src/librustc_borrowck/borrowck/mod.rs

   1 //! See The Book chapter on the borrow checker for more details.
   2
   3 #![allow(non_camel_case_types)]
   4
   5 pub use LoanPathKind::*;
   6 pub use LoanPathElem::*;
   7 pub use bckerr_code::*;
   8 pub use AliasableViolationKind::*;
   9 pub use MovedValueUseKind::*;
  10
  11 use InteriorKind::*;
  12
  13 use rustc::hir::HirId;
  14 use rustc::hir::Node;
  15 use rustc::hir::map::blocks::FnLikeNode;
  16 use rustc::cfg;
  17 use rustc::middle::borrowck::{BorrowCheckResult, SignalledError};
  18 use rustc::hir::def_id::{DefId, LocalDefId};
  19 use rustc::middle::expr_use_visitor as euv;
  20 use rustc::middle::mem_categorization as mc;
  21 use rustc::middle::mem_categorization::Categorization;
  22 use rustc::middle::mem_categorization::ImmutabilityBlame;
  23 use rustc::middle::region;
  24 use rustc::middle::free_region::RegionRelations;
  25 use rustc::ty::{self, Ty, TyCtxt};
  26 use rustc::ty::query::Providers;
  27 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  28 use rustc_mir::util::suggest_ref_mut;
  29 use rustc::util::nodemap::FxHashSet;
  30
  31 use std::borrow::Cow;
  32 use std::cell::{Cell, RefCell};
  33 use std::fmt;
  34 use std::rc::Rc;
  35 use std::hash::{Hash, Hasher};
  36 use syntax::source_map::CompilerDesugaringKind;
  37 use syntax_pos::{MultiSpan, Span};
  38 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
  39 use log::debug;
  40
  41 use rustc::hir;
  42
  43 use crate::dataflow::{DataFlowContext, BitwiseOperator, DataFlowOperator, KillFrom};
  44
  45 pub mod check_loans;
  46
  47 pub mod gather_loans;
  48
  49 pub mod move_data;
  50
  51 #[derive(Clone, Copy)]
  52 pub struct LoanDataFlowOperator;
  53
  54 pub type LoanDataFlow<'tcx> = DataFlowContext<'tcx, LoanDataFlowOperator>;
  55
  56 pub fn check_crate<'tcx>(tcx: TyCtxt<'tcx>) {
  57     tcx.par_body_owners(|body_owner_def_id| {
  58         tcx.ensure().borrowck(body_owner_def_id);
  59     });
  60 }
  61
  62 pub fn provide(providers: &mut Providers<'_>) {
  63     *providers = Providers {
  64         borrowck,
  65         ..*providers
  66     };
  67 }
  68
  69 /// Collection of conclusions determined via borrow checker analyses.
  70 pub struct AnalysisData<'tcx> {
  71     pub all_loans: Vec<Loan<'tcx>>,
  72     pub loans: DataFlowContext<'tcx, LoanDataFlowOperator>,
  73     pub move_data: move_data::FlowedMoveData<'tcx>,
  74 }
  75
  76 fn borrowck<'tcx>(tcx: TyCtxt<'tcx>, owner_def_id: DefId) -> &'tcx BorrowCheckResult {
  77     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  78
  79     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  80
  81     let owner_id = tcx.hir().as_local_hir_id(owner_def_id).unwrap();
  82
  83     match tcx.hir().get(owner_id) {
  84         Node::Ctor(..) => {
  85             // We get invoked with anything that has MIR, but some of
  86             // those things (notably the synthesized constructors from
  87             // tuple structs/variants) do not have an associated body
  88             // and do not need borrowchecking.
  89             return tcx.arena.alloc(BorrowCheckResult {
  90                 used_mut_nodes: Default::default(),
  91                 signalled_any_error: SignalledError::NoErrorsSeen,
  92             })
  93         }
  94         _ => { }
  95     }
  96
  97     let body_id = tcx.hir().body_owned_by(owner_id);
  98     let tables = tcx.typeck_tables_of(owner_def_id);
  99     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 100     let body = tcx.hir().body(body_id);
 101     let mut bccx = BorrowckCtxt {
 102         tcx,
 103         tables,
 104         region_scope_tree,
 105         owner_def_id,
 106         body,
 107         used_mut_nodes: Default::default(),
 108         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 109     };
 110
 111     // Eventually, borrowck will always read the MIR, but at the
 112     // moment we do not. So, for now, we always force MIR to be
 113     // constructed for a given fn, since this may result in errors
 114     // being reported and we want that to happen.
 115     //
 116     // Note that `mir_validated` is a "stealable" result; the
 117     // thief, `optimized_mir()`, forces borrowck, so we know that
 118     // is not yet stolen.
 119     tcx.ensure().mir_validated(owner_def_id);
 120
 121     // option dance because you can't capture an uninitialized variable
 122     // by mut-ref.
 123     let mut cfg = None;
 124     if let Some(AnalysisData { all_loans,
 125                                loans: loan_dfcx,
 126                                move_data: flowed_moves }) =
 127         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 128                                      |bccx| {
 129                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 130                                          cfg.as_mut().unwrap()
 131                                      })
 132     {
 133         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 134     }
 135
 136     tcx.arena.alloc(BorrowCheckResult {
 137         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 138         signalled_any_error: bccx.signalled_any_error.into_inner(),
 139     })
 140 }
 141
 142 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(
 143     this: &mut BorrowckCtxt<'a, 'tcx>,
 144     force_analysis: bool,
 145     body_id: hir::BodyId,
 146     get_cfg: F,
 147 ) -> Option<AnalysisData<'tcx>>
 148 where
 149     F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG,
 150 {
 151     // Check the body of fn items.
 152     let (all_loans, move_data) =
 153         gather_loans::gather_loans_in_fn(this, body_id);
 154
 155     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 156         // large arrays of data inserted as constants can take a lot of
 157         // time and memory to borrow-check - see issue #36799. However,
 158         // they don't have places, so no borrow-check is actually needed.
 159         // Recognize that case and skip borrow-checking.
 160         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 161         return None;
 162     } else {
 163         debug!("propagating loans in {:?}", body_id);
 164     }
 165
 166     let cfg = get_cfg(this);
 167     let mut loan_dfcx =
 168         DataFlowContext::new(this.tcx,
 169                              "borrowck",
 170                              Some(this.body),
 171                              cfg,
 172                              LoanDataFlowOperator,
 173                              all_loans.len());
 174     for (loan_idx, loan) in all_loans.iter().enumerate() {
 175         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 176         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 177                            loan.kill_scope.item_local_id(),
 178                            loan_idx);
 179     }
 180     loan_dfcx.add_kills_from_flow_exits(cfg);
 181     loan_dfcx.propagate(cfg, this.body);
 182
 183     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 184                                                       this,
 185                                                       cfg,
 186                                                       this.body);
 187
 188     Some(AnalysisData { all_loans,
 189                         loans: loan_dfcx,
 190                         move_data:flowed_moves })
 191 }
 192
 193 /// Accessor for introspective clients inspecting `AnalysisData` and
 194 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 195 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 196     tcx: TyCtxt<'tcx>,
 197     body_id: hir::BodyId,
 198     cfg: &cfg::CFG,
 199 ) -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'tcx>) {
 200     let owner_id = tcx.hir().body_owner(body_id);
 201     let owner_def_id = tcx.hir().local_def_id_from_hir_id(owner_id);
 202     let tables = tcx.typeck_tables_of(owner_def_id);
 203     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 204     let body = tcx.hir().body(body_id);
 205     let mut bccx = BorrowckCtxt {
 206         tcx,
 207         tables,
 208         region_scope_tree,
 209         owner_def_id,
 210         body,
 211         used_mut_nodes: Default::default(),
 212         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 213     };
 214
 215     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 216     (bccx, dataflow_data.unwrap())
 217 }
 218
 219 // ----------------------------------------------------------------------
 220 // Type definitions
 221
 222 pub struct BorrowckCtxt<'a, 'tcx> {
 223     tcx: TyCtxt<'tcx>,
 224
 225     // tables for the current thing we are checking; set to
 226     // Some in `borrowck_fn` and cleared later
 227     tables: &'a ty::TypeckTables<'tcx>,
 228
 229     region_scope_tree: &'tcx region::ScopeTree,
 230
 231     owner_def_id: DefId,
 232
 233     body: &'tcx hir::Body,
 234
 235     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 236
 237     signalled_any_error: Cell<SignalledError>,
 238 }
 239
 240 impl BorrowckCtxt<'_, 'tcx> {
 241     fn signal_error(&self) {
 242         self.signalled_any_error.set(SignalledError::SawSomeError);
 243     }
 244 }
 245
 246 impl BorrowckErrors<'a> for &'a BorrowckCtxt<'_, 'tcx> {
 247     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 248                                                      sp: S,
 249                                                      msg: &str,
 250                                                      code: DiagnosticId)
 251                                                      -> DiagnosticBuilder<'a>
 252     {
 253         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 254     }
 255
 256     fn struct_span_err<S: Into<MultiSpan>>(self,
 257                                            sp: S,
 258                                            msg: &str)
 259                                            -> DiagnosticBuilder<'a>
 260     {
 261         self.tcx.sess.struct_span_err(sp, msg)
 262     }
 263
 264     fn cancel_if_wrong_origin(self,
 265                               mut diag: DiagnosticBuilder<'a>,
 266                               o: Origin)
 267                               -> DiagnosticBuilder<'a>
 268     {
 269         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 270             self.tcx.sess.diagnostic().cancel(&mut diag);
 271         }
 272         diag
 273     }
 274 }
 275
 276 ///////////////////////////////////////////////////////////////////////////
 277 // Loans and loan paths
 278
 279 /// Record of a loan that was issued.
 280 pub struct Loan<'tcx> {
 281     index: usize,
 282     loan_path: Rc<LoanPath<'tcx>>,
 283     kind: ty::BorrowKind,
 284     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 285
 286     /// gen_scope indicates where loan is introduced. Typically the
 287     /// loan is introduced at the point of the borrow, but in some
 288     /// cases, notably method arguments, the loan may be introduced
 289     /// only later, once it comes into scope. See also
 290     /// `GatherLoanCtxt::compute_gen_scope`.
 291     gen_scope: region::Scope,
 292
 293     /// kill_scope indicates when the loan goes out of scope. This is
 294     /// either when the lifetime expires or when the local variable
 295     /// which roots the loan-path goes out of scope, whichever happens
 296     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 297     kill_scope: region::Scope,
 298     span: Span,
 299     cause: euv::LoanCause,
 300 }
 301
 302 impl<'tcx> Loan<'tcx> {
 303     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 304         self.loan_path.clone()
 305     }
 306 }
 307
 308 #[derive(Eq)]
 309 pub struct LoanPath<'tcx> {
 310     kind: LoanPathKind<'tcx>,
 311     ty: Ty<'tcx>,
 312 }
 313
 314 impl<'tcx> PartialEq for LoanPath<'tcx> {
 315     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 316         self.kind == that.kind
 317     }
 318 }
 319
 320 impl<'tcx> Hash for LoanPath<'tcx> {
 321     fn hash<H: Hasher>(&self, state: &mut H) {
 322         self.kind.hash(state);
 323     }
 324 }
 325
 326 #[derive(PartialEq, Eq, Hash, Debug)]
 327 pub enum LoanPathKind<'tcx> {
 328     LpVar(hir::HirId),                          // `x` in README.md
 329     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 330     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 331     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 332 }
 333
 334 impl<'tcx> LoanPath<'tcx> {
 335     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 336         LoanPath { kind: kind, ty: ty }
 337     }
 338
 339     fn to_type(&self) -> Ty<'tcx> { self.ty }
 340
 341     fn has_downcast(&self) -> bool {
 342         match self.kind {
 343             LpDowncast(_, _) => true,
 344             LpExtend(ref lp, _, LpInterior(_, _)) => {
 345                 lp.has_downcast()
 346             }
 347             _ => false,
 348         }
 349     }
 350 }
 351
 352 // FIXME (pnkfelix): See discussion here
 353 // https://github.com/pnkfelix/rust/commit/
 354 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 355 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 356
 357 // A local, "cleaned" version of `mc::InteriorKind` that drops
 358 // information that is not relevant to loan-path analysis. (In
 359 // particular, the distinction between how precisely an array-element
 360 // is tracked is irrelevant here.)
 361 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 362 pub enum InteriorKind {
 363     InteriorField(mc::FieldIndex),
 364     InteriorElement,
 365 }
 366
 367 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 368 impl ToInteriorKind for mc::InteriorKind {
 369     fn cleaned(self) -> InteriorKind {
 370         match self {
 371             mc::InteriorField(name) => InteriorField(name),
 372             mc::InteriorElement(_) => InteriorElement,
 373         }
 374     }
 375 }
 376
 377 // This can be:
 378 // - a pointer dereference (`*P` in README.md)
 379 // - a field reference, with an optional definition of the containing
 380 //   enum variant (`P.f` in README.md)
 381 // `DefId` is present when the field is part of struct that is in
 382 // a variant of an enum. For instance in:
 383 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 384 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 385 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 386 pub enum LoanPathElem<'tcx> {
 387     LpDeref(mc::PointerKind<'tcx>),
 388     LpInterior(Option<DefId>, InteriorKind),
 389 }
 390
 391 fn closure_to_block(closure_id: LocalDefId, tcx: TyCtxt<'_>) -> HirId {
 392     let closure_id = tcx.hir().local_def_id_to_hir_id(closure_id);
 393     match tcx.hir().get(closure_id) {
 394         Node::Expr(expr) => match expr.node {
 395             hir::ExprKind::Closure(.., body_id, _, _) => {
 396                 body_id.hir_id
 397             }
 398             _ => {
 399                 bug!("encountered non-closure id: {}", closure_id)
 400             }
 401         },
 402         _ => bug!("encountered non-expr id: {}", closure_id)
 403     }
 404 }
 405
 406 impl LoanPath<'tcx> {
 407     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'_, 'tcx>) -> region::Scope {
 408         match self.kind {
 409             LpVar(hir_id) => {
 410                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 411             }
 412             LpUpvar(upvar_id) => {
 413                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 414                 region::Scope { id: block_id.local_id, data: region::ScopeData::Node }
 415             }
 416             LpDowncast(ref base, _) |
 417             LpExtend(ref base, ..) => base.kill_scope(bccx),
 418         }
 419     }
 420
 421     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 422         match (&self.kind, &other.kind) {
 423             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 424              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 425                 if id == id2 && opt_variant_id == opt_variant_id2 {
 426                     base.has_fork(&base2)
 427                 } else {
 428                     true
 429                 },
 430             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 431             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 432             _ => false,
 433         }
 434     }
 435
 436     fn depth(&self) -> usize {
 437         match self.kind {
 438             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 439             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 440             _ => 0,
 441         }
 442     }
 443
 444     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 445         match (&self.kind, &other.kind) {
 446             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 447              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 448                 if id == id2 && opt_variant_id == opt_variant_id2 {
 449                     base.common(&base2).map(|x| {
 450                         let xd = x.depth();
 451                         if base.depth() == xd && base2.depth() == xd {
 452                             LoanPath {
 453                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 454                                 ty: self.ty,
 455                             }
 456                         } else {
 457                             x
 458                         }
 459                     })
 460                 } else {
 461                     base.common(&base2)
 462                 }
 463             }
 464             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 465             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 466             (&LpVar(id), &LpVar(id2)) => {
 467                 if id == id2 {
 468                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 469                 } else {
 470                     None
 471                 }
 472             }
 473             (&LpUpvar(id), &LpUpvar(id2)) => {
 474                 if id == id2 {
 475                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 476                 } else {
 477                     None
 478                 }
 479             }
 480             _ => None,
 481         }
 482     }
 483 }
 484
 485 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 486 // mutable independently of the struct it belongs to. (#35937)
 487 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 488     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 489
 490     match cmt.cat {
 491         Categorization::Rvalue(..) |
 492         Categorization::ThreadLocal(..) |
 493         Categorization::StaticItem => {
 494             (None, false)
 495         }
 496
 497         Categorization::Local(id) => {
 498             (Some(new_lp(LpVar(id))), false)
 499         }
 500
 501         Categorization::Upvar(mc::Upvar { id, .. }) => {
 502             (Some(new_lp(LpUpvar(id))), false)
 503         }
 504
 505         Categorization::Deref(ref cmt_base, pk) => {
 506             let lp = opt_loan_path_is_field(cmt_base);
 507             (lp.0.map(|lp| {
 508                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 509             }), lp.1)
 510         }
 511
 512         Categorization::Interior(ref cmt_base, ik) => {
 513             (opt_loan_path(cmt_base).map(|lp| {
 514                 let opt_variant_id = match cmt_base.cat {
 515                     Categorization::Downcast(_, did) =>  Some(did),
 516                     _ => None
 517                 };
 518                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 519             }), true)
 520         }
 521
 522         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 523             let lp = opt_loan_path_is_field(cmt_base);
 524             (lp.0.map(|lp| {
 525                 new_lp(LpDowncast(lp, variant_def_id))
 526             }), lp.1)
 527         }
 528     }
 529 }
 530
 531 /// Computes the `LoanPath` (if any) for a `cmt`.
 532 /// Note that this logic is somewhat duplicated in
 533 /// the method `compute()` found in `gather_loans::restrictions`,
 534 /// which allows it to share common loan path pieces as it
 535 /// traverses the CMT.
 536 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 537     opt_loan_path_is_field(cmt).0
 538 }
 539
 540 ///////////////////////////////////////////////////////////////////////////
 541 // Errors
 542
 543 // Errors that can occur
 544 #[derive(Debug, PartialEq)]
 545 pub enum bckerr_code<'tcx> {
 546     err_mutbl,
 547     /// superscope, subscope, loan cause
 548     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 549     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 550 }
 551
 552 // Combination of an error code and the categorization of the expression
 553 // that caused it
 554 #[derive(Debug, PartialEq)]
 555 pub struct BckError<'c, 'tcx> {
 556     span: Span,
 557     cause: AliasableViolationKind,
 558     cmt: &'c mc::cmt_<'tcx>,
 559     code: bckerr_code<'tcx>
 560 }
 561
 562 #[derive(Copy, Clone, Debug, PartialEq)]
 563 pub enum AliasableViolationKind {
 564     MutabilityViolation,
 565     BorrowViolation(euv::LoanCause)
 566 }
 567
 568 #[derive(Copy, Clone, Debug)]
 569 pub enum MovedValueUseKind {
 570     MovedInUse,
 571     MovedInCapture,
 572 }
 573
 574 ///////////////////////////////////////////////////////////////////////////
 575 // Misc
 576
 577 impl BorrowckCtxt<'_, 'tcx> {
 578     pub fn is_subregion_of(&self,
 579                            r_sub: ty::Region<'tcx>,
 580                            r_sup: ty::Region<'tcx>)
 581                            -> bool
 582     {
 583         let region_rels = RegionRelations::new(self.tcx,
 584                                                self.owner_def_id,
 585                                                &self.region_scope_tree,
 586                                                &self.tables.free_region_map);
 587         region_rels.is_subregion_of(r_sub, r_sup)
 588     }
 589
 590     pub fn report(&self, err: BckError<'a, 'tcx>) {
 591         // Catch and handle some particular cases.
 592         match (&err.code, &err.cause) {
 593             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 594              &BorrowViolation(euv::ClosureCapture(span))) |
 595             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 596              &BorrowViolation(euv::ClosureCapture(span))) |
 597             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 598              &BorrowViolation(euv::ClosureCapture(span))) => {
 599                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 600             }
 601             _ => { }
 602         }
 603
 604         self.report_bckerr(&err);
 605     }
 606
 607     pub fn report_use_of_moved_value(&self,
 608                                      use_span: Span,
 609                                      use_kind: MovedValueUseKind,
 610                                      lp: &LoanPath<'tcx>,
 611                                      the_move: &move_data::Move,
 612                                      moved_lp: &LoanPath<'tcx>) {
 613         let (verb, verb_participle) = match use_kind {
 614             MovedInUse => ("use", "used"),
 615             MovedInCapture => ("capture", "captured"),
 616         };
 617
 618         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 619             move_data::Declared => {
 620                 // If this is an uninitialized variable, just emit a simple warning
 621                 // and return.
 622                 self.cannot_act_on_uninitialized_variable(use_span,
 623                                                           verb,
 624                                                           &self.loan_path_to_string(lp),
 625                                                           Origin::Ast)
 626                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 627                                                   self.loan_path_to_string(lp)))
 628                     .emit();
 629                 self.signal_error();
 630                 return;
 631             }
 632             _ => {
 633                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 634                 // normally generate a rather confusing message:
 635                 //
 636                 //     error: use of moved value: `x.b`
 637                 //     note: `x.a` moved here...
 638                 //
 639                 // What we want to do instead is get the 'common ancestor' of the two moves and
 640                 // use that for most of the message instead, giving is something like this:
 641                 //
 642                 //     error: use of moved value: `x`
 643                 //     note: `x` moved here (through moving `x.a`)...
 644
 645                 let common = moved_lp.common(lp);
 646                 let has_common = common.is_some();
 647                 let has_fork = moved_lp.has_fork(lp);
 648                 let (nl, ol, moved_lp_msg) =
 649                     if has_fork && has_common {
 650                         let nl = self.loan_path_to_string(&common.unwrap());
 651                         let ol = nl.clone();
 652                         let moved_lp_msg = format!(" (through moving `{}`)",
 653                                                    self.loan_path_to_string(moved_lp));
 654                         (nl, ol, moved_lp_msg)
 655                     } else {
 656                         (self.loan_path_to_string(lp),
 657                          self.loan_path_to_string(moved_lp),
 658                          String::new())
 659                     };
 660
 661                 let partial = moved_lp.depth() > lp.depth();
 662                 let msg = if !has_fork && partial { "partially " }
 663                           else if has_fork && !has_common { "collaterally "}
 664                 else { "" };
 665                 let mut err = self.cannot_act_on_moved_value(use_span,
 666                                                              verb,
 667                                                              msg,
 668                                                              Some(nl),
 669                                                              Origin::Ast);
 670                 let need_note = match lp.ty.sty {
 671                     ty::Closure(id, _) => {
 672                         let hir_id = self.tcx.hir().as_local_hir_id(id).unwrap();
 673                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 674                             err.span_note(*span, &format!(
 675                                 "closure cannot be invoked more than once because \
 676                                 it moves the variable `{}` out of its environment",
 677                                 name
 678                             ));
 679                             false
 680                         } else {
 681                             true
 682                         }
 683                     }
 684                     _ => true,
 685                 };
 686                 (ol, moved_lp_msg, err, need_note)
 687             }
 688         };
 689
 690         // Get type of value and span where it was previously
 691         // moved.
 692         let hir_id = hir::HirId {
 693             owner: self.body.value.hir_id.owner,
 694             local_id: the_move.id
 695         };
 696         let (move_span, move_note) = match the_move.kind {
 697             move_data::Declared => {
 698                 unreachable!();
 699             }
 700
 701             move_data::MoveExpr |
 702             move_data::MovePat => (self.tcx.hir().span(hir_id), ""),
 703
 704             move_data::Captured =>
 705                 (match self.tcx.hir().expect_expr(hir_id).node {
 706                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 707                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 708                                   the_move.id, r),
 709                 }, " (into closure)"),
 710         };
 711
 712         // Annotate the use and the move in the span. Watch out for
 713         // the case where the use and the move are the same. This
 714         // means the use is in a loop.
 715         err = if use_span == move_span {
 716             err.span_label(
 717                 use_span,
 718                 format!("value moved{} here in previous iteration of loop",
 719                          move_note));
 720             err
 721         } else {
 722             err.span_label(use_span, format!("value {} here after move", verb_participle));
 723             err.span_label(move_span, format!("value moved{} here", move_note));
 724             err
 725         };
 726
 727         if need_note {
 728             err.note(&format!(
 729                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 730                 if moved_lp.has_downcast() {
 731                     "the value".to_string()
 732                 } else {
 733                     format!("`{}`", self.loan_path_to_string(moved_lp))
 734                 },
 735                 moved_lp.ty));
 736         }
 737         if let (Some(CompilerDesugaringKind::ForLoop), Ok(snippet)) = (
 738             move_span.compiler_desugaring_kind(),
 739             self.tcx.sess.source_map().span_to_snippet(move_span),
 740          ) {
 741             if !snippet.starts_with("&") {
 742                 err.span_suggestion(
 743                     move_span,
 744                     "consider borrowing this to avoid moving it into the for loop",
 745                     format!("&{}", snippet),
 746                     Applicability::MaybeIncorrect,
 747                 );
 748             }
 749         }
 750
 751         // Note: we used to suggest adding a `ref binding` or calling
 752         // `clone` but those suggestions have been removed because
 753         // they are often not what you actually want to do, and were
 754         // not considered particularly helpful.
 755
 756         err.emit();
 757         self.signal_error();
 758     }
 759
 760     pub fn report_partial_reinitialization_of_uninitialized_structure(
 761             &self,
 762             span: Span,
 763             lp: &LoanPath<'tcx>) {
 764         self.cannot_partially_reinit_an_uninit_struct(span,
 765                                                       &self.loan_path_to_string(lp),
 766                                                       Origin::Ast)
 767             .emit();
 768         self.signal_error();
 769     }
 770
 771     pub fn report_reassigned_immutable_variable(&self,
 772                                                 span: Span,
 773                                                 lp: &LoanPath<'tcx>,
 774                                                 assign:
 775                                                 &move_data::Assignment) {
 776         let mut err = self.cannot_reassign_immutable(span,
 777                                                      &self.loan_path_to_string(lp),
 778                                                      false,
 779                                                      Origin::Ast);
 780         err.span_label(span, "cannot assign twice to immutable variable");
 781         if span != assign.span {
 782             err.span_label(assign.span, format!("first assignment to `{}`",
 783                                                 self.loan_path_to_string(lp)));
 784         }
 785         err.emit();
 786         self.signal_error();
 787     }
 788
 789     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 790         let error_span = err.span.clone();
 791
 792         match err.code {
 793             err_mutbl => {
 794                 let descr: Cow<'static, str> = match err.cmt.note {
 795                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 796                         self.cmt_to_cow_str(&err.cmt)
 797                     }
 798                     _ => match opt_loan_path_is_field(&err.cmt) {
 799                         (None, true) => {
 800                             format!("{} of {} binding",
 801                                     self.cmt_to_cow_str(&err.cmt),
 802                                     err.cmt.mutbl.to_user_str()).into()
 803
 804                         }
 805                         (None, false) => {
 806                             format!("{} {}",
 807                                     err.cmt.mutbl.to_user_str(),
 808                                     self.cmt_to_cow_str(&err.cmt)).into()
 809
 810                         }
 811                         (Some(lp), true) => {
 812                             format!("{} `{}` of {} binding",
 813                                     self.cmt_to_cow_str(&err.cmt),
 814                                     self.loan_path_to_string(&lp),
 815                                     err.cmt.mutbl.to_user_str()).into()
 816                         }
 817                         (Some(lp), false) => {
 818                             format!("{} {} `{}`",
 819                                     err.cmt.mutbl.to_user_str(),
 820                                     self.cmt_to_cow_str(&err.cmt),
 821                                     self.loan_path_to_string(&lp)).into()
 822                         }
 823                     }
 824                 };
 825
 826                 let mut db = match err.cause {
 827                     MutabilityViolation => {
 828                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 829                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 830                             let hir_id = upvar_id.var_path.hir_id;
 831                             let sp = self.tcx.hir().span(hir_id);
 832                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 833                                                   environment for modifications";
 834                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 835                                 (_, &Categorization::Upvar(mc::Upvar {
 836                                     kind: ty::ClosureKind::Fn, ..
 837                                 })) => {
 838                                     db.note(fn_closure_msg);
 839                                     // we should point at the cause for this closure being
 840                                     // identified as `Fn` (like in signature of method this
 841                                     // closure was passed into)
 842                                 }
 843                                 (Ok(ref snippet), ref cat) => {
 844                                     let msg = &format!("consider making `{}` mutable", snippet);
 845                                     let suggestion = format!("mut {}", snippet);
 846
 847                                     if let &Categorization::Deref(ref cmt, _) = cat {
 848                                         if let Categorization::Upvar(mc::Upvar {
 849                                             kind: ty::ClosureKind::Fn, ..
 850                                         }) = cmt.cat {
 851                                             db.note(fn_closure_msg);
 852                                         } else {
 853                                             db.span_suggestion(
 854                                                 sp,
 855                                                 msg,
 856                                                 suggestion,
 857                                                 Applicability::Unspecified,
 858                                             );
 859                                         }
 860                                     } else {
 861                                         db.span_suggestion(
 862                                             sp,
 863                                             msg,
 864                                             suggestion,
 865                                             Applicability::Unspecified,
 866                                         );
 867                                     }
 868                                 }
 869                                 _ => {
 870                                     db.span_help(sp, "consider making this binding mutable");
 871                                 }
 872                             }
 873                         }
 874
 875                         db
 876                     }
 877                     BorrowViolation(euv::ClosureCapture(_)) => {
 878                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 879                     }
 880                     BorrowViolation(euv::OverloadedOperator) |
 881                     BorrowViolation(euv::AddrOf) |
 882                     BorrowViolation(euv::RefBinding) |
 883                     BorrowViolation(euv::AutoRef) |
 884                     BorrowViolation(euv::AutoUnsafe) |
 885                     BorrowViolation(euv::ForLoop) |
 886                     BorrowViolation(euv::MatchDiscriminant) => {
 887                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 888                     }
 889                     BorrowViolation(euv::ClosureInvocation) => {
 890                         span_bug!(err.span, "err_mutbl with a closure invocation");
 891                     }
 892                 };
 893
 894                 // We add a special note about `IndexMut`, if the source of this error
 895                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 896                 // to implement two traits for "one operator" is not very intuitive for
 897                 // many programmers.
 898                 if err.cmt.note == mc::NoteIndex {
 899                     let node = self.tcx.hir().get(err.cmt.hir_id);
 900
 901                     // This pattern probably always matches.
 902                     if let Node::Expr(
 903                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 904                     ) = node {
 905                         let ty = self.tables.expr_ty(lhs);
 906
 907                         db.help(&format!(
 908                             "trait `IndexMut` is required to modify indexed content, but \
 909                              it is not implemented for `{}`",
 910                             ty
 911                         ));
 912                     }
 913                 }
 914
 915                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 916                 self.note_immutability_blame(
 917                     &mut db,
 918                     err.cmt.immutability_blame(),
 919                     err.cmt.hir_id
 920                 );
 921                 db.emit();
 922                 self.signal_error();
 923             }
 924             err_out_of_scope(super_scope, sub_scope, cause) => {
 925                 let msg = match opt_loan_path(&err.cmt) {
 926                     None => "borrowed value".to_string(),
 927                     Some(lp) => {
 928                         format!("`{}`", self.loan_path_to_string(&lp))
 929                     }
 930                 };
 931
 932                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 933                 let value_kind = match err.cmt.cat {
 934                     mc::Categorization::Rvalue(..) => "temporary value",
 935                     _ => "borrowed value",
 936                 };
 937
 938                 let is_closure = match cause {
 939                     euv::ClosureCapture(s) => {
 940                         // The primary span starts out as the closure creation point.
 941                         // Change the primary span here to highlight the use of the variable
 942                         // in the closure, because it seems more natural. Highlight
 943                         // closure creation point as a secondary span.
 944                         match db.span.primary_span() {
 945                             Some(primary) => {
 946                                 db.span = MultiSpan::from_span(s);
 947                                 db.span_label(primary, "capture occurs here");
 948                                 db.span_label(s, format!("{} does not live long enough",
 949                                                          value_kind));
 950                                 true
 951                             }
 952                             None => false
 953                         }
 954                     }
 955                     _ => {
 956                         db.span_label(error_span, format!("{} does not live long enough",
 957                                                           value_kind));
 958                         false
 959                     }
 960                 };
 961
 962                 let sub_span = self.region_end_span(sub_scope);
 963                 let super_span = self.region_end_span(super_scope);
 964
 965                 match (sub_span, super_span) {
 966                     (Some(s1), Some(s2)) if s1 == s2 => {
 967                         if !is_closure {
 968                             let msg = match opt_loan_path(&err.cmt) {
 969                                 None => value_kind.to_string(),
 970                                 Some(lp) => {
 971                                     format!("`{}`", self.loan_path_to_string(&lp))
 972                                 }
 973                             };
 974                             db.span_label(s1,
 975                                           format!("{} dropped here while still borrowed", msg));
 976                         } else {
 977                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 978                         }
 979                         db.note("values in a scope are dropped in the opposite order \
 980                                 they are created");
 981                     }
 982                     (Some(s1), Some(s2)) if !is_closure => {
 983                         let msg = match opt_loan_path(&err.cmt) {
 984                             None => value_kind.to_string(),
 985                             Some(lp) => {
 986                                 format!("`{}`", self.loan_path_to_string(&lp))
 987                             }
 988                         };
 989                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 990                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 991                     }
 992                     _ => {
 993                         match sub_span {
 994                             Some(s) => {
 995                                 db.span_label(s, format!("{} needs to live until here",
 996                                                           value_kind));
 997                             }
 998                             None => {
 999                                 self.tcx.note_and_explain_region(
1000                                     &self.region_scope_tree,
1001                                     &mut db,
1002                                     "borrowed value must be valid for ",
1003                                     sub_scope,
1004                                     "...");
1005                             }
1006                         }
1007                         match super_span {
1008                             Some(s) => {
1009                                 db.span_label(s, format!("{} only lives until here", value_kind));
1010                             }
1011                             None => {
1012                                 self.tcx.note_and_explain_region(
1013                                     &self.region_scope_tree,
1014                                     &mut db,
1015                                     "...but borrowed value is only valid for ",
1016                                     super_scope,
1017                                     "");
1018                             }
1019                         }
1020                     }
1021                 }
1022
1023                 if let ty::ReScope(scope) = *super_scope {
1024                     let hir_id = scope.hir_id(&self.region_scope_tree);
1025                     match self.tcx.hir().find(hir_id) {
1026                         Some(Node::Stmt(_)) => {
1027                             if *sub_scope != ty::ReStatic {
1028                                 db.note("consider using a `let` binding to increase its lifetime");
1029                             }
1030
1031                         }
1032                         _ => {}
1033                     }
1034                 }
1035
1036                 db.emit();
1037                 self.signal_error();
1038             }
1039             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1040                 let descr = self.cmt_to_path_or_string(err.cmt);
1041                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1042                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1043                     Some(lp) => {
1044                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1045                     }
1046                     None => self.cmt_to_cow_str(&err.cmt)
1047                 };
1048                 self.tcx.note_and_explain_region(
1049                     &self.region_scope_tree,
1050                     &mut db,
1051                     &format!("{} would have to be valid for ",
1052                             descr),
1053                     loan_scope,
1054                     "...");
1055                 self.tcx.note_and_explain_region(
1056                     &self.region_scope_tree,
1057                     &mut db,
1058                     &format!("...but {} is only valid for ", descr),
1059                     ptr_scope,
1060                     "");
1061
1062                 db.emit();
1063                 self.signal_error();
1064             }
1065         }
1066     }
1067
1068     pub fn report_aliasability_violation(&self,
1069                                          span: Span,
1070                                          kind: AliasableViolationKind,
1071                                          cause: mc::AliasableReason,
1072                                          cmt: &mc::cmt_<'tcx>) {
1073         let mut is_closure = false;
1074         let prefix = match kind {
1075             MutabilityViolation => {
1076                 "cannot assign to data"
1077             }
1078             BorrowViolation(euv::ClosureCapture(_)) |
1079             BorrowViolation(euv::OverloadedOperator) |
1080             BorrowViolation(euv::AddrOf) |
1081             BorrowViolation(euv::AutoRef) |
1082             BorrowViolation(euv::AutoUnsafe) |
1083             BorrowViolation(euv::RefBinding) |
1084             BorrowViolation(euv::MatchDiscriminant) => {
1085                 "cannot borrow data mutably"
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(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(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(hir_id);
1193         let parent_node = self.tcx.hir().get(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(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(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(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(borrowed_hir_id);
1291                     db.span_suggestion(
1292                         self.tcx.hir().span(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(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(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(id).as_str());
1398             }
1399             LpVar(id) => {
1400                 out.push_str(&self.tcx.hir().name(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 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, "$({})", ty::tls::with(|tcx| tcx.hir().node_to_string(id)))
1512             }
1513
1514             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1515                 let s = ty::tls::with(|tcx| {
1516                     tcx.hir().node_to_string(var_id)
1517                 });
1518                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1519             }
1520
1521             LpDowncast(ref lp, variant_def_id) => {
1522                 let variant_str = if variant_def_id.is_local() {
1523                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1524                 } else {
1525                     format!("{:?}", variant_def_id)
1526                 };
1527                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1528             }
1529
1530             LpExtend(ref lp, _, LpDeref(_)) => {
1531                 write!(f, "{:?}.*", lp)
1532             }
1533
1534             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1535                 write!(f, "{:?}.{:?}", lp, interior)
1536             }
1537         }
1538     }
1539 }
1540
1541 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1542     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1543         match self.kind {
1544             LpVar(id) => {
1545                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_user_string(id)))
1546             }
1547
1548             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1549                 let s = ty::tls::with(|tcx| {
1550                     tcx.hir().node_to_string(hir_id)
1551                 });
1552                 write!(f, "$({} captured by closure)", s)
1553             }
1554
1555             LpDowncast(ref lp, variant_def_id) => {
1556                 let variant_str = if variant_def_id.is_local() {
1557                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1558                 } else {
1559                     format!("{:?}", variant_def_id)
1560                 };
1561                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1562             }
1563
1564             LpExtend(ref lp, _, LpDeref(_)) => {
1565                 write!(f, "{}.*", lp)
1566             }
1567
1568             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1569                 write!(f, "{}.{:?}", lp, interior)
1570             }
1571         }
1572     }
1573 }