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::ast;
  38 use syntax_pos::{MultiSpan, Span};
  39 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
  40 use log::debug;
  41
  42 use rustc::hir;
  43
  44 use crate::dataflow::{DataFlowContext, BitwiseOperator, DataFlowOperator, KillFrom};
  45
  46 pub mod check_loans;
  47
  48 pub mod gather_loans;
  49
  50 pub mod move_data;
  51
  52 mod unused;
  53
  54 #[derive(Clone, Copy)]
  55 pub struct LoanDataFlowOperator;
  56
  57 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  58
  59 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  60     tcx.par_body_owners(|body_owner_def_id| {
  61         tcx.ensure().borrowck(body_owner_def_id);
  62     });
  63 }
  64
  65 pub fn provide(providers: &mut Providers<'_>) {
  66     *providers = Providers {
  67         borrowck,
  68         ..*providers
  69     };
  70 }
  71
  72 /// Collection of conclusions determined via borrow checker analyses.
  73 pub struct AnalysisData<'a, 'tcx: 'a> {
  74     pub all_loans: Vec<Loan<'tcx>>,
  75     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  76     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  77 }
  78
  79 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  80     -> Lrc<BorrowCheckResult>
  81 {
  82     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  83
  84     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  85
  86     let owner_id = tcx.hir().as_local_hir_id(owner_def_id).unwrap();
  87
  88     match tcx.hir().get_by_hir_id(owner_id) {
  89         Node::StructCtor(_) |
  90         Node::Variant(_) => {
  91             // We get invoked with anything that has MIR, but some of
  92             // those things (notably the synthesized constructors from
  93             // tuple structs/variants) do not have an associated body
  94             // and do not need borrowchecking.
  95             return Lrc::new(BorrowCheckResult {
  96                 used_mut_nodes: Default::default(),
  97                 signalled_any_error: SignalledError::NoErrorsSeen,
  98             })
  99         }
 100         _ => { }
 101     }
 102
 103     let body_id = tcx.hir().body_owned_by(owner_id);
 104     let tables = tcx.typeck_tables_of(owner_def_id);
 105     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 106     let body = tcx.hir().body(body_id);
 107     let mut bccx = BorrowckCtxt {
 108         tcx,
 109         tables,
 110         region_scope_tree,
 111         owner_def_id,
 112         body,
 113         used_mut_nodes: Default::default(),
 114         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 115     };
 116
 117     // Eventually, borrowck will always read the MIR, but at the
 118     // moment we do not. So, for now, we always force MIR to be
 119     // constructed for a given fn, since this may result in errors
 120     // being reported and we want that to happen.
 121     //
 122     // Note that `mir_validated` is a "stealable" result; the
 123     // thief, `optimized_mir()`, forces borrowck, so we know that
 124     // is not yet stolen.
 125     tcx.ensure().mir_validated(owner_def_id);
 126
 127     // option dance because you can't capture an uninitialized variable
 128     // by mut-ref.
 129     let mut cfg = None;
 130     if let Some(AnalysisData { all_loans,
 131                                loans: loan_dfcx,
 132                                move_data: flowed_moves }) =
 133         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 134                                      |bccx| {
 135                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 136                                          cfg.as_mut().unwrap()
 137                                      })
 138     {
 139         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 140     }
 141
 142     if !tcx.use_mir_borrowck() {
 143         unused::check(&mut bccx, body);
 144     }
 145
 146     Lrc::new(BorrowCheckResult {
 147         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 148         signalled_any_error: bccx.signalled_any_error.into_inner(),
 149     })
 150 }
 151
 152 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 153                                                  force_analysis: bool,
 154                                                  body_id: hir::BodyId,
 155                                                  get_cfg: F)
 156                                                  -> Option<AnalysisData<'a, 'tcx>>
 157     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 158 {
 159     // Check the body of fn items.
 160     let (all_loans, move_data) =
 161         gather_loans::gather_loans_in_fn(this, body_id);
 162
 163     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 164         // large arrays of data inserted as constants can take a lot of
 165         // time and memory to borrow-check - see issue #36799. However,
 166         // they don't have places, so no borrow-check is actually needed.
 167         // Recognize that case and skip borrow-checking.
 168         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 169         return None;
 170     } else {
 171         debug!("propagating loans in {:?}", body_id);
 172     }
 173
 174     let cfg = get_cfg(this);
 175     let mut loan_dfcx =
 176         DataFlowContext::new(this.tcx,
 177                              "borrowck",
 178                              Some(this.body),
 179                              cfg,
 180                              LoanDataFlowOperator,
 181                              all_loans.len());
 182     for (loan_idx, loan) in all_loans.iter().enumerate() {
 183         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 184         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 185                            loan.kill_scope.item_local_id(),
 186                            loan_idx);
 187     }
 188     loan_dfcx.add_kills_from_flow_exits(cfg);
 189     loan_dfcx.propagate(cfg, this.body);
 190
 191     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 192                                                       this,
 193                                                       cfg,
 194                                                       this.body);
 195
 196     Some(AnalysisData { all_loans,
 197                         loans: loan_dfcx,
 198                         move_data:flowed_moves })
 199 }
 200
 201 /// Accessor for introspective clients inspecting `AnalysisData` and
 202 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 203 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 204     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 205     body_id: hir::BodyId,
 206     cfg: &cfg::CFG)
 207     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 208 {
 209     let owner_id = tcx.hir().body_owner(body_id);
 210     let owner_def_id = tcx.hir().local_def_id(owner_id);
 211     let tables = tcx.typeck_tables_of(owner_def_id);
 212     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 213     let body = tcx.hir().body(body_id);
 214     let mut bccx = BorrowckCtxt {
 215         tcx,
 216         tables,
 217         region_scope_tree,
 218         owner_def_id,
 219         body,
 220         used_mut_nodes: Default::default(),
 221         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 222     };
 223
 224     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 225     (bccx, dataflow_data.unwrap())
 226 }
 227
 228 // ----------------------------------------------------------------------
 229 // Type definitions
 230
 231 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 232     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 233
 234     // tables for the current thing we are checking; set to
 235     // Some in `borrowck_fn` and cleared later
 236     tables: &'a ty::TypeckTables<'tcx>,
 237
 238     region_scope_tree: Lrc<region::ScopeTree>,
 239
 240     owner_def_id: DefId,
 241
 242     body: &'tcx hir::Body,
 243
 244     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 245
 246     signalled_any_error: Cell<SignalledError>,
 247 }
 248
 249
 250 impl<'a, 'tcx: 'a> BorrowckCtxt<'a, 'tcx> {
 251     fn signal_error(&self) {
 252         self.signalled_any_error.set(SignalledError::SawSomeError);
 253     }
 254 }
 255
 256 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 257     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 258                                                      sp: S,
 259                                                      msg: &str,
 260                                                      code: DiagnosticId)
 261                                                      -> DiagnosticBuilder<'a>
 262     {
 263         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 264     }
 265
 266     fn struct_span_err<S: Into<MultiSpan>>(self,
 267                                            sp: S,
 268                                            msg: &str)
 269                                            -> DiagnosticBuilder<'a>
 270     {
 271         self.tcx.sess.struct_span_err(sp, msg)
 272     }
 273
 274     fn cancel_if_wrong_origin(self,
 275                               mut diag: DiagnosticBuilder<'a>,
 276                               o: Origin)
 277                               -> DiagnosticBuilder<'a>
 278     {
 279         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 280             self.tcx.sess.diagnostic().cancel(&mut diag);
 281         }
 282         diag
 283     }
 284 }
 285
 286 ///////////////////////////////////////////////////////////////////////////
 287 // Loans and loan paths
 288
 289 /// Record of a loan that was issued.
 290 pub struct Loan<'tcx> {
 291     index: usize,
 292     loan_path: Rc<LoanPath<'tcx>>,
 293     kind: ty::BorrowKind,
 294     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 295
 296     /// gen_scope indicates where loan is introduced. Typically the
 297     /// loan is introduced at the point of the borrow, but in some
 298     /// cases, notably method arguments, the loan may be introduced
 299     /// only later, once it comes into scope. See also
 300     /// `GatherLoanCtxt::compute_gen_scope`.
 301     gen_scope: region::Scope,
 302
 303     /// kill_scope indicates when the loan goes out of scope. This is
 304     /// either when the lifetime expires or when the local variable
 305     /// which roots the loan-path goes out of scope, whichever happens
 306     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 307     kill_scope: region::Scope,
 308     span: Span,
 309     cause: euv::LoanCause,
 310 }
 311
 312 impl<'tcx> Loan<'tcx> {
 313     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 314         self.loan_path.clone()
 315     }
 316 }
 317
 318 #[derive(Eq)]
 319 pub struct LoanPath<'tcx> {
 320     kind: LoanPathKind<'tcx>,
 321     ty: Ty<'tcx>,
 322 }
 323
 324 impl<'tcx> PartialEq for LoanPath<'tcx> {
 325     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 326         self.kind == that.kind
 327     }
 328 }
 329
 330 impl<'tcx> Hash for LoanPath<'tcx> {
 331     fn hash<H: Hasher>(&self, state: &mut H) {
 332         self.kind.hash(state);
 333     }
 334 }
 335
 336 #[derive(PartialEq, Eq, Hash, Debug)]
 337 pub enum LoanPathKind<'tcx> {
 338     LpVar(hir::HirId),                          // `x` in README.md
 339     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 340     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 341     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 342 }
 343
 344 impl<'tcx> LoanPath<'tcx> {
 345     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 346         LoanPath { kind: kind, ty: ty }
 347     }
 348
 349     fn to_type(&self) -> Ty<'tcx> { self.ty }
 350
 351     fn has_downcast(&self) -> bool {
 352         match self.kind {
 353             LpDowncast(_, _) => true,
 354             LpExtend(ref lp, _, LpInterior(_, _)) => {
 355                 lp.has_downcast()
 356             }
 357             _ => false,
 358         }
 359     }
 360 }
 361
 362 // FIXME (pnkfelix): See discussion here
 363 // https://github.com/pnkfelix/rust/commit/
 364 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 365 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 366
 367 // A local, "cleaned" version of `mc::InteriorKind` that drops
 368 // information that is not relevant to loan-path analysis. (In
 369 // particular, the distinction between how precisely an array-element
 370 // is tracked is irrelevant here.)
 371 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 372 pub enum InteriorKind {
 373     InteriorField(mc::FieldIndex),
 374     InteriorElement,
 375 }
 376
 377 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 378 impl ToInteriorKind for mc::InteriorKind {
 379     fn cleaned(self) -> InteriorKind {
 380         match self {
 381             mc::InteriorField(name) => InteriorField(name),
 382             mc::InteriorElement(_) => InteriorElement,
 383         }
 384     }
 385 }
 386
 387 // This can be:
 388 // - a pointer dereference (`*P` in README.md)
 389 // - a field reference, with an optional definition of the containing
 390 //   enum variant (`P.f` in README.md)
 391 // `DefId` is present when the field is part of struct that is in
 392 // a variant of an enum. For instance in:
 393 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 394 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 395 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 396 pub enum LoanPathElem<'tcx> {
 397     LpDeref(mc::PointerKind<'tcx>),
 398     LpInterior(Option<DefId>, InteriorKind),
 399 }
 400
 401 fn closure_to_block(closure_id: LocalDefId,
 402                     tcx: TyCtxt<'_, '_, '_>) -> ast::NodeId {
 403     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 404     match tcx.hir().get(closure_id) {
 405         Node::Expr(expr) => match expr.node {
 406             hir::ExprKind::Closure(.., body_id, _, _) => {
 407                 tcx.hir().hir_to_node_id(body_id.hir_id)
 408             }
 409             _ => {
 410                 bug!("encountered non-closure id: {}", closure_id)
 411             }
 412         },
 413         _ => bug!("encountered non-expr id: {}", closure_id)
 414     }
 415 }
 416
 417 impl<'a, 'tcx> LoanPath<'tcx> {
 418     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 419         match self.kind {
 420             LpVar(hir_id) => {
 421                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 422             }
 423             LpUpvar(upvar_id) => {
 424                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 425                 let hir_id = bccx.tcx.hir().node_to_hir_id(block_id);
 426                 region::Scope { id: hir_id.local_id, data: region::ScopeData::Node }
 427             }
 428             LpDowncast(ref base, _) |
 429             LpExtend(ref base, ..) => base.kill_scope(bccx),
 430         }
 431     }
 432
 433     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 434         match (&self.kind, &other.kind) {
 435             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 436              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 437                 if id == id2 && opt_variant_id == opt_variant_id2 {
 438                     base.has_fork(&base2)
 439                 } else {
 440                     true
 441                 },
 442             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 443             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 444             _ => false,
 445         }
 446     }
 447
 448     fn depth(&self) -> usize {
 449         match self.kind {
 450             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 451             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 452             _ => 0,
 453         }
 454     }
 455
 456     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 457         match (&self.kind, &other.kind) {
 458             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 459              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 460                 if id == id2 && opt_variant_id == opt_variant_id2 {
 461                     base.common(&base2).map(|x| {
 462                         let xd = x.depth();
 463                         if base.depth() == xd && base2.depth() == xd {
 464                             LoanPath {
 465                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 466                                 ty: self.ty,
 467                             }
 468                         } else {
 469                             x
 470                         }
 471                     })
 472                 } else {
 473                     base.common(&base2)
 474                 }
 475             }
 476             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 477             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 478             (&LpVar(id), &LpVar(id2)) => {
 479                 if id == id2 {
 480                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 481                 } else {
 482                     None
 483                 }
 484             }
 485             (&LpUpvar(id), &LpUpvar(id2)) => {
 486                 if id == id2 {
 487                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 488                 } else {
 489                     None
 490                 }
 491             }
 492             _ => None,
 493         }
 494     }
 495 }
 496
 497 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 498 // mutable independently of the struct it belongs to. (#35937)
 499 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 500     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 501
 502     match cmt.cat {
 503         Categorization::Rvalue(..) |
 504         Categorization::ThreadLocal(..) |
 505         Categorization::StaticItem => {
 506             (None, false)
 507         }
 508
 509         Categorization::Local(id) => {
 510             (Some(new_lp(LpVar(id))), false)
 511         }
 512
 513         Categorization::Upvar(mc::Upvar { id, .. }) => {
 514             (Some(new_lp(LpUpvar(id))), false)
 515         }
 516
 517         Categorization::Deref(ref cmt_base, pk) => {
 518             let lp = opt_loan_path_is_field(cmt_base);
 519             (lp.0.map(|lp| {
 520                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 521             }), lp.1)
 522         }
 523
 524         Categorization::Interior(ref cmt_base, ik) => {
 525             (opt_loan_path(cmt_base).map(|lp| {
 526                 let opt_variant_id = match cmt_base.cat {
 527                     Categorization::Downcast(_, did) =>  Some(did),
 528                     _ => None
 529                 };
 530                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 531             }), true)
 532         }
 533
 534         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 535             let lp = opt_loan_path_is_field(cmt_base);
 536             (lp.0.map(|lp| {
 537                 new_lp(LpDowncast(lp, variant_def_id))
 538             }), lp.1)
 539         }
 540     }
 541 }
 542
 543 /// Computes the `LoanPath` (if any) for a `cmt`.
 544 /// Note that this logic is somewhat duplicated in
 545 /// the method `compute()` found in `gather_loans::restrictions`,
 546 /// which allows it to share common loan path pieces as it
 547 /// traverses the CMT.
 548 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 549     opt_loan_path_is_field(cmt).0
 550 }
 551
 552 ///////////////////////////////////////////////////////////////////////////
 553 // Errors
 554
 555 // Errors that can occur
 556 #[derive(Debug, PartialEq)]
 557 pub enum bckerr_code<'tcx> {
 558     err_mutbl,
 559     /// superscope, subscope, loan cause
 560     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 561     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 562 }
 563
 564 // Combination of an error code and the categorization of the expression
 565 // that caused it
 566 #[derive(Debug, PartialEq)]
 567 pub struct BckError<'c, 'tcx: 'c> {
 568     span: Span,
 569     cause: AliasableViolationKind,
 570     cmt: &'c mc::cmt_<'tcx>,
 571     code: bckerr_code<'tcx>
 572 }
 573
 574 #[derive(Copy, Clone, Debug, PartialEq)]
 575 pub enum AliasableViolationKind {
 576     MutabilityViolation,
 577     BorrowViolation(euv::LoanCause)
 578 }
 579
 580 #[derive(Copy, Clone, Debug)]
 581 pub enum MovedValueUseKind {
 582     MovedInUse,
 583     MovedInCapture,
 584 }
 585
 586 ///////////////////////////////////////////////////////////////////////////
 587 // Misc
 588
 589 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 590     pub fn is_subregion_of(&self,
 591                            r_sub: ty::Region<'tcx>,
 592                            r_sup: ty::Region<'tcx>)
 593                            -> bool
 594     {
 595         let region_rels = RegionRelations::new(self.tcx,
 596                                                self.owner_def_id,
 597                                                &self.region_scope_tree,
 598                                                &self.tables.free_region_map);
 599         region_rels.is_subregion_of(r_sub, r_sup)
 600     }
 601
 602     pub fn report(&self, err: BckError<'a, 'tcx>) {
 603         // Catch and handle some particular cases.
 604         match (&err.code, &err.cause) {
 605             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 606              &BorrowViolation(euv::ClosureCapture(span))) |
 607             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 608              &BorrowViolation(euv::ClosureCapture(span))) |
 609             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 610              &BorrowViolation(euv::ClosureCapture(span))) => {
 611                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 612             }
 613             _ => { }
 614         }
 615
 616         self.report_bckerr(&err);
 617     }
 618
 619     pub fn report_use_of_moved_value(&self,
 620                                      use_span: Span,
 621                                      use_kind: MovedValueUseKind,
 622                                      lp: &LoanPath<'tcx>,
 623                                      the_move: &move_data::Move,
 624                                      moved_lp: &LoanPath<'tcx>) {
 625         let (verb, verb_participle) = match use_kind {
 626             MovedInUse => ("use", "used"),
 627             MovedInCapture => ("capture", "captured"),
 628         };
 629
 630         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 631             move_data::Declared => {
 632                 // If this is an uninitialized variable, just emit a simple warning
 633                 // and return.
 634                 self.cannot_act_on_uninitialized_variable(use_span,
 635                                                           verb,
 636                                                           &self.loan_path_to_string(lp),
 637                                                           Origin::Ast)
 638                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 639                                                   self.loan_path_to_string(lp)))
 640                     .emit();
 641                 self.signal_error();
 642                 return;
 643             }
 644             _ => {
 645                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 646                 // normally generate a rather confusing message:
 647                 //
 648                 //     error: use of moved value: `x.b`
 649                 //     note: `x.a` moved here...
 650                 //
 651                 // What we want to do instead is get the 'common ancestor' of the two moves and
 652                 // use that for most of the message instead, giving is something like this:
 653                 //
 654                 //     error: use of moved value: `x`
 655                 //     note: `x` moved here (through moving `x.a`)...
 656
 657                 let common = moved_lp.common(lp);
 658                 let has_common = common.is_some();
 659                 let has_fork = moved_lp.has_fork(lp);
 660                 let (nl, ol, moved_lp_msg) =
 661                     if has_fork && has_common {
 662                         let nl = self.loan_path_to_string(&common.unwrap());
 663                         let ol = nl.clone();
 664                         let moved_lp_msg = format!(" (through moving `{}`)",
 665                                                    self.loan_path_to_string(moved_lp));
 666                         (nl, ol, moved_lp_msg)
 667                     } else {
 668                         (self.loan_path_to_string(lp),
 669                          self.loan_path_to_string(moved_lp),
 670                          String::new())
 671                     };
 672
 673                 let partial = moved_lp.depth() > lp.depth();
 674                 let msg = if !has_fork && partial { "partially " }
 675                           else if has_fork && !has_common { "collaterally "}
 676                 else { "" };
 677                 let mut err = self.cannot_act_on_moved_value(use_span,
 678                                                              verb,
 679                                                              msg,
 680                                                              Some(nl),
 681                                                              Origin::Ast);
 682                 let need_note = match lp.ty.sty {
 683                     ty::Closure(id, _) => {
 684                         let hir_id = self.tcx.hir().as_local_hir_id(id).unwrap();
 685                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 686                             err.span_note(*span, &format!(
 687                                 "closure cannot be invoked more than once because \
 688                                 it moves the variable `{}` out of its environment",
 689                                 name
 690                             ));
 691                             false
 692                         } else {
 693                             true
 694                         }
 695                     }
 696                     _ => true,
 697                 };
 698                 (ol, moved_lp_msg, err, need_note)
 699             }
 700         };
 701
 702         // Get type of value and span where it was previously
 703         // moved.
 704         let hir_id = hir::HirId {
 705             owner: self.body.value.hir_id.owner,
 706             local_id: the_move.id
 707         };
 708         let (move_span, move_note) = match the_move.kind {
 709             move_data::Declared => {
 710                 unreachable!();
 711             }
 712
 713             move_data::MoveExpr |
 714             move_data::MovePat => (self.tcx.hir().span_by_hir_id(hir_id), ""),
 715
 716             move_data::Captured =>
 717                 (match self.tcx.hir().expect_expr_by_hir_id(hir_id).node {
 718                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 719                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 720                                   the_move.id, r),
 721                 }, " (into closure)"),
 722         };
 723
 724         // Annotate the use and the move in the span. Watch out for
 725         // the case where the use and the move are the same. This
 726         // means the use is in a loop.
 727         err = if use_span == move_span {
 728             err.span_label(
 729                 use_span,
 730                 format!("value moved{} here in previous iteration of loop",
 731                          move_note));
 732             err
 733         } else {
 734             err.span_label(use_span, format!("value {} here after move", verb_participle));
 735             err.span_label(move_span, format!("value moved{} here", move_note));
 736             err
 737         };
 738
 739         if need_note {
 740             err.note(&format!(
 741                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 742                 if moved_lp.has_downcast() {
 743                     "the value".to_string()
 744                 } else {
 745                     format!("`{}`", self.loan_path_to_string(moved_lp))
 746                 },
 747                 moved_lp.ty));
 748         }
 749
 750         // Note: we used to suggest adding a `ref binding` or calling
 751         // `clone` but those suggestions have been removed because
 752         // they are often not what you actually want to do, and were
 753         // not considered particularly helpful.
 754
 755         err.emit();
 756         self.signal_error();
 757     }
 758
 759     pub fn report_partial_reinitialization_of_uninitialized_structure(
 760             &self,
 761             span: Span,
 762             lp: &LoanPath<'tcx>) {
 763         self.cannot_partially_reinit_an_uninit_struct(span,
 764                                                       &self.loan_path_to_string(lp),
 765                                                       Origin::Ast)
 766             .emit();
 767         self.signal_error();
 768     }
 769
 770     pub fn report_reassigned_immutable_variable(&self,
 771                                                 span: Span,
 772                                                 lp: &LoanPath<'tcx>,
 773                                                 assign:
 774                                                 &move_data::Assignment) {
 775         let mut err = self.cannot_reassign_immutable(span,
 776                                                      &self.loan_path_to_string(lp),
 777                                                      false,
 778                                                      Origin::Ast);
 779         err.span_label(span, "cannot assign twice to immutable variable");
 780         if span != assign.span {
 781             err.span_label(assign.span, format!("first assignment to `{}`",
 782                                                 self.loan_path_to_string(lp)));
 783         }
 784         err.emit();
 785         self.signal_error();
 786     }
 787
 788     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 789         let error_span = err.span.clone();
 790
 791         match err.code {
 792             err_mutbl => {
 793                 let descr: Cow<'static, str> = match err.cmt.note {
 794                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 795                         self.cmt_to_cow_str(&err.cmt)
 796                     }
 797                     _ => match opt_loan_path_is_field(&err.cmt) {
 798                         (None, true) => {
 799                             format!("{} of {} binding",
 800                                     self.cmt_to_cow_str(&err.cmt),
 801                                     err.cmt.mutbl.to_user_str()).into()
 802
 803                         }
 804                         (None, false) => {
 805                             format!("{} {}",
 806                                     err.cmt.mutbl.to_user_str(),
 807                                     self.cmt_to_cow_str(&err.cmt)).into()
 808
 809                         }
 810                         (Some(lp), true) => {
 811                             format!("{} `{}` of {} binding",
 812                                     self.cmt_to_cow_str(&err.cmt),
 813                                     self.loan_path_to_string(&lp),
 814                                     err.cmt.mutbl.to_user_str()).into()
 815                         }
 816                         (Some(lp), false) => {
 817                             format!("{} {} `{}`",
 818                                     err.cmt.mutbl.to_user_str(),
 819                                     self.cmt_to_cow_str(&err.cmt),
 820                                     self.loan_path_to_string(&lp)).into()
 821                         }
 822                     }
 823                 };
 824
 825                 let mut db = match err.cause {
 826                     MutabilityViolation => {
 827                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 828                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 829                             let hir_id = upvar_id.var_path.hir_id;
 830                             let sp = self.tcx.hir().span_by_hir_id(hir_id);
 831                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 832                                                   environment for modifications";
 833                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 834                                 (_, &Categorization::Upvar(mc::Upvar {
 835                                     kind: ty::ClosureKind::Fn, ..
 836                                 })) => {
 837                                     db.note(fn_closure_msg);
 838                                     // we should point at the cause for this closure being
 839                                     // identified as `Fn` (like in signature of method this
 840                                     // closure was passed into)
 841                                 }
 842                                 (Ok(ref snippet), ref cat) => {
 843                                     let msg = &format!("consider making `{}` mutable", snippet);
 844                                     let suggestion = format!("mut {}", snippet);
 845
 846                                     if let &Categorization::Deref(ref cmt, _) = cat {
 847                                         if let Categorization::Upvar(mc::Upvar {
 848                                             kind: ty::ClosureKind::Fn, ..
 849                                         }) = cmt.cat {
 850                                             db.note(fn_closure_msg);
 851                                         } else {
 852                                             db.span_suggestion(
 853                                                 sp,
 854                                                 msg,
 855                                                 suggestion,
 856                                                 Applicability::Unspecified,
 857                                             );
 858                                         }
 859                                     } else {
 860                                         db.span_suggestion(
 861                                             sp,
 862                                             msg,
 863                                             suggestion,
 864                                             Applicability::Unspecified,
 865                                         );
 866                                     }
 867                                 }
 868                                 _ => {
 869                                     db.span_help(sp, "consider making this binding mutable");
 870                                 }
 871                             }
 872                         }
 873
 874                         db
 875                     }
 876                     BorrowViolation(euv::ClosureCapture(_)) => {
 877                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 878                     }
 879                     BorrowViolation(euv::OverloadedOperator) |
 880                     BorrowViolation(euv::AddrOf) |
 881                     BorrowViolation(euv::RefBinding) |
 882                     BorrowViolation(euv::AutoRef) |
 883                     BorrowViolation(euv::AutoUnsafe) |
 884                     BorrowViolation(euv::ForLoop) |
 885                     BorrowViolation(euv::MatchDiscriminant) => {
 886                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 887                     }
 888                     BorrowViolation(euv::ClosureInvocation) => {
 889                         span_bug!(err.span,
 890                             "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
1089             BorrowViolation(euv::ClosureInvocation) => {
1090                 is_closure = true;
1091                 "closure invocation"
1092             }
1093
1094             BorrowViolation(euv::ForLoop) => {
1095                 "`for` loop"
1096             }
1097         };
1098
1099         match cause {
1100             mc::AliasableStaticMut => {
1101                 // This path cannot occur. `static mut X` is not checked
1102                 // for aliasability violations.
1103                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1104             }
1105             mc::AliasableStatic | mc::AliasableBorrowed => {}
1106         };
1107         let blame = cmt.immutability_blame();
1108         let mut err = match blame {
1109             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1110                 // FIXME: the distinction between these 2 messages looks wrong.
1111                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1112                     // The aliasability violation with closure captures can
1113                     // happen for nested closures, so we know the enclosing
1114                     // closure incorrectly accepts an `Fn` while it needs to
1115                     // be `FnMut`.
1116                     "consider changing this to accept closures that implement `FnMut`"
1117
1118                 } else {
1119                     "consider changing this closure to take self by mutable reference"
1120                 };
1121                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(id);
1122                 let help_span = self.tcx.hir().span_by_hir_id(hir_id);
1123                 self.cannot_act_on_capture_in_sharable_fn(span,
1124                                                           prefix,
1125                                                           (help_span, help_msg),
1126                                                           Origin::Ast)
1127             }
1128             _ =>  {
1129                 self.cannot_assign_into_immutable_reference(span, prefix,
1130                                                             Origin::Ast)
1131             }
1132         };
1133         self.note_immutability_blame(
1134             &mut err,
1135             blame,
1136             cmt.hir_id
1137         );
1138
1139         if is_closure {
1140             err.help("closures behind references must be called via `&mut`");
1141         }
1142         err.emit();
1143         self.signal_error();
1144     }
1145
1146     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1147     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1148         // Check whether the argument is an immutable reference
1149         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1150         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1151             mutbl: hir::Mutability::MutImmutable,
1152             ref ty
1153         }) = pty.node {
1154             // Account for existing lifetimes when generating the message
1155             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1156                 Ok(snippet) => snippet,
1157                 _ => return None
1158             };
1159
1160             let lifetime_snippet = if !lifetime.is_elided() {
1161                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1162                     Ok(lifetime_snippet) => lifetime_snippet,
1163                     _ => return None
1164                 })
1165             } else {
1166                 String::new()
1167             };
1168             Some(format!("use `&{}mut {}` here to make mutable",
1169                          lifetime_snippet,
1170                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1171         } else {
1172             None
1173         }
1174     }
1175
1176     fn local_binding_mode(&self, hir_id: hir::HirId) -> ty::BindingMode {
1177         let pat = match self.tcx.hir().get_by_hir_id(hir_id) {
1178             Node::Binding(pat) => pat,
1179             node => bug!("bad node for local: {:?}", node)
1180         };
1181
1182         match pat.node {
1183             hir::PatKind::Binding(..) => {
1184                 *self.tables
1185                      .pat_binding_modes()
1186                      .get(pat.hir_id)
1187                      .expect("missing binding mode")
1188             }
1189             _ => bug!("local is not a binding: {:?}", pat)
1190         }
1191     }
1192
1193     fn local_ty(&self, hir_id: hir::HirId) -> (Option<&hir::Ty>, bool) {
1194         let parent = self.tcx.hir().get_parent_node_by_hir_id(hir_id);
1195         let parent_node = self.tcx.hir().get_by_hir_id(parent);
1196
1197         // The parent node is like a fn
1198         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1199             // `nid`'s parent's `Body`
1200             let fn_body = self.tcx.hir().body(fn_like.body());
1201             // Get the position of `node_id` in the arguments list
1202             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.hir_id == hir_id);
1203             if let Some(i) = arg_pos {
1204                 // The argument's `Ty`
1205                 (Some(&fn_like.decl().inputs[i]),
1206                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1207             } else {
1208                 (None, false)
1209             }
1210         } else {
1211             (None, false)
1212         }
1213     }
1214
1215     fn note_immutability_blame(&self,
1216                                db: &mut DiagnosticBuilder<'_>,
1217                                blame: Option<ImmutabilityBlame<'_>>,
1218                                error_hir_id: hir::HirId) {
1219         match blame {
1220             None => {}
1221             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1222             Some(ImmutabilityBlame::ImmLocal(hir_id)) => {
1223                 self.note_immutable_local(db, error_hir_id, hir_id)
1224             }
1225             Some(ImmutabilityBlame::LocalDeref(hir_id)) => {
1226                 match self.local_binding_mode(hir_id) {
1227                     ty::BindByReference(..) => {
1228                         let let_span = self.tcx.hir().span_by_hir_id(hir_id);
1229                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1230                         if let Some(replace_str) = suggestion {
1231                             db.span_suggestion(
1232                                 let_span,
1233                                 "use a mutable reference instead",
1234                                 replace_str,
1235                                 // I believe this can be machine applicable,
1236                                 // but if there are multiple attempted uses of an immutable
1237                                 // reference, I don't know how rustfix handles it, it might
1238                                 // attempt fixing them multiple times.
1239                                 //                              @estebank
1240                                 Applicability::Unspecified,
1241                             );
1242                         }
1243                     }
1244                     ty::BindByValue(..) => {
1245                         if let (Some(local_ty), is_implicit_self) = self.local_ty(hir_id) {
1246                             if let Some(msg) =
1247                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1248                                 db.span_label(local_ty.span, msg);
1249                             }
1250                         }
1251                     }
1252                 }
1253             }
1254             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1255                 let hir_id = match self.tcx.hir().as_local_hir_id(field.did) {
1256                     Some(hir_id) => hir_id,
1257                     None => return
1258                 };
1259
1260                 if let Node::Field(ref field) = self.tcx.hir().get_by_hir_id(hir_id) {
1261                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1262                         db.span_label(field.ty.span, msg);
1263                     }
1264                 }
1265             }
1266         }
1267     }
1268
1269      // Suggest a fix when trying to mutably borrow an immutable local
1270      // binding: either to make the binding mutable (if its type is
1271      // not a mutable reference) or to avoid borrowing altogether
1272     fn note_immutable_local(&self,
1273                             db: &mut DiagnosticBuilder<'_>,
1274                             borrowed_hir_id: hir::HirId,
1275                             binding_hir_id: hir::HirId) {
1276         let let_span = self.tcx.hir().span_by_hir_id(binding_hir_id);
1277         if let ty::BindByValue(..) = self.local_binding_mode(binding_hir_id) {
1278             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1279                 let (ty, is_implicit_self) = self.local_ty(binding_hir_id);
1280                 if is_implicit_self && snippet != "self" {
1281                     // avoid suggesting `mut &self`.
1282                     return
1283                 }
1284                 if let Some(&hir::TyKind::Rptr(
1285                     _,
1286                     hir::MutTy {
1287                         mutbl: hir::MutMutable,
1288                         ..
1289                     },
1290                 )) = ty.map(|t| &t.node)
1291                 {
1292                     let borrow_expr_id = self.tcx.hir().get_parent_node_by_hir_id(borrowed_hir_id);
1293                     db.span_suggestion(
1294                         self.tcx.hir().span_by_hir_id(borrow_expr_id),
1295                         "consider removing the `&mut`, as it is an \
1296                         immutable binding to a mutable reference",
1297                         snippet,
1298                         Applicability::MachineApplicable,
1299                     );
1300                 } else {
1301                     db.span_suggestion(
1302                         let_span,
1303                         "make this binding mutable",
1304                         format!("mut {}", snippet),
1305                         Applicability::MachineApplicable,
1306                     );
1307                 }
1308             }
1309         }
1310     }
1311
1312     fn report_out_of_scope_escaping_closure_capture(&self,
1313                                                     err: &BckError<'a, 'tcx>,
1314                                                     capture_span: Span)
1315     {
1316         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1317
1318         let suggestion =
1319             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1320                 Ok(string) => format!("move {}", string),
1321                 Err(_) => "move |<args>| <body>".to_string()
1322             };
1323
1324         self.cannot_capture_in_long_lived_closure(err.span,
1325                                                   &cmt_path_or_string,
1326                                                   capture_span,
1327                                                   Origin::Ast)
1328             .span_suggestion(
1329                  err.span,
1330                  &format!("to force the closure to take ownership of {} \
1331                            (and any other referenced variables), \
1332                            use the `move` keyword",
1333                            cmt_path_or_string),
1334                  suggestion,
1335                  Applicability::MachineApplicable,
1336             )
1337             .emit();
1338         self.signal_error();
1339     }
1340
1341     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1342         match *region {
1343             ty::ReScope(scope) => {
1344                 Some(self.tcx.sess.source_map().end_point(
1345                         scope.span(self.tcx, &self.region_scope_tree)))
1346             }
1347             _ => None
1348         }
1349     }
1350
1351     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder<'_>, err: &BckError<'a, 'tcx>,
1352                                     error_span: &Span) {
1353         match err.cmt.note {
1354             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1355                 // If this is an `Fn` closure, it simply can't mutate upvars.
1356                 // If it's an `FnMut` closure, the original variable was declared immutable.
1357                 // We need to determine which is the case here.
1358                 let kind = match err.cmt.upvar_cat().unwrap() {
1359                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1360                     _ => bug!()
1361                 };
1362                 if *kind == ty::ClosureKind::Fn {
1363                     let closure_hir_id =
1364                         self.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id);
1365                     db.span_help(self.tcx.hir().span_by_hir_id(closure_hir_id),
1366                                  "consider changing this closure to take \
1367                                   self by mutable reference");
1368                 }
1369             }
1370             _ => {
1371                 if let Categorization::Deref(..) = err.cmt.cat {
1372                     db.span_label(*error_span, "cannot borrow as mutable");
1373                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1374                     let span = self.tcx.hir().span_by_hir_id(local_id);
1375                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1376                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1377                             db.span_label(*error_span, "cannot reborrow mutably");
1378                             db.span_label(*error_span, "try removing `&mut` here");
1379                         } else {
1380                             db.span_label(*error_span, "cannot borrow mutably");
1381                         }
1382                     } else {
1383                         db.span_label(*error_span, "cannot borrow mutably");
1384                     }
1385                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1386                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1387                         db.span_label(*error_span,
1388                                       "cannot mutably borrow field of immutable binding");
1389                     }
1390                 }
1391             }
1392         }
1393     }
1394     pub fn append_loan_path_to_string(&self,
1395                                       loan_path: &LoanPath<'tcx>,
1396                                       out: &mut String) {
1397         match loan_path.kind {
1398             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id }, closure_expr_id: _ }) => {
1399                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1400             }
1401             LpVar(id) => {
1402                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1403             }
1404
1405             LpDowncast(ref lp_base, variant_def_id) => {
1406                 out.push('(');
1407                 self.append_loan_path_to_string(&lp_base, out);
1408                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1409                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1410                 out.push(')');
1411             }
1412
1413             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1414                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1415                 out.push('.');
1416                 out.push_str(&info.as_str());
1417             }
1418
1419             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1420                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1421                 out.push_str("[..]");
1422             }
1423
1424             LpExtend(ref lp_base, _, LpDeref(_)) => {
1425                 out.push('*');
1426                 self.append_loan_path_to_string(&lp_base, out);
1427             }
1428         }
1429     }
1430
1431     pub fn append_autoderefd_loan_path_to_string(&self,
1432                                                  loan_path: &LoanPath<'tcx>,
1433                                                  out: &mut String) {
1434         match loan_path.kind {
1435             LpExtend(ref lp_base, _, LpDeref(_)) => {
1436                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1437                 // rules would normally allow users to omit the `*x`.
1438                 // So just serialize such paths to `x.f` or x[3]` respectively.
1439                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1440             }
1441
1442             LpDowncast(ref lp_base, variant_def_id) => {
1443                 out.push('(');
1444                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1445                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1446                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1447                 out.push(')');
1448             }
1449
1450             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1451                 self.append_loan_path_to_string(loan_path, out)
1452             }
1453         }
1454     }
1455
1456     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1457         let mut result = String::new();
1458         self.append_loan_path_to_string(loan_path, &mut result);
1459         result
1460     }
1461
1462     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1463         cmt.descriptive_string(self.tcx)
1464     }
1465
1466     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1467         match opt_loan_path(cmt) {
1468             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1469             None => self.cmt_to_cow_str(cmt).into_owned(),
1470         }
1471     }
1472 }
1473
1474 impl BitwiseOperator for LoanDataFlowOperator {
1475     #[inline]
1476     fn join(&self, succ: usize, pred: usize) -> usize {
1477         succ | pred // loans from both preds are in scope
1478     }
1479 }
1480
1481 impl DataFlowOperator for LoanDataFlowOperator {
1482     #[inline]
1483     fn initial_value(&self) -> bool {
1484         false // no loans in scope by default
1485     }
1486 }
1487
1488 impl<'tcx> fmt::Debug for InteriorKind {
1489     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1490         match *self {
1491             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1492             InteriorElement => write!(f, "[]"),
1493         }
1494     }
1495 }
1496
1497 impl<'tcx> fmt::Debug for Loan<'tcx> {
1498     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1499         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1500                self.index,
1501                self.loan_path,
1502                self.kind,
1503                self.gen_scope,
1504                self.kill_scope,
1505                self.restricted_paths)
1506     }
1507 }
1508
1509 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1510     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1511         match self.kind {
1512             LpVar(id) => {
1513                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_string(id)))
1514             }
1515
1516             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1517                 let s = ty::tls::with(|tcx| {
1518                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1519                     tcx.hir().node_to_string(var_node_id)
1520                 });
1521                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1522             }
1523
1524             LpDowncast(ref lp, variant_def_id) => {
1525                 let variant_str = if variant_def_id.is_local() {
1526                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1527                 } else {
1528                     format!("{:?}", variant_def_id)
1529                 };
1530                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1531             }
1532
1533             LpExtend(ref lp, _, LpDeref(_)) => {
1534                 write!(f, "{:?}.*", lp)
1535             }
1536
1537             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1538                 write!(f, "{:?}.{:?}", lp, interior)
1539             }
1540         }
1541     }
1542 }
1543
1544 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1545     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1546         match self.kind {
1547             LpVar(id) => {
1548                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_user_string(id)))
1549             }
1550
1551             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1552                 let s = ty::tls::with(|tcx| {
1553                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1554                     tcx.hir().node_to_string(var_node_id)
1555                 });
1556                 write!(f, "$({} captured by closure)", s)
1557             }
1558
1559             LpDowncast(ref lp, variant_def_id) => {
1560                 let variant_str = if variant_def_id.is_local() {
1561                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1562                 } else {
1563                     format!("{:?}", variant_def_id)
1564                 };
1565                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1566             }
1567
1568             LpExtend(ref lp, _, LpDeref(_)) => {
1569                 write!(f, "{}.*", lp)
1570             }
1571
1572             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1573                 write!(f, "{}.{:?}", lp, interior)
1574             }
1575         }
1576     }
1577 }