211         }
1212     }
1213
1214     fn note_immutability_blame(&self,
1215                                db: &mut DiagnosticBuilder<'_>,
1216                                blame: Option<ImmutabilityBlame<'_>>,
1217                                error_hir_id: hir::HirId) {
1218         match blame {
1219             None => {}
1220             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1221             Some(ImmutabilityBlame::ImmLocal(hir_id)) => {
1222                 self.note_immutable_local(db, error_hir_id, hir_id)
1223             }
1224             Some(ImmutabilityBlame::LocalDeref(hir_id)) => {
1225                 match self.local_binding_mode(hir_id) {
1226                     ty::BindByReference(..) => {
1227                         let let_span = self.tcx.hir().span_by_hir_id(hir_id);
1228                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1229                         if let Some(replace_str) = suggestion {
1230                             db.span_suggestion(
1231                                 let_span,
1232                                 "use a mutable reference instead",
1233                                 replace_str,
1234                                 // I believe this can be machine applicable,
1235                                 // but if there are multiple attempted uses of an immutable
1236                                 // reference, I don't know how rustfix handles it, it might
1237                                 // attempt fixing them multiple times.
1238                                 //                              @estebank
1239                                 Applicability::Unspecified,
1240                             );
1241                         }
1242                     }
1243                     ty::BindByValue(..) => {
1244                         if let (Some(local_ty), is_implicit_self) = self.local_ty(hir_id) {
1245                             if let Some(msg) =
1246                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1247                                 db.span_label(local_ty.span, msg);
1248                             }
1249                         }
1250                     }
1251                 }
1252             }
1253             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1254                 let hir_id = match self.tcx.hir().as_local_hir_id(field.did) {
1255                     Some(hir_id) => hir_id,
1256                     None => return
1257                 };
1258
1259                 if let Node::Field(ref field) = self.tcx.hir().get_by_hir_id(hir_id) {
1260                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1261                         db.span_label(field.ty.span, msg);
1262                     }
1263                 }
1264             }
1265         }
1266     }
1267
1268      // Suggest a fix when trying to mutably borrow an immutable local
1269      // binding: either to make the binding mutable (if its type is
1270      // not a mutable reference) or to avoid borrowing altogether
1271     fn note_immutable_local(&self,
1272                             db: &mut DiagnosticBuilder<'_>,
1273                             borrowed_hir_id: hir::HirId,
1274                             binding_hir_id: hir::HirId) {
1275         let let_span = self.tcx.hir().span_by_hir_id(binding_hir_id);
1276         if let ty::BindByValue(..) = self.local_binding_mode(binding_hir_id) {
1277             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1278                 let (ty, is_implicit_self) = self.local_ty(binding_hir_id);
1279                 if is_implicit_self && snippet != "self" {
1280                     // avoid suggesting `mut &self`.
1281                     return
1282                 }
1283                 if let Some(&hir::TyKind::Rptr(
1284                     _,
1285                     hir::MutTy {
1286                         mutbl: hir::MutMutable,
1287                         ..
1288                     },
1289                 )) = ty.map(|t| &t.node)
1290                 {
1291                     let borrow_expr_id = self.tcx.hir().get_parent_node_by_hir_id(borrowed_hir_id);
1292                     db.span_suggestion(
1293                         self.tcx.hir().span_by_hir_id(borrow_expr_id),
1294                         "consider removing the `&mut`, as it is an \
1295                         immutable binding to a mutable reference",
1296                         snippet,
1297                         Applicability::MachineApplicable,
1298                     );
1299                 } else {
1300                     db.span_suggestion(
1301                         let_span,
1302                         "make this binding mutable",
1303                         format!("mut {}", snippet),
1304                         Applicability::MachineApplicable,
1305                     );
1306                 }
1307             }
1308         }
1309     }
1310
1311     fn report_out_of_scope_escaping_closure_capture(&self,
1312                                                     err: &BckError<'a, 'tcx>,
1313                                                     capture_span: Span)
1314     {
1315         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1316
1317         let suggestion =
1318             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1319                 Ok(string) => format!("move {}", string),
1320                 Err(_) => "move |<args>| <body>".to_string()
1321             };
1322
1323         self.cannot_capture_in_long_lived_closure(err.span,
1324                                                   &cmt_path_or_string,
1325                                                   capture_span,
1326                                                   Origin::Ast)
1327             .span_suggestion(
1328                  err.span,
1329                  &format!("to force the closure to take ownership of {} \
1330                            (and any other referenced variables), \
1331                            use the `move` keyword",
1332                            cmt_path_or_string),
1333                  suggestion,
1334                  Applicability::MachineApplicable,
1335             )
1336             .emit();
1337         self.signal_error();
1338     }
1339
1340     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1341         match *region {
1342             ty::ReScope(scope) => {
1343                 Some(self.tcx.sess.source_map().end_point(
1344                         scope.span(self.tcx, &self.region_scope_tree)))
1345             }
1346             _ => None
1347         }
1348     }
1349
1350     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder<'_>, err: &BckError<'a, 'tcx>,
1351                                     error_span: &Span) {
1352         match err.cmt.note {
1353             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1354                 // If this is an `Fn` closure, it simply can't mutate upvars.
1355                 // If it's an `FnMut` closure, the original variable was declared immutable.
1356                 // We need to determine which is the case here.
1357                 let kind = match err.cmt.upvar_cat().unwrap() {
1358                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1359                     _ => bug!()
1360                 };
1361                 if *kind == ty::ClosureKind::Fn {
1362                     let closure_hir_id =
1363                         self.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id);
1364                     db.span_help(self.tcx.hir().span_by_hir_id(closure_hir_id),
1365                                  "consider changing this closure to take \
1366                                   self by mutable reference");
1367                 }
1368             }
1369             _ => {
1370                 if let Categorization::Deref(..) = err.cmt.cat {
1371                     db.span_label(*error_span, "cannot borrow as mutable");
1372                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1373                     let span = self.tcx.hir().span_by_hir_id(local_id);
1374                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1375                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1376                             db.span_label(*error_span, "cannot reborrow mutably");
1377                             db.span_label(*error_span, "try removing `&mut` here");
1378                         } else {
1379                             db.span_label(*error_span, "cannot borrow mutably");
1380                         }
1381                     } else {
1382                         db.span_label(*error_span, "cannot borrow mutably");
1383                     }
1384                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1385                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1386                         db.span_label(*error_span,
1387                                       "cannot mutably borrow field of immutable binding");
1388                     }
1389                 }
1390             }
1391         }
1392     }
1393     pub fn append_loan_path_to_string(&self,
1394                                       loan_path: &LoanPath<'tcx>,
1395                                       out: &mut String) {
1396         match loan_path.kind {
1397             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id }, closure_expr_id: _ }) => {
1398                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1399             }
1400             LpVar(id) => {
1401                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1402             }
1403
1404             LpDowncast(ref lp_base, variant_def_id) => {
1405                 out.push('(');
1406                 self.append_loan_path_to_string(&lp_base, out);
1407                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1408                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1409                 out.push(')');
1410             }
1411
1412             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1413                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1414                 out.push('.');
1415                 out.push_str(&info.as_str());
1416             }
1417
1418             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1419                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1420                 out.push_str("[..]");
1421             }
1422
1423             LpExtend(ref lp_base, _, LpDeref(_)) => {
1424                 out.push('*');
1425                 self.append_loan_path_to_string(&lp_base, out);
1426             }
1427         }
1428     }
1429
1430     pub fn append_autoderefd_loan_path_to_string(&self,
1431                                                  loan_path: &LoanPath<'tcx>,
1432                                                  out: &mut String) {
1433         match loan_path.kind {
1434             LpExtend(ref lp_base, _, LpDeref(_)) => {
1435                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1436                 // rules would normally allow users to omit the `*x`.
1437                 // So just serialize such paths to `x.f` or x[3]` respectively.
1438                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1439             }
1440
1441             LpDowncast(ref lp_base, variant_def_id) => {
1442                 out.push('(');
1443                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1444                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1445                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1446                 out.push(')');
1447             }
1448
1449             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1450                 self.append_loan_path_to_string(loan_path, out)
1451             }
1452         }
1453     }
1454
1455     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1456         let mut result = String::new();
1457         self.append_loan_path_to_string(loan_path, &mut result);
1458         result
1459     }
1460
1461     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1462         cmt.descriptive_string(self.tcx)
1463     }
1464
1465     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1466         match opt_loan_path(cmt) {
1467             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1468             None => self.cmt_to_cow_str(cmt).into_owned(),
1469         }
1470     }
1471 }
1472
1473 impl BitwiseOperator for LoanDataFlowOperator {
1474     #[inline]
1475     fn join(&self, succ: usize, pred: usize) -> usize {
1476         succ | pred // loans from both preds are in scope
1477     }
1478 }
1479
1480 impl DataFlowOperator for LoanDataFlowOperator {
1481     #[inline]
1482     fn initial_value(&self) -> bool {
1483         false // no loans in scope by default
1484     }
1485 }
1486
1487 impl fmt::Debug for InteriorKind {
1488     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1489         match *self {
1490             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1491             InteriorElement => write!(f, "[]"),
1492         }
1493     }
1494 }
1495
1496 impl<'tcx> fmt::Debug for Loan<'tcx> {
1497     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1498         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1499                self.index,
1500                self.loan_path,
1501                self.kind,
1502                self.gen_scope,
1503                self.kill_scope,
1504                self.restricted_paths)
1505     }
1506 }
1507
1508 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1509     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1510         match self.kind {
1511             LpVar(id) => {
1512                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_string(id)))
1513             }
1514
1515             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1516                 let s = ty::tls::with(|tcx| {
1517                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1518                     tcx.hir().node_to_string(var_node_id)
1519                 });
1520                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1521             }
1522
1523             LpDowncast(ref lp, variant_def_id) => {
1524                 let variant_str = if variant_def_id.is_local() {
1525                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1526                 } else {
1527                     format!("{:?}", variant_def_id)
1528                 };
1529                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1530             }
1531
1532             LpExtend(ref lp, _, LpDeref(_)) => {
1533                 write!(f, "{:?}.*", lp)
1534             }
1535
1536             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1537                 write!(f, "{:?}.{:?}", lp, interior)
1538             }
1539         }
1540     }
1541 }
1542
1543 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1544     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1545         match self.kind {
1546             LpVar(id) => {
1547                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_user_string(id)))
1548             }
1549
1550             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1551                 let s = ty::tls::with(|tcx| {
1552                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1553                     tcx.hir().node_to_string(var_node_id)
1554                 });
1555                 write!(f, "$({} captured by closure)", s)
1556             }
1557
1558             LpDowncast(ref lp, variant_def_id) => {
1559                 let variant_str = if variant_def_id.is_local() {
1560                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1561                 } else {
1562                     format!("{:?}", variant_def_id)
1563                 };
1564                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1565             }
1566
1567             LpExtend(ref lp, _, LpDeref(_)) => {
1568                 write!(f, "{}.*", lp)
1569             }
1570
1571             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1572                 write!(f, "{}.{:?}", lp, interior)
1573             }
1574         }
1575     }
1576 }