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 rustc_data_structures::sync::Lrc;
  36 use std::hash::{Hash, Hasher};
  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 mod unused;
  52
  53 #[derive(Clone, Copy)]
  54 pub struct LoanDataFlowOperator;
  55
  56 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  57
  58 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  59     tcx.par_body_owners(|body_owner_def_id| {
  60         tcx.ensure().borrowck(body_owner_def_id);
  61     });
  62 }
  63
  64 pub fn provide(providers: &mut Providers<'_>) {
  65     *providers = Providers {
  66         borrowck,
  67         ..*providers
  68     };
  69 }
  70
  71 /// Collection of conclusions determined via borrow checker analyses.
  72 pub struct AnalysisData<'a, 'tcx: 'a> {
  73     pub all_loans: Vec<Loan<'tcx>>,
  74     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  75     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  76 }
  77
  78 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  79     -> Lrc<BorrowCheckResult>
  80 {
  81     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  82
  83     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  84
  85     let owner_id = tcx.hir().as_local_hir_id(owner_def_id).unwrap();
  86
  87     match tcx.hir().get_by_hir_id(owner_id) {
  88         Node::StructCtor(_) |
  89         Node::Variant(_) => {
  90             // We get invoked with anything that has MIR, but some of
  91             // those things (notably the synthesized constructors from
  92             // tuple structs/variants) do not have an associated body
  93             // and do not need borrowchecking.
  94             return Lrc::new(BorrowCheckResult {
  95                 used_mut_nodes: Default::default(),
  96                 signalled_any_error: SignalledError::NoErrorsSeen,
  97             })
  98         }
  99         _ => { }
 100     }
 101
 102     let body_id = tcx.hir().body_owned_by(owner_id);
 103     let tables = tcx.typeck_tables_of(owner_def_id);
 104     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 105     let body = tcx.hir().body(body_id);
 106     let mut bccx = BorrowckCtxt {
 107         tcx,
 108         tables,
 109         region_scope_tree,
 110         owner_def_id,
 111         body,
 112         used_mut_nodes: Default::default(),
 113         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 114     };
 115
 116     // Eventually, borrowck will always read the MIR, but at the
 117     // moment we do not. So, for now, we always force MIR to be
 118     // constructed for a given fn, since this may result in errors
 119     // being reported and we want that to happen.
 120     //
 121     // Note that `mir_validated` is a "stealable" result; the
 122     // thief, `optimized_mir()`, forces borrowck, so we know that
 123     // is not yet stolen.
 124     tcx.ensure().mir_validated(owner_def_id);
 125
 126     // option dance because you can't capture an uninitialized variable
 127     // by mut-ref.
 128     let mut cfg = None;
 129     if let Some(AnalysisData { all_loans,
 130                                loans: loan_dfcx,
 131                                move_data: flowed_moves }) =
 132         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 133                                      |bccx| {
 134                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 135                                          cfg.as_mut().unwrap()
 136                                      })
 137     {
 138         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 139     }
 140
 141     if !tcx.use_mir_borrowck() {
 142         unused::check(&mut bccx, body);
 143     }
 144
 145     Lrc::new(BorrowCheckResult {
 146         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 147         signalled_any_error: bccx.signalled_any_error.into_inner(),
 148     })
 149 }
 150
 151 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 152                                                  force_analysis: bool,
 153                                                  body_id: hir::BodyId,
 154                                                  get_cfg: F)
 155                                                  -> Option<AnalysisData<'a, 'tcx>>
 156     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 157 {
 158     // Check the body of fn items.
 159     let (all_loans, move_data) =
 160         gather_loans::gather_loans_in_fn(this, body_id);
 161
 162     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 163         // large arrays of data inserted as constants can take a lot of
 164         // time and memory to borrow-check - see issue #36799. However,
 165         // they don't have places, so no borrow-check is actually needed.
 166         // Recognize that case and skip borrow-checking.
 167         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 168         return None;
 169     } else {
 170         debug!("propagating loans in {:?}", body_id);
 171     }
 172
 173     let cfg = get_cfg(this);
 174     let mut loan_dfcx =
 175         DataFlowContext::new(this.tcx,
 176                              "borrowck",
 177                              Some(this.body),
 178                              cfg,
 179                              LoanDataFlowOperator,
 180                              all_loans.len());
 181     for (loan_idx, loan) in all_loans.iter().enumerate() {
 182         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 183         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 184                            loan.kill_scope.item_local_id(),
 185                            loan_idx);
 186     }
 187     loan_dfcx.add_kills_from_flow_exits(cfg);
 188     loan_dfcx.propagate(cfg, this.body);
 189
 190     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 191                                                       this,
 192                                                       cfg,
 193                                                       this.body);
 194
 195     Some(AnalysisData { all_loans,
 196                         loans: loan_dfcx,
 197                         move_data:flowed_moves })
 198 }
 199
 200 /// Accessor for introspective clients inspecting `AnalysisData` and
 201 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 202 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 203     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 204     body_id: hir::BodyId,
 205     cfg: &cfg::CFG)
 206     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 207 {
 208     let owner_id = tcx.hir().body_owner(body_id);
 209     let owner_def_id = tcx.hir().local_def_id(owner_id);
 210     let tables = tcx.typeck_tables_of(owner_def_id);
 211     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 212     let body = tcx.hir().body(body_id);
 213     let mut bccx = BorrowckCtxt {
 214         tcx,
 215         tables,
 216         region_scope_tree,
 217         owner_def_id,
 218         body,
 219         used_mut_nodes: Default::default(),
 220         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 221     };
 222
 223     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 224     (bccx, dataflow_data.unwrap())
 225 }
 226
 227 // ----------------------------------------------------------------------
 228 // Type definitions
 229
 230 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 231     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 232
 233     // tables for the current thing we are checking; set to
 234     // Some in `borrowck_fn` and cleared later
 235     tables: &'a ty::TypeckTables<'tcx>,
 236
 237     region_scope_tree: Lrc<region::ScopeTree>,
 238
 239     owner_def_id: DefId,
 240
 241     body: &'tcx hir::Body,
 242
 243     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 244
 245     signalled_any_error: Cell<SignalledError>,
 246 }
 247
 248
 249 impl<'a, 'tcx: 'a> BorrowckCtxt<'a, 'tcx> {
 250     fn signal_error(&self) {
 251         self.signalled_any_error.set(SignalledError::SawSomeError);
 252     }
 253 }
 254
 255 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 256     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 257                                                      sp: S,
 258                                                      msg: &str,
 259                                                      code: DiagnosticId)
 260                                                      -> DiagnosticBuilder<'a>
 261     {
 262         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 263     }
 264
 265     fn struct_span_err<S: Into<MultiSpan>>(self,
 266                                            sp: S,
 267                                            msg: &str)
 268                                            -> DiagnosticBuilder<'a>
 269     {
 270         self.tcx.sess.struct_span_err(sp, msg)
 271     }
 272
 273     fn cancel_if_wrong_origin(self,
 274                               mut diag: DiagnosticBuilder<'a>,
 275                               o: Origin)
 276                               -> DiagnosticBuilder<'a>
 277     {
 278         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 279             self.tcx.sess.diagnostic().cancel(&mut diag);
 280         }
 281         diag
 282     }
 283 }
 284
 285 ///////////////////////////////////////////////////////////////////////////
 286 // Loans and loan paths
 287
 288 /// Record of a loan that was issued.
 289 pub struct Loan<'tcx> {
 290     index: usize,
 291     loan_path: Rc<LoanPath<'tcx>>,
 292     kind: ty::BorrowKind,
 293     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 294
 295     /// gen_scope indicates where loan is introduced. Typically the
 296     /// loan is introduced at the point of the borrow, but in some
 297     /// cases, notably method arguments, the loan may be introduced
 298     /// only later, once it comes into scope. See also
 299     /// `GatherLoanCtxt::compute_gen_scope`.
 300     gen_scope: region::Scope,
 301
 302     /// kill_scope indicates when the loan goes out of scope. This is
 303     /// either when the lifetime expires or when the local variable
 304     /// which roots the loan-path goes out of scope, whichever happens
 305     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 306     kill_scope: region::Scope,
 307     span: Span,
 308     cause: euv::LoanCause,
 309 }
 310
 311 impl<'tcx> Loan<'tcx> {
 312     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 313         self.loan_path.clone()
 314     }
 315 }
 316
 317 #[derive(Eq)]
 318 pub struct LoanPath<'tcx> {
 319     kind: LoanPathKind<'tcx>,
 320     ty: Ty<'tcx>,
 321 }
 322
 323 impl<'tcx> PartialEq for LoanPath<'tcx> {
 324     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 325         self.kind == that.kind
 326     }
 327 }
 328
 329 impl<'tcx> Hash for LoanPath<'tcx> {
 330     fn hash<H: Hasher>(&self, state: &mut H) {
 331         self.kind.hash(state);
 332     }
 333 }
 334
 335 #[derive(PartialEq, Eq, Hash, Debug)]
 336 pub enum LoanPathKind<'tcx> {
 337     LpVar(hir::HirId),                          // `x` in README.md
 338     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 339     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 340     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 341 }
 342
 343 impl<'tcx> LoanPath<'tcx> {
 344     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 345         LoanPath { kind: kind, ty: ty }
 346     }
 347
 348     fn to_type(&self) -> Ty<'tcx> { self.ty }
 349
 350     fn has_downcast(&self) -> bool {
 351         match self.kind {
 352             LpDowncast(_, _) => true,
 353             LpExtend(ref lp, _, LpInterior(_, _)) => {
 354                 lp.has_downcast()
 355             }
 356             _ => false,
 357         }
 358     }
 359 }
 360
 361 // FIXME (pnkfelix): See discussion here
 362 // https://github.com/pnkfelix/rust/commit/
 363 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 364 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 365
 366 // A local, "cleaned" version of `mc::InteriorKind` that drops
 367 // information that is not relevant to loan-path analysis. (In
 368 // particular, the distinction between how precisely an array-element
 369 // is tracked is irrelevant here.)
 370 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 371 pub enum InteriorKind {
 372     InteriorField(mc::FieldIndex),
 373     InteriorElement,
 374 }
 375
 376 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 377 impl ToInteriorKind for mc::InteriorKind {
 378     fn cleaned(self) -> InteriorKind {
 379         match self {
 380             mc::InteriorField(name) => InteriorField(name),
 381             mc::InteriorElement(_) => InteriorElement,
 382         }
 383     }
 384 }
 385
 386 // This can be:
 387 // - a pointer dereference (`*P` in README.md)
 388 // - a field reference, with an optional definition of the containing
 389 //   enum variant (`P.f` in README.md)
 390 // `DefId` is present when the field is part of struct that is in
 391 // a variant of an enum. For instance in:
 392 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 393 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 394 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 395 pub enum LoanPathElem<'tcx> {
 396     LpDeref(mc::PointerKind<'tcx>),
 397     LpInterior(Option<DefId>, InteriorKind),
 398 }
 399
 400 fn closure_to_block(closure_id: LocalDefId,
 401                     tcx: TyCtxt<'_, '_, '_>) -> HirId {
 402     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 403     match tcx.hir().get(closure_id) {
 404         Node::Expr(expr) => match expr.node {
 405             hir::ExprKind::Closure(.., body_id, _, _) => {
 406                 body_id.hir_id
 407             }
 408             _ => {
 409                 bug!("encountered non-closure id: {}", closure_id)
 410             }
 411         },
 412         _ => bug!("encountered non-expr id: {}", closure_id)
 413     }
 414 }
 415
 416 impl<'a, 'tcx> LoanPath<'tcx> {
 417     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 418         match self.kind {
 419             LpVar(hir_id) => {
 420                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 421             }
 422             LpUpvar(upvar_id) => {
 423                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 424                 region::Scope { id: block_id.local_id, data: region::ScopeData::Node }
 425             }
 426             LpDowncast(ref base, _) |
 427             LpExtend(ref base, ..) => base.kill_scope(bccx),
 428         }
 429     }
 430
 431     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 432         match (&self.kind, &other.kind) {
 433             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 434              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 435                 if id == id2 && opt_variant_id == opt_variant_id2 {
 436                     base.has_fork(&base2)
 437                 } else {
 438                     true
 439                 },
 440             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 441             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 442             _ => false,
 443         }
 444     }
 445
 446     fn depth(&self) -> usize {
 447         match self.kind {
 448             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 449             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 450             _ => 0,
 451         }
 452     }
 453
 454     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 455         match (&self.kind, &other.kind) {
 456             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 457              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 458                 if id == id2 && opt_variant_id == opt_variant_id2 {
 459                     base.common(&base2).map(|x| {
 460                         let xd = x.depth();
 461                         if base.depth() == xd && base2.depth() == xd {
 462                             LoanPath {
 463                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 464                                 ty: self.ty,
 465                             }
 466                         } else {
 467                             x
 468                         }
 469                     })
 470                 } else {
 471                     base.common(&base2)
 472                 }
 473             }
 474             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 475             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 476             (&LpVar(id), &LpVar(id2)) => {
 477                 if id == id2 {
 478                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 479                 } else {
 480                     None
 481                 }
 482             }
 483             (&LpUpvar(id), &LpUpvar(id2)) => {
 484                 if id == id2 {
 485                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 486                 } else {
 487                     None
 488                 }
 489             }
 490             _ => None,
 491         }
 492     }
 493 }
 494
 495 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 496 // mutable independently of the struct it belongs to. (#35937)
 497 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 498     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 499
 500     match cmt.cat {
 501         Categorization::Rvalue(..) |
 502         Categorization::ThreadLocal(..) |
 503         Categorization::StaticItem => {
 504             (None, false)
 505         }
 506
 507         Categorization::Local(id) => {
 508             (Some(new_lp(LpVar(id))), false)
 509         }
 510
 511         Categorization::Upvar(mc::Upvar { id, .. }) => {
 512             (Some(new_lp(LpUpvar(id))), false)
 513         }
 514
 515         Categorization::Deref(ref cmt_base, pk) => {
 516             let lp = opt_loan_path_is_field(cmt_base);
 517             (lp.0.map(|lp| {
 518                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 519             }), lp.1)
 520         }
 521
 522         Categorization::Interior(ref cmt_base, ik) => {
 523             (opt_loan_path(cmt_base).map(|lp| {
 524                 let opt_variant_id = match cmt_base.cat {
 525                     Categorization::Downcast(_, did) =>  Some(did),
 526                     _ => None
 527                 };
 528                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 529             }), true)
 530         }
 531
 532         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 533             let lp = opt_loan_path_is_field(cmt_base);
 534             (lp.0.map(|lp| {
 535                 new_lp(LpDowncast(lp, variant_def_id))
 536             }), lp.1)
 537         }
 538     }
 539 }
 540
 541 /// Computes the `LoanPath` (if any) for a `cmt`.
 542 /// Note that this logic is somewhat duplicated in
 543 /// the method `compute()` found in `gather_loans::restrictions`,
 544 /// which allows it to share common loan path pieces as it
 545 /// traverses the CMT.
 546 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 547     opt_loan_path_is_field(cmt).0
 548 }
 549
 550 ///////////////////////////////////////////////////////////////////////////
 551 // Errors
 552
 553 // Errors that can occur
 554 #[derive(Debug, PartialEq)]
 555 pub enum bckerr_code<'tcx> {
 556     err_mutbl,
 557     /// superscope, subscope, loan cause
 558     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 559     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 560 }
 561
 562 // Combination of an error code and the categorization of the expression
 563 // that caused it
 564 #[derive(Debug, PartialEq)]
 565 pub struct BckError<'c, 'tcx: 'c> {
 566     span: Span,
 567     cause: AliasableViolationKind,
 568     cmt: &'c mc::cmt_<'tcx>,
 569     code: bckerr_code<'tcx>
 570 }
 571
 572 #[derive(Copy, Clone, Debug, PartialEq)]
 573 pub enum AliasableViolationKind {
 574     MutabilityViolation,
 575     BorrowViolation(euv::LoanCause)
 576 }
 577
 578 #[derive(Copy, Clone, Debug)]
 579 pub enum MovedValueUseKind {
 580     MovedInUse,
 581     MovedInCapture,
 582 }
 583
 584 ///////////////////////////////////////////////////////////////////////////
 585 // Misc
 586
 587 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 588     pub fn is_subregion_of(&self,
 589                            r_sub: ty::Region<'tcx>,
 590                            r_sup: ty::Region<'tcx>)
 591                            -> bool
 592     {
 593         let region_rels = RegionRelations::new(self.tcx,
 594                                                self.owner_def_id,
 595                                                &self.region_scope_tree,
 596                                                &self.tables.free_region_map);
 597         region_rels.is_subregion_of(r_sub, r_sup)
 598     }
 599
 600     pub fn report(&self, err: BckError<'a, 'tcx>) {
 601         // Catch and handle some particular cases.
 602         match (&err.code, &err.cause) {
 603             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 604              &BorrowViolation(euv::ClosureCapture(span))) |
 605             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 606              &BorrowViolation(euv::ClosureCapture(span))) |
 607             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 608              &BorrowViolation(euv::ClosureCapture(span))) => {
 609                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 610             }
 611             _ => { }
 612         }
 613
 614         self.report_bckerr(&err);
 615     }
 616
 617     pub fn report_use_of_moved_value(&self,
 618                                      use_span: Span,
 619                                      use_kind: MovedValueUseKind,
 620                                      lp: &LoanPath<'tcx>,
 621                                      the_move: &move_data::Move,
 622                                      moved_lp: &LoanPath<'tcx>) {
 623         let (verb, verb_participle) = match use_kind {
 624             MovedInUse => ("use", "used"),
 625             MovedInCapture => ("capture", "captured"),
 626         };
 627
 628         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 629             move_data::Declared => {
 630                 // If this is an uninitialized variable, just emit a simple warning
 631                 // and return.
 632                 self.cannot_act_on_uninitialized_variable(use_span,
 633                                                           verb,
 634                                                           &self.loan_path_to_string(lp),
 635                                                           Origin::Ast)
 636                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 637                                                   self.loan_path_to_string(lp)))
 638                     .emit();
 639                 self.signal_error();
 640                 return;
 641             }
 642             _ => {
 643                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 644                 // normally generate a rather confusing message:
 645                 //
 646                 //     error: use of moved value: `x.b`
 647                 //     note: `x.a` moved here...
 648                 //
 649                 // What we want to do instead is get the 'common ancestor' of the two moves and
 650                 // use that for most of the message instead, giving is something like this:
 651                 //
 652                 //     error: use of moved value: `x`
 653                 //     note: `x` moved here (through moving `x.a`)...
 654
 655                 let common = moved_lp.common(lp);
 656                 let has_common = common.is_some();
 657                 let has_fork = moved_lp.has_fork(lp);
 658                 let (nl, ol, moved_lp_msg) =
 659                     if has_fork && has_common {
 660                         let nl = self.loan_path_to_string(&common.unwrap());
 661                         let ol = nl.clone();
 662                         let moved_lp_msg = format!(" (through moving `{}`)",
 663                                                    self.loan_path_to_string(moved_lp));
 664                         (nl, ol, moved_lp_msg)
 665                     } else {
 666                         (self.loan_path_to_string(lp),
 667                          self.loan_path_to_string(moved_lp),
 668                          String::new())
 669                     };
 670
 671                 let partial = moved_lp.depth() > lp.depth();
 672                 let msg = if !has_fork && partial { "partially " }
 673                           else if has_fork && !has_common { "collaterally "}
 674                 else { "" };
 675                 let mut err = self.cannot_act_on_moved_value(use_span,
 676                                                              verb,
 677                                                              msg,
 678                                                              Some(nl),
 679                                                              Origin::Ast);
 680                 let need_note = match lp.ty.sty {
 681                     ty::Closure(id, _) => {
 682                         let hir_id = self.tcx.hir().as_local_hir_id(id).unwrap();
 683                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 684                             err.span_note(*span, &format!(
 685                                 "closure cannot be invoked more than once because \
 686                                 it moves the variable `{}` out of its environment",
 687                                 name
 688                             ));
 689                             false
 690                         } else {
 691                             true
 692                         }
 693                     }
 694                     _ => true,
 695                 };
 696                 (ol, moved_lp_msg, err, need_note)
 697             }
 698         };
 699
 700         // Get type of value and span where it was previously
 701         // moved.
 702         let hir_id = hir::HirId {
 703             owner: self.body.value.hir_id.owner,
 704             local_id: the_move.id
 705         };
 706         let (move_span, move_note) = match the_move.kind {
 707             move_data::Declared => {
 708                 unreachable!();
 709             }
 710
 711             move_data::MoveExpr |
 712             move_data::MovePat => (self.tcx.hir().span_by_hir_id(hir_id), ""),
 713
 714             move_data::Captured =>
 715                 (match self.tcx.hir().expect_expr_by_hir_id(hir_id).node {
 716                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 717                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 718                                   the_move.id, r),
 719                 }, " (into closure)"),
 720         };
 721
 722         // Annotate the use and the move in the span. Watch out for
 723         // the case where the use and the move are the same. This
 724         // means the use is in a loop.
 725         err = if use_span == move_span {
 726             err.span_label(
 727                 use_span,
 728                 format!("value moved{} here in previous iteration of loop",
 729                          move_note));
 730             err
 731         } else {
 732             err.span_label(use_span, format!("value {} here after move", verb_participle));
 733             err.span_label(move_span, format!("value moved{} here", move_note));
 734             err
 735         };
 736
 737         if need_note {
 738             err.note(&format!(
 739                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 740                 if moved_lp.has_downcast() {
 741                     "the value".to_string()
 742                 } else {
 743                     format!("`{}`", self.loan_path_to_string(moved_lp))
 744                 },
 745                 moved_lp.ty));
 746         }
 747
 748         // Note: we used to suggest adding a `ref binding` or calling
 749         // `clone` but those suggestions have been removed because
 750         // they are often not what you actually want to do, and were
 751         // not considered particularly helpful.
 752
 753         err.emit();
 754         self.signal_error();
 755     }
 756
 757     pub fn report_partial_reinitialization_of_uninitialized_structure(
 758             &self,
 759             span: Span,
 760             lp: &LoanPath<'tcx>) {
 761         self.cannot_partially_reinit_an_uninit_struct(span,
 762                                                       &self.loan_path_to_string(lp),
 763                                                       Origin::Ast)
 764             .emit();
 765         self.signal_error();
 766     }
 767
 768     pub fn report_reassigned_immutable_variable(&self,
 769                                                 span: Span,
 770                                                 lp: &LoanPath<'tcx>,
 771                                                 assign:
 772                                                 &move_data::Assignment) {
 773         let mut err = self.cannot_reassign_immutable(span,
 774                                                      &self.loan_path_to_string(lp),
 775                                                      false,
 776                                                      Origin::Ast);
 777         err.span_label(span, "cannot assign twice to immutable variable");
 778         if span != assign.span {
 779             err.span_label(assign.span, format!("first assignment to `{}`",
 780                                                 self.loan_path_to_string(lp)));
 781         }
 782         err.emit();
 783         self.signal_error();
 784     }
 785
 786     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 787         let error_span = err.span.clone();
 788
 789         match err.code {
 790             err_mutbl => {
 791                 let descr: Cow<'static, str> = match err.cmt.note {
 792                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 793                         self.cmt_to_cow_str(&err.cmt)
 794                     }
 795                     _ => match opt_loan_path_is_field(&err.cmt) {
 796                         (None, true) => {
 797                             format!("{} of {} binding",
 798                                     self.cmt_to_cow_str(&err.cmt),
 799                                     err.cmt.mutbl.to_user_str()).into()
 800
 801                         }
 802                         (None, false) => {
 803                             format!("{} {}",
 804                                     err.cmt.mutbl.to_user_str(),
 805                                     self.cmt_to_cow_str(&err.cmt)).into()
 806
 807                         }
 808                         (Some(lp), true) => {
 809                             format!("{} `{}` of {} binding",
 810                                     self.cmt_to_cow_str(&err.cmt),
 811                                     self.loan_path_to_string(&lp),
 812                                     err.cmt.mutbl.to_user_str()).into()
 813                         }
 814                         (Some(lp), false) => {
 815                             format!("{} {} `{}`",
 816                                     err.cmt.mutbl.to_user_str(),
 817                                     self.cmt_to_cow_str(&err.cmt),
 818                                     self.loan_path_to_string(&lp)).into()
 819                         }
 820                     }
 821                 };
 822
 823                 let mut db = match err.cause {
 824                     MutabilityViolation => {
 825                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 826                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 827                             let hir_id = upvar_id.var_path.hir_id;
 828                             let sp = self.tcx.hir().span_by_hir_id(hir_id);
 829                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 830                                                   environment for modifications";
 831                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 832                                 (_, &Categorization::Upvar(mc::Upvar {
 833                                     kind: ty::ClosureKind::Fn, ..
 834                                 })) => {
 835                                     db.note(fn_closure_msg);
 836                                     // we should point at the cause for this closure being
 837                                     // identified as `Fn` (like in signature of method this
 838                                     // closure was passed into)
 839                                 }
 840                                 (Ok(ref snippet), ref cat) => {
 841                                     let msg = &format!("consider making `{}` mutable", snippet);
 842                                     let suggestion = format!("mut {}", snippet);
 843
 844                                     if let &Categorization::Deref(ref cmt, _) = cat {
 845                                         if let Categorization::Upvar(mc::Upvar {
 846                                             kind: ty::ClosureKind::Fn, ..
 847                                         }) = cmt.cat {
 848                                             db.note(fn_closure_msg);
 849                                         } else {
 850                                             db.span_suggestion(
 851                                                 sp,
 852                                                 msg,
 853                                                 suggestion,
 854                                                 Applicability::Unspecified,
 855                                             );
 856                                         }
 857                                     } else {
 858                                         db.span_suggestion(
 859                                             sp,
 860                                             msg,
 861                                             suggestion,
 862                                             Applicability::Unspecified,
 863                                         );
 864                                     }
 865                                 }
 866                                 _ => {
 867                                     db.span_help(sp, "consider making this binding mutable");
 868                                 }
 869                             }
 870                         }
 871
 872                         db
 873                     }
 874                     BorrowViolation(euv::ClosureCapture(_)) => {
 875                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 876                     }
 877                     BorrowViolation(euv::OverloadedOperator) |
 878                     BorrowViolation(euv::AddrOf) |
 879                     BorrowViolation(euv::RefBinding) |
 880                     BorrowViolation(euv::AutoRef) |
 881                     BorrowViolation(euv::AutoUnsafe) |
 882                     BorrowViolation(euv::ForLoop) |
 883                     BorrowViolation(euv::MatchDiscriminant) => {
 884                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 885                     }
 886                     BorrowViolation(euv::ClosureInvocation) => {
 887                         span_bug!(err.span,
 888                             "err_mutbl with a closure invocation");
 889                     }
 890                 };
 891
 892                 // We add a special note about `IndexMut`, if the source of this error
 893                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 894                 // to implement two traits for "one operator" is not very intuitive for
 895                 // many programmers.
 896                 if err.cmt.note == mc::NoteIndex {
 897                     let node_id = self.tcx.hir().hir_to_node_id(err.cmt.hir_id);
 898                     let node =  self.tcx.hir().get(node_id);
 899
 900                     // This pattern probably always matches.
 901                     if let Node::Expr(
 902                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 903                     ) = node {
 904                         let ty = self.tables.expr_ty(lhs);
 905
 906                         db.help(&format!(
 907                             "trait `IndexMut` is required to modify indexed content, but \
 908                              it is not implemented for `{}`",
 909                             ty
 910                         ));
 911                     }
 912                 }
 913
 914                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 915                 self.note_immutability_blame(
 916                     &mut db,
 917                     err.cmt.immutability_blame(),
 918                     err.cmt.hir_id
 919                 );
 920                 db.emit();
 921                 self.signal_error();
 922             }
 923             err_out_of_scope(super_scope, sub_scope, cause) => {
 924                 let msg = match opt_loan_path(&err.cmt) {
 925                     None => "borrowed value".to_string(),
 926                     Some(lp) => {
 927                         format!("`{}`", self.loan_path_to_string(&lp))
 928                     }
 929                 };
 930
 931                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 932                 let value_kind = match err.cmt.cat {
 933                     mc::Categorization::Rvalue(..) => "temporary value",
 934                     _ => "borrowed value",
 935                 };
 936
 937                 let is_closure = match cause {
 938                     euv::ClosureCapture(s) => {
 939                         // The primary span starts out as the closure creation point.
 940                         // Change the primary span here to highlight the use of the variable
 941                         // in the closure, because it seems more natural. Highlight
 942                         // closure creation point as a secondary span.
 943                         match db.span.primary_span() {
 944                             Some(primary) => {
 945                                 db.span = MultiSpan::from_span(s);
 946                                 db.span_label(primary, "capture occurs here");
 947                                 db.span_label(s, format!("{} does not live long enough",
 948                                                          value_kind));
 949                                 true
 950                             }
 951                             None => false
 952                         }
 953                     }
 954                     _ => {
 955                         db.span_label(error_span, format!("{} does not live long enough",
 956                                                           value_kind));
 957                         false
 958                     }
 959                 };
 960
 961                 let sub_span = self.region_end_span(sub_scope);
 962                 let super_span = self.region_end_span(super_scope);
 963
 964                 match (sub_span, super_span) {
 965                     (Some(s1), Some(s2)) if s1 == s2 => {
 966                         if !is_closure {
 967                             let msg = match opt_loan_path(&err.cmt) {
 968                                 None => value_kind.to_string(),
 969                                 Some(lp) => {
 970                                     format!("`{}`", self.loan_path_to_string(&lp))
 971                                 }
 972                             };
 973                             db.span_label(s1,
 974                                           format!("{} dropped here while still borrowed", msg));
 975                         } else {
 976                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 977                         }
 978                         db.note("values in a scope are dropped in the opposite order \
 979                                 they are created");
 980                     }
 981                     (Some(s1), Some(s2)) if !is_closure => {
 982                         let msg = match opt_loan_path(&err.cmt) {
 983                             None => value_kind.to_string(),
 984                             Some(lp) => {
 985                                 format!("`{}`", self.loan_path_to_string(&lp))
 986                             }
 987                         };
 988                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 989                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 990                     }
 991                     _ => {
 992                         match sub_span {
 993                             Some(s) => {
 994                                 db.span_label(s, format!("{} needs to live until here",
 995                                                           value_kind));
 996                             }
 997                             None => {
 998                                 self.tcx.note_and_explain_region(
 999                                     &self.region_scope_tree,
1000                                     &mut db,
1001                                     "borrowed value must be valid for ",
1002                                     sub_scope,
1003                                     "...");
1004                             }
1005                         }
1006                         match super_span {
1007                             Some(s) => {
1008                                 db.span_label(s, format!("{} only lives until here", value_kind));
1009                             }
1010                             None => {
1011                                 self.tcx.note_and_explain_region(
1012                                     &self.region_scope_tree,
1013                                     &mut db,
1014                                     "...but borrowed value is only valid for ",
1015                                     super_scope,
1016                                     "");
1017                             }
1018                         }
1019                     }
1020                 }
1021
1022                 if let ty::ReScope(scope) = *super_scope {
1023                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1024                     match self.tcx.hir().find(node_id) {
1025                         Some(Node::Stmt(_)) => {
1026                             if *sub_scope != ty::ReStatic {
1027                                 db.note("consider using a `let` binding to increase its lifetime");
1028                             }
1029
1030                         }
1031                         _ => {}
1032                     }
1033                 }
1034
1035                 db.emit();
1036                 self.signal_error();
1037             }
1038             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1039                 let descr = self.cmt_to_path_or_string(err.cmt);
1040                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1041                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1042                     Some(lp) => {
1043                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1044                     }
1045                     None => self.cmt_to_cow_str(&err.cmt)
1046                 };
1047                 self.tcx.note_and_explain_region(
1048                     &self.region_scope_tree,
1049                     &mut db,
1050                     &format!("{} would have to be valid for ",
1051                             descr),
1052                     loan_scope,
1053                     "...");
1054                 self.tcx.note_and_explain_region(
1055                     &self.region_scope_tree,
1056                     &mut db,
1057                     &format!("...but {} is only valid for ", descr),
1058                     ptr_scope,
1059                     "");
1060
1061                 db.emit();
1062                 self.signal_error();
1063             }
1064         }
1065     }
1066
1067     pub fn report_aliasability_violation(&self,
1068                                          span: Span,
1069                                          kind: AliasableViolationKind,
1070                                          cause: mc::AliasableReason,
1071                                          cmt: &mc::cmt_<'tcx>) {
1072         let mut is_closure = false;
1073         let prefix = match kind {
1074             MutabilityViolation => {
1075                 "cannot assign to data"
1076             }
1077             BorrowViolation(euv::ClosureCapture(_)) |
1078             BorrowViolation(euv::OverloadedOperator) |
1079             BorrowViolation(euv::AddrOf) |
1080             BorrowViolation(euv::AutoRef) |
1081             BorrowViolation(euv::AutoUnsafe) |
1082             BorrowViolation(euv::RefBinding) |
1083             BorrowViolation(euv::MatchDiscriminant) => {
1084                 "cannot borrow data mutably"
1085             }
1086
1087             BorrowViolation(euv::ClosureInvocation) => {
1088                 is_closure = true;
1089                 "closure invocation"
1090             }
1091
1092             BorrowViolation(euv::ForLoop) => {
1093                 "`for` loop"
1094             }
1095         };
1096
1097         match cause {
1098             mc::AliasableStaticMut => {
1099                 // This path cannot occur. `static mut X` is not checked
1100                 // for aliasability violations.
1101                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1102             }
1103             mc::AliasableStatic | mc::AliasableBorrowed => {}
1104         };
1105         let blame = cmt.immutability_blame();
1106         let mut err = match blame {
1107             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1108                 // FIXME: the distinction between these 2 messages looks wrong.
1109                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1110                     // The aliasability violation with closure captures can
1111                     // happen for nested closures, so we know the enclosing
1112                     // closure incorrectly accepts an `Fn` while it needs to
1113                     // be `FnMut`.
1114                     "consider changing this to accept closures that implement `FnMut`"
1115
1116                 } else {
1117                     "consider changing this closure to take self by mutable reference"
1118                 };
1119                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(id);
1120                 let help_span = self.tcx.hir().span_by_hir_id(hir_id);
1121                 self.cannot_act_on_capture_in_sharable_fn(span,
1122                                                           prefix,
1123                                                           (help_span, help_msg),
1124                                                           Origin::Ast)
1125             }
1126             _ =>  {
1127                 self.cannot_assign_into_immutable_reference(span, prefix,
1128                                                             Origin::Ast)
1129             }
1130         };
1131         self.note_immutability_blame(
1132             &mut err,
1133             blame,
1134             cmt.hir_id
1135         );
1136
1137         if is_closure {
1138             err.help("closures behind references must be called via `&mut`");
1139         }
1140         err.emit();
1141         self.signal_error();
1142     }
1143
1144     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1145     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1146         // Check whether the argument is an immutable reference
1147         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1148         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1149             mutbl: hir::Mutability::MutImmutable,
1150             ref ty
1151         }) = pty.node {
1152             // Account for existing lifetimes when generating the message
1153             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1154                 Ok(snippet) => snippet,
1155                 _ => return None
1156             };
1157
1158             let lifetime_snippet = if !lifetime.is_elided() {
1159                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1160                     Ok(lifetime_snippet) => lifetime_snippet,
1161                     _ => return None
1162                 })
1163             } else {
1164                 String::new()
1165             };
1166             Some(format!("use `&{}mut {}` here to make mutable",
1167                          lifetime_snippet,
1168                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1169         } else {
1170             None
1171         }
1172     }
1173
1174     fn local_binding_mode(&self, hir_id: hir::HirId) -> ty::BindingMode {
1175         let pat = match self.tcx.hir().get_by_hir_id(hir_id) {
1176             Node::Binding(pat) => pat,
1177             node => bug!("bad node for local: {:?}", node)
1178         };
1179
1180         match pat.node {
1181             hir::PatKind::Binding(..) => {
1182                 *self.tables
1183                      .pat_binding_modes()
1184                      .get(pat.hir_id)
1185                      .expect("missing binding mode")
1186             }
1187             _ => bug!("local is not a binding: {:?}", pat)
1188         }
1189     }
1190
1191     fn local_ty(&self, hir_id: hir::HirId) -> (Option<&hir::Ty>, bool) {
1192         let parent = self.tcx.hir().get_parent_node_by_hir_id(hir_id);
1193         let parent_node = self.tcx.hir().get_by_hir_id(parent);
1194
1195         // The parent node is like a fn
1196         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1197             // `nid`'s parent's `Body`
1198             let fn_body = self.tcx.hir().body(fn_like.body());
1199             // Get the position of `node_id` in the arguments list
1200             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.hir_id == hir_id);
1201             if let Some(i) = arg_pos {
1202                 // The argument's `Ty`
1203                 (Some(&fn_like.decl().inputs[i]),
1204                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1205             } else {
1206                 (None, false)
1207             }
1208         } else {
1209             (None, false)
1210         }
1211     }
1212
1213     fn note_immutability_blame(&self,
1214                                db: &mut DiagnosticBuilder<'_>,
1215                                blame: Option<ImmutabilityBlame<'_>>,
1216                                error_hir_id: hir::HirId) {
1217         match blame {
1218             None => {}
1219             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1220             Some(ImmutabilityBlame::ImmLocal(hir_id)) => {
1221                 self.note_immutable_local(db, error_hir_id, hir_id)
1222             }
1223             Some(ImmutabilityBlame::LocalDeref(hir_id)) => {
1224                 match self.local_binding_mode(hir_id) {
1225                     ty::BindByReference(..) => {
1226                         let let_span = self.tcx.hir().span_by_hir_id(hir_id);
1227                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1228                         if let Some(replace_str) = suggestion {
1229                             db.span_suggestion(
1230                                 let_span,
1231                                 "use a mutable reference instead",
1232                                 replace_str,
1233                                 // I believe this can be machine applicable,
1234                                 // but if there are multiple attempted uses of an immutable
1235                                 // reference, I don't know how rustfix handles it, it might
1236                                 // attempt fixing them multiple times.
1237                                 //                              @estebank
1238                                 Applicability::Unspecified,
1239                             );
1240                         }
1241                     }
1242                     ty::BindByValue(..) => {
1243                         if let (Some(local_ty), is_implicit_self) = self.local_ty(hir_id) {
1244                             if let Some(msg) =
1245                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1246                                 db.span_label(local_ty.span, msg);
1247                             }
1248                         }
1249                     }
1250                 }
1251             }
1252             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1253                 let hir_id = match self.tcx.hir().as_local_hir_id(field.did) {
1254                     Some(hir_id) => hir_id,
1255                     None => return
1256                 };
1257
1258                 if let Node::Field(ref field) = self.tcx.hir().get_by_hir_id(hir_id) {
1259                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1260                         db.span_label(field.ty.span, msg);
1261                     }
1262                 }
1263             }
1264         }
1265     }
1266
1267      // Suggest a fix when trying to mutably borrow an immutable local
1268      // binding: either to make the binding mutable (if its type is
1269      // not a mutable reference) or to avoid borrowing altogether
1270     fn note_immutable_local(&self,
1271                             db: &mut DiagnosticBuilder<'_>,
1272                             borrowed_hir_id: hir::HirId,
1273                             binding_hir_id: hir::HirId) {
1274         let let_span = self.tcx.hir().span_by_hir_id(binding_hir_id);
1275         if let ty::BindByValue(..) = self.local_binding_mode(binding_hir_id) {
1276             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1277                 let (ty, is_implicit_self) = self.local_ty(binding_hir_id);
1278                 if is_implicit_self && snippet != "self" {
1279                     // avoid suggesting `mut &self`.
1280                     return
1281                 }
1282                 if let Some(&hir::TyKind::Rptr(
1283                     _,
1284                     hir::MutTy {
1285                         mutbl: hir::MutMutable,
1286                         ..
1287                     },
1288                 )) = ty.map(|t| &t.node)
1289                 {
1290                     let borrow_expr_id = self.tcx.hir().get_parent_node_by_hir_id(borrowed_hir_id);
1291                     db.span_suggestion(
1292                         self.tcx.hir().span_by_hir_id(borrow_expr_id),
1293                         "consider removing the `&mut`, as it is an \
1294                         immutable binding to a mutable reference",
1295                         snippet,
1296                         Applicability::MachineApplicable,
1297                     );
1298                 } else {
1299                     db.span_suggestion(
1300                         let_span,
1301                         "make this binding mutable",
1302                         format!("mut {}", snippet),
1303                         Applicability::MachineApplicable,
1304                     );
1305                 }
1306             }
1307         }
1308     }
1309
1310     fn report_out_of_scope_escaping_closure_capture(&self,
1311                                                     err: &BckError<'a, 'tcx>,
1312                                                     capture_span: Span)
1313     {
1314         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1315
1316         let suggestion =
1317             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1318                 Ok(string) => format!("move {}", string),
1319                 Err(_) => "move |<args>| <body>".to_string()
1320             };
1321
1322         self.cannot_capture_in_long_lived_closure(err.span,
1323                                                   &cmt_path_or_string,
1324                                                   capture_span,
1325                                                   Origin::Ast)
1326             .span_suggestion(
1327                  err.span,
1328                  &format!("to force the closure to take ownership of {} \
1329                            (and any other referenced variables), \
1330                            use the `move` keyword",
1331                            cmt_path_or_string),
1332                  suggestion,
1333                  Applicability::MachineApplicable,
1334             )
1335             .emit();
1336         self.signal_error();
1337     }
1338
1339     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1340         match *region {
1341             ty::ReScope(scope) => {
1342                 Some(self.tcx.sess.source_map().end_point(
1343                         scope.span(self.tcx, &self.region_scope_tree)))
1344             }
1345             _ => None
1346         }
1347     }
1348
1349     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder<'_>, err: &BckError<'a, 'tcx>,
1350                                     error_span: &Span) {
1351         match err.cmt.note {
1352             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1353                 // If this is an `Fn` closure, it simply can't mutate upvars.
1354                 // If it's an `FnMut` closure, the original variable was declared immutable.
1355                 // We need to determine which is the case here.
1356                 let kind = match err.cmt.upvar_cat().unwrap() {
1357                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1358                     _ => bug!()
1359                 };
1360                 if *kind == ty::ClosureKind::Fn {
1361                     let closure_hir_id =
1362                         self.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id);
1363                     db.span_help(self.tcx.hir().span_by_hir_id(closure_hir_id),
1364                                  "consider changing this closure to take \
1365                                   self by mutable reference");
1366                 }
1367             }
1368             _ => {
1369                 if let Categorization::Deref(..) = err.cmt.cat {
1370                     db.span_label(*error_span, "cannot borrow as mutable");
1371                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1372                     let span = self.tcx.hir().span_by_hir_id(local_id);
1373                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1374                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1375                             db.span_label(*error_span, "cannot reborrow mutably");
1376                             db.span_label(*error_span, "try removing `&mut` here");
1377                         } else {
1378                             db.span_label(*error_span, "cannot borrow mutably");
1379                         }
1380                     } else {
1381                         db.span_label(*error_span, "cannot borrow mutably");
1382                     }
1383                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1384                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1385                         db.span_label(*error_span,
1386                                       "cannot mutably borrow field of immutable binding");
1387                     }
1388                 }
1389             }
1390         }
1391     }
1392     pub fn append_loan_path_to_string(&self,
1393                                       loan_path: &LoanPath<'tcx>,
1394                                       out: &mut String) {
1395         match loan_path.kind {
1396             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id }, closure_expr_id: _ }) => {
1397                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1398             }
1399             LpVar(id) => {
1400                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1401             }
1402
1403             LpDowncast(ref lp_base, variant_def_id) => {
1404                 out.push('(');
1405                 self.append_loan_path_to_string(&lp_base, out);
1406                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1407                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1408                 out.push(')');
1409             }
1410
1411             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1412                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1413                 out.push('.');
1414                 out.push_str(&info.as_str());
1415             }
1416
1417             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1418                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1419                 out.push_str("[..]");
1420             }
1421
1422             LpExtend(ref lp_base, _, LpDeref(_)) => {
1423                 out.push('*');
1424                 self.append_loan_path_to_string(&lp_base, out);
1425             }
1426         }
1427     }
1428
1429     pub fn append_autoderefd_loan_path_to_string(&self,
1430                                                  loan_path: &LoanPath<'tcx>,
1431                                                  out: &mut String) {
1432         match loan_path.kind {
1433             LpExtend(ref lp_base, _, LpDeref(_)) => {
1434                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1435                 // rules would normally allow users to omit the `*x`.
1436                 // So just serialize such paths to `x.f` or x[3]` respectively.
1437                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1438             }
1439
1440             LpDowncast(ref lp_base, variant_def_id) => {
1441                 out.push('(');
1442                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1443                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1444                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1445                 out.push(')');
1446             }
1447
1448             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1449                 self.append_loan_path_to_string(loan_path, out)
1450             }
1451         }
1452     }
1453
1454     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1455         let mut result = String::new();
1456         self.append_loan_path_to_string(loan_path, &mut result);
1457         result
1458     }
1459
1460     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1461         cmt.descriptive_string(self.tcx)
1462     }
1463
1464     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1465         match opt_loan_path(cmt) {
1466             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1467             None => self.cmt_to_cow_str(cmt).into_owned(),
1468         }
1469     }
1470 }
1471
1472 impl BitwiseOperator for LoanDataFlowOperator {
1473     #[inline]
1474     fn join(&self, succ: usize, pred: usize) -> usize {
1475         succ | pred // loans from both preds are in scope
1476     }
1477 }
1478
1479 impl DataFlowOperator for LoanDataFlowOperator {
1480     #[inline]
1481     fn initial_value(&self) -> bool {
1482         false // no loans in scope by default
1483     }
1484 }
1485
1486 impl<'tcx> fmt::Debug for InteriorKind {
1487     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1488         match *self {
1489             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1490             InteriorElement => write!(f, "[]"),
1491         }
1492     }
1493 }
1494
1495 impl<'tcx> fmt::Debug for Loan<'tcx> {
1496     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1497         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1498                self.index,
1499                self.loan_path,
1500                self.kind,
1501                self.gen_scope,
1502                self.kill_scope,
1503                self.restricted_paths)
1504     }
1505 }
1506
1507 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1508     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1509         match self.kind {
1510             LpVar(id) => {
1511                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_string(id)))
1512             }
1513
1514             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1515                 let s = ty::tls::with(|tcx| {
1516                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1517                     tcx.hir().node_to_string(var_node_id)
1518                 });
1519                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1520             }
1521
1522             LpDowncast(ref lp, variant_def_id) => {
1523                 let variant_str = if variant_def_id.is_local() {
1524                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1525                 } else {
1526                     format!("{:?}", variant_def_id)
1527                 };
1528                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1529             }
1530
1531             LpExtend(ref lp, _, LpDeref(_)) => {
1532                 write!(f, "{:?}.*", lp)
1533             }
1534
1535             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1536                 write!(f, "{:?}.{:?}", lp, interior)
1537             }
1538         }
1539     }
1540 }
1541
1542 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1543     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1544         match self.kind {
1545             LpVar(id) => {
1546                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_user_string(id)))
1547             }
1548
1549             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1550                 let s = ty::tls::with(|tcx| {
1551                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1552                     tcx.hir().node_to_string(var_node_id)
1553                 });
1554                 write!(f, "$({} captured by closure)", s)
1555             }
1556
1557             LpDowncast(ref lp, variant_def_id) => {
1558                 let variant_str = if variant_def_id.is_local() {
1559                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1560                 } else {
1561                     format!("{:?}", variant_def_id)
1562                 };
1563                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1564             }
1565
1566             LpExtend(ref lp, _, LpDeref(_)) => {
1567                 write!(f, "{}.*", lp)
1568             }
1569
1570             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1571                 write!(f, "{}.{:?}", lp, interior)
1572             }
1573         }
1574     }
1575 }