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::source_map::CompilerDesugaringKind;
  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::Ctor(..) => {
  90             // We get invoked with anything that has MIR, but some of
  91             // those things (notably the synthesized constructors from
  92             // tuple structs/variants) do not have an associated body
  93             // and do not need borrowchecking.
  94             return Lrc::new(BorrowCheckResult {
  95                 used_mut_nodes: Default::default(),
  96                 signalled_any_error: SignalledError::NoErrorsSeen,
  97             })
  98         }
  99         _ => { }
 100     }
 101
 102     let body_id = tcx.hir().body_owned_by(owner_id);
 103     let tables = tcx.typeck_tables_of(owner_def_id);
 104     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 105     let body = tcx.hir().body(body_id);
 106     let mut bccx = BorrowckCtxt {
 107         tcx,
 108         tables,
 109         region_scope_tree,
 110         owner_def_id,
 111         body,
 112         used_mut_nodes: Default::default(),
 113         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 114     };
 115
 116     // Eventually, borrowck will always read the MIR, but at the
 117     // moment we do not. So, for now, we always force MIR to be
 118     // constructed for a given fn, since this may result in errors
 119     // being reported and we want that to happen.
 120     //
 121     // Note that `mir_validated` is a "stealable" result; the
 122     // thief, `optimized_mir()`, forces borrowck, so we know that
 123     // is not yet stolen.
 124     tcx.ensure().mir_validated(owner_def_id);
 125
 126     // option dance because you can't capture an uninitialized variable
 127     // by mut-ref.
 128     let mut cfg = None;
 129     if let Some(AnalysisData { all_loans,
 130                                loans: loan_dfcx,
 131                                move_data: flowed_moves }) =
 132         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 133                                      |bccx| {
 134                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 135                                          cfg.as_mut().unwrap()
 136                                      })
 137     {
 138         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 139     }
 140
 141     if !tcx.use_mir_borrowck() {
 142         unused::check(&mut bccx, body);
 143     }
 144
 145     Lrc::new(BorrowCheckResult {
 146         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 147         signalled_any_error: bccx.signalled_any_error.into_inner(),
 148     })
 149 }
 150
 151 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 152                                                  force_analysis: bool,
 153                                                  body_id: hir::BodyId,
 154                                                  get_cfg: F)
 155                                                  -> Option<AnalysisData<'a, 'tcx>>
 156     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 157 {
 158     // Check the body of fn items.
 159     let (all_loans, move_data) =
 160         gather_loans::gather_loans_in_fn(this, body_id);
 161
 162     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 163         // large arrays of data inserted as constants can take a lot of
 164         // time and memory to borrow-check - see issue #36799. However,
 165         // they don't have places, so no borrow-check is actually needed.
 166         // Recognize that case and skip borrow-checking.
 167         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 168         return None;
 169     } else {
 170         debug!("propagating loans in {:?}", body_id);
 171     }
 172
 173     let cfg = get_cfg(this);
 174     let mut loan_dfcx =
 175         DataFlowContext::new(this.tcx,
 176                              "borrowck",
 177                              Some(this.body),
 178                              cfg,
 179                              LoanDataFlowOperator,
 180                              all_loans.len());
 181     for (loan_idx, loan) in all_loans.iter().enumerate() {
 182         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 183         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 184                            loan.kill_scope.item_local_id(),
 185                            loan_idx);
 186     }
 187     loan_dfcx.add_kills_from_flow_exits(cfg);
 188     loan_dfcx.propagate(cfg, this.body);
 189
 190     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 191                                                       this,
 192                                                       cfg,
 193                                                       this.body);
 194
 195     Some(AnalysisData { all_loans,
 196                         loans: loan_dfcx,
 197                         move_data:flowed_moves })
 198 }
 199
 200 /// Accessor for introspective clients inspecting `AnalysisData` and
 201 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 202 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 203     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 204     body_id: hir::BodyId,
 205     cfg: &cfg::CFG)
 206     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 207 {
 208     let owner_id = tcx.hir().body_owner(body_id);
 209     let owner_def_id = tcx.hir().local_def_id(owner_id);
 210     let tables = tcx.typeck_tables_of(owner_def_id);
 211     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 212     let body = tcx.hir().body(body_id);
 213     let mut bccx = BorrowckCtxt {
 214         tcx,
 215         tables,
 216         region_scope_tree,
 217         owner_def_id,
 218         body,
 219         used_mut_nodes: Default::default(),
 220         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 221     };
 222
 223     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 224     (bccx, dataflow_data.unwrap())
 225 }
 226
 227 // ----------------------------------------------------------------------
 228 // Type definitions
 229
 230 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 231     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 232
 233     // tables for the current thing we are checking; set to
 234     // Some in `borrowck_fn` and cleared later
 235     tables: &'a ty::TypeckTables<'tcx>,
 236
 237     region_scope_tree: Lrc<region::ScopeTree>,
 238
 239     owner_def_id: DefId,
 240
 241     body: &'tcx hir::Body,
 242
 243     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 244
 245     signalled_any_error: Cell<SignalledError>,
 246 }
 247
 248
 249 impl<'a, 'tcx: 'a> BorrowckCtxt<'a, 'tcx> {
 250     fn signal_error(&self) {
 251         self.signalled_any_error.set(SignalledError::SawSomeError);
 252     }
 253 }
 254
 255 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 256     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 257                                                      sp: S,
 258                                                      msg: &str,
 259                                                      code: DiagnosticId)
 260                                                      -> DiagnosticBuilder<'a>
 261     {
 262         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 263     }
 264
 265     fn struct_span_err<S: Into<MultiSpan>>(self,
 266                                            sp: S,
 267                                            msg: &str)
 268                                            -> DiagnosticBuilder<'a>
 269     {
 270         self.tcx.sess.struct_span_err(sp, msg)
 271     }
 272
 273     fn cancel_if_wrong_origin(self,
 274                               mut diag: DiagnosticBuilder<'a>,
 275                               o: Origin)
 276                               -> DiagnosticBuilder<'a>
 277     {
 278         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 279             self.tcx.sess.diagnostic().cancel(&mut diag);
 280         }
 281         diag
 282     }
 283 }
 284
 285 ///////////////////////////////////////////////////////////////////////////
 286 // Loans and loan paths
 287
 288 /// Record of a loan that was issued.
 289 pub struct Loan<'tcx> {
 290     index: usize,
 291     loan_path: Rc<LoanPath<'tcx>>,
 292     kind: ty::BorrowKind,
 293     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 294
 295     /// gen_scope indicates where loan is introduced. Typically the
 296     /// loan is introduced at the point of the borrow, but in some
 297     /// cases, notably method arguments, the loan may be introduced
 298     /// only later, once it comes into scope. See also
 299     /// `GatherLoanCtxt::compute_gen_scope`.
 300     gen_scope: region::Scope,
 301
 302     /// kill_scope indicates when the loan goes out of scope. This is
 303     /// either when the lifetime expires or when the local variable
 304     /// which roots the loan-path goes out of scope, whichever happens
 305     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 306     kill_scope: region::Scope,
 307     span: Span,
 308     cause: euv::LoanCause,
 309 }
 310
 311 impl<'tcx> Loan<'tcx> {
 312     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 313         self.loan_path.clone()
 314     }
 315 }
 316
 317 #[derive(Eq)]
 318 pub struct LoanPath<'tcx> {
 319     kind: LoanPathKind<'tcx>,
 320     ty: Ty<'tcx>,
 321 }
 322
 323 impl<'tcx> PartialEq for LoanPath<'tcx> {
 324     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 325         self.kind == that.kind
 326     }
 327 }
 328
 329 impl<'tcx> Hash for LoanPath<'tcx> {
 330     fn hash<H: Hasher>(&self, state: &mut H) {
 331         self.kind.hash(state);
 332     }
 333 }
 334
 335 #[derive(PartialEq, Eq, Hash, Debug)]
 336 pub enum LoanPathKind<'tcx> {
 337     LpVar(hir::HirId),                          // `x` in README.md
 338     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 339     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 340     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 341 }
 342
 343 impl<'tcx> LoanPath<'tcx> {
 344     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 345         LoanPath { kind: kind, ty: ty }
 346     }
 347
 348     fn to_type(&self) -> Ty<'tcx> { self.ty }
 349
 350     fn has_downcast(&self) -> bool {
 351         match self.kind {
 352             LpDowncast(_, _) => true,
 353             LpExtend(ref lp, _, LpInterior(_, _)) => {
 354                 lp.has_downcast()
 355             }
 356             _ => false,
 357         }
 358     }
 359 }
 360
 361 // FIXME (pnkfelix): See discussion here
 362 // https://github.com/pnkfelix/rust/commit/
 363 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 364 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 365
 366 // A local, "cleaned" version of `mc::InteriorKind` that drops
 367 // information that is not relevant to loan-path analysis. (In
 368 // particular, the distinction between how precisely an array-element
 369 // is tracked is irrelevant here.)
 370 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 371 pub enum InteriorKind {
 372     InteriorField(mc::FieldIndex),
 373     InteriorElement,
 374 }
 375
 376 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 377 impl ToInteriorKind for mc::InteriorKind {
 378     fn cleaned(self) -> InteriorKind {
 379         match self {
 380             mc::InteriorField(name) => InteriorField(name),
 381             mc::InteriorElement(_) => InteriorElement,
 382         }
 383     }
 384 }
 385
 386 // This can be:
 387 // - a pointer dereference (`*P` in README.md)
 388 // - a field reference, with an optional definition of the containing
 389 //   enum variant (`P.f` in README.md)
 390 // `DefId` is present when the field is part of struct that is in
 391 // a variant of an enum. For instance in:
 392 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 393 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 394 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 395 pub enum LoanPathElem<'tcx> {
 396     LpDeref(mc::PointerKind<'tcx>),
 397     LpInterior(Option<DefId>, InteriorKind),
 398 }
 399
 400 fn closure_to_block(closure_id: LocalDefId,
 401                     tcx: TyCtxt<'_, '_, '_>) -> HirId {
 402     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 403     match tcx.hir().get(closure_id) {
 404         Node::Expr(expr) => match expr.node {
 405             hir::ExprKind::Closure(.., body_id, _, _) => {
 406                 body_id.hir_id
 407             }
 408             _ => {
 409                 bug!("encountered non-closure id: {}", closure_id)
 410             }
 411         },
 412         _ => bug!("encountered non-expr id: {}", closure_id)
 413     }
 414 }
 415
 416 impl<'a, 'tcx> LoanPath<'tcx> {
 417     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 418         match self.kind {
 419             LpVar(hir_id) => {
 420                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 421             }
 422             LpUpvar(upvar_id) => {
 423                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 424                 region::Scope { id: block_id.local_id, data: region::ScopeData::Node }
 425             }
 426             LpDowncast(ref base, _) |
 427             LpExtend(ref base, ..) => base.kill_scope(bccx),
 428         }
 429     }
 430
 431     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 432         match (&self.kind, &other.kind) {
 433             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 434              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 435                 if id == id2 && opt_variant_id == opt_variant_id2 {
 436                     base.has_fork(&base2)
 437                 } else {
 438                     true
 439                 },
 440             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 441             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 442             _ => false,
 443         }
 444     }
 445
 446     fn depth(&self) -> usize {
 447         match self.kind {
 448             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 449             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 450             _ => 0,
 451         }
 452     }
 453
 454     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 455         match (&self.kind, &other.kind) {
 456             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 457              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 458                 if id == id2 && opt_variant_id == opt_variant_id2 {
 459                     base.common(&base2).map(|x| {
 460                         let xd = x.depth();
 461                         if base.depth() == xd && base2.depth() == xd {
 462                             LoanPath {
 463                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 464                                 ty: self.ty,
 465                             }
 466                         } else {
 467                             x
 468                         }
 469                     })
 470                 } else {
 471                     base.common(&base2)
 472                 }
 473             }
 474             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 475             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 476             (&LpVar(id), &LpVar(id2)) => {
 477                 if id == id2 {
 478                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 479                 } else {
 480                     None
 481                 }
 482             }
 483             (&LpUpvar(id), &LpUpvar(id2)) => {
 484                 if id == id2 {
 485                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 486                 } else {
 487                     None
 488                 }
 489             }
 490             _ => None,
 491         }
 492     }
 493 }
 494
 495 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 496 // mutable independently of the struct it belongs to. (#35937)
 497 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 498     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 499
 500     match cmt.cat {
 501         Categorization::Rvalue(..) |
 502         Categorization::ThreadLocal(..) |
 503         Categorization::StaticItem => {
 504             (None, false)
 505         }
 506
 507         Categorization::Local(id) => {
 508             (Some(new_lp(LpVar(id))), false)
 509         }
 510
 511         Categorization::Upvar(mc::Upvar { id, .. }) => {
 512             (Some(new_lp(LpUpvar(id))), false)
 513         }
 514
 515         Categorization::Deref(ref cmt_base, pk) => {
 516             let lp = opt_loan_path_is_field(cmt_base);
 517             (lp.0.map(|lp| {
 518                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 519             }), lp.1)
 520         }
 521
 522         Categorization::Interior(ref cmt_base, ik) => {
 523             (opt_loan_path(cmt_base).map(|lp| {
 524                 let opt_variant_id = match cmt_base.cat {
 525                     Categorization::Downcast(_, did) =>  Some(did),
 526                     _ => None
 527                 };
 528                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 529             }), true)
 530         }
 531
 532         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 533             let lp = opt_loan_path_is_field(cmt_base);
 534             (lp.0.map(|lp| {
 535                 new_lp(LpDowncast(lp, variant_def_id))
 536             }), lp.1)
 537         }
 538     }
 539 }
 540
 541 /// Computes the `LoanPath` (if any) for a `cmt`.
 542 /// Note that this logic is somewhat duplicated in
 543 /// the method `compute()` found in `gather_loans::restrictions`,
 544 /// which allows it to share common loan path pieces as it
 545 /// traverses the CMT.
 546 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 547     opt_loan_path_is_field(cmt).0
 548 }
 549
 550 ///////////////////////////////////////////////////////////////////////////
 551 // Errors
 552
 553 // Errors that can occur
 554 #[derive(Debug, PartialEq)]
 555 pub enum bckerr_code<'tcx> {
 556     err_mutbl,
 557     /// superscope, subscope, loan cause
 558     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 559     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 560 }
 561
 562 // Combination of an error code and the categorization of the expression
 563 // that caused it
 564 #[derive(Debug, PartialEq)]
 565 pub struct BckError<'c, 'tcx: 'c> {
 566     span: Span,
 567     cause: AliasableViolationKind,
 568     cmt: &'c mc::cmt_<'tcx>,
 569     code: bckerr_code<'tcx>
 570 }
 571
 572 #[derive(Copy, Clone, Debug, PartialEq)]
 573 pub enum AliasableViolationKind {
 574     MutabilityViolation,
 575     BorrowViolation(euv::LoanCause)
 576 }
 577
 578 #[derive(Copy, Clone, Debug)]
 579 pub enum MovedValueUseKind {
 580     MovedInUse,
 581     MovedInCapture,
 582 }
 583
 584 ///////////////////////////////////////////////////////////////////////////
 585 // Misc
 586
 587 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 588     pub fn is_subregion_of(&self,
 589                            r_sub: ty::Region<'tcx>,
 590                            r_sup: ty::Region<'tcx>)
 591                            -> bool
 592     {
 593         let region_rels = RegionRelations::new(self.tcx,
 594                                                self.owner_def_id,
 595                                                &self.region_scope_tree,
 596                                                &self.tables.free_region_map);
 597         region_rels.is_subregion_of(r_sub, r_sup)
 598     }
 599
 600     pub fn report(&self, err: BckError<'a, 'tcx>) {
 601         // Catch and handle some particular cases.
 602         match (&err.code, &err.cause) {
 603             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 604              &BorrowViolation(euv::ClosureCapture(span))) |
 605             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 606              &BorrowViolation(euv::ClosureCapture(span))) |
 607             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 608              &BorrowViolation(euv::ClosureCapture(span))) => {
 609                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 610             }
 611             _ => { }
 612         }
 613
 614         self.report_bckerr(&err);
 615     }
 616
 617     pub fn report_use_of_moved_value(&self,
 618                                      use_span: Span,
 619                                      use_kind: MovedValueUseKind,
 620                                      lp: &LoanPath<'tcx>,
 621                                      the_move: &move_data::Move,
 622                                      moved_lp: &LoanPath<'tcx>) {
 623         let (verb, verb_participle) = match use_kind {
 624             MovedInUse => ("use", "used"),
 625             MovedInCapture => ("capture", "captured"),
 626         };
 627
 628         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 629             move_data::Declared => {
 630                 // If this is an uninitialized variable, just emit a simple warning
 631                 // and return.
 632                 self.cannot_act_on_uninitialized_variable(use_span,
 633                                                           verb,
 634                                                           &self.loan_path_to_string(lp),
 635                                                           Origin::Ast)
 636                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 637                                                   self.loan_path_to_string(lp)))
 638                     .emit();
 639                 self.signal_error();
 640                 return;
 641             }
 642             _ => {
 643                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 644                 // normally generate a rather confusing message:
 645                 //
 646                 //     error: use of moved value: `x.b`
 647                 //     note: `x.a` moved here...
 648                 //
 649                 // What we want to do instead is get the 'common ancestor' of the two moves and
 650                 // use that for most of the message instead, giving is something like this:
 651                 //
 652                 //     error: use of moved value: `x`
 653                 //     note: `x` moved here (through moving `x.a`)...
 654
 655                 let common = moved_lp.common(lp);
 656                 let has_common = common.is_some();
 657                 let has_fork = moved_lp.has_fork(lp);
 658                 let (nl, ol, moved_lp_msg) =
 659                     if has_fork && has_common {
 660                         let nl = self.loan_path_to_string(&common.unwrap());
 661                         let ol = nl.clone();
 662                         let moved_lp_msg = format!(" (through moving `{}`)",
 663                                                    self.loan_path_to_string(moved_lp));
 664                         (nl, ol, moved_lp_msg)
 665                     } else {
 666                         (self.loan_path_to_string(lp),
 667                          self.loan_path_to_string(moved_lp),
 668                          String::new())
 669                     };
 670
 671                 let partial = moved_lp.depth() > lp.depth();
 672                 let msg = if !has_fork && partial { "partially " }
 673                           else if has_fork && !has_common { "collaterally "}
 674                 else { "" };
 675                 let mut err = self.cannot_act_on_moved_value(use_span,
 676                                                              verb,
 677                                                              msg,
 678                                                              Some(nl),
 679                                                              Origin::Ast);
 680                 let need_note = match lp.ty.sty {
 681                     ty::Closure(id, _) => {
 682                         let hir_id = self.tcx.hir().as_local_hir_id(id).unwrap();
 683                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 684                             err.span_note(*span, &format!(
 685                                 "closure cannot be invoked more than once because \
 686                                 it moves the variable `{}` out of its environment",
 687                                 name
 688                             ));
 689                             false
 690                         } else {
 691                             true
 692                         }
 693                     }
 694                     _ => true,
 695                 };
 696                 (ol, moved_lp_msg, err, need_note)
 697             }
 698         };
 699
 700         // Get type of value and span where it was previously
 701         // moved.
 702         let hir_id = hir::HirId {
 703             owner: self.body.value.hir_id.owner,
 704             local_id: the_move.id
 705         };
 706         let (move_span, move_note) = match the_move.kind {
 707             move_data::Declared => {
 708                 unreachable!();
 709             }
 710
 711             move_data::MoveExpr |
 712             move_data::MovePat => (self.tcx.hir().span_by_hir_id(hir_id), ""),
 713
 714             move_data::Captured =>
 715                 (match self.tcx.hir().expect_expr_by_hir_id(hir_id).node {
 716                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 717                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 718                                   the_move.id, r),
 719                 }, " (into closure)"),
 720         };
 721
 722         // Annotate the use and the move in the span. Watch out for
 723         // the case where the use and the move are the same. This
 724         // means the use is in a loop.
 725         err = if use_span == move_span {
 726             err.span_label(
 727                 use_span,
 728                 format!("value moved{} here in previous iteration of loop",
 729                          move_note));
 730             err
 731         } else {
 732             err.span_label(use_span, format!("value {} here after move", verb_participle));
 733             err.span_label(move_span, format!("value moved{} here", move_note));
 734             err
 735         };
 736
 737         if need_note {
 738             err.note(&format!(
 739                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 740                 if moved_lp.has_downcast() {
 741                     "the value".to_string()
 742                 } else {
 743                     format!("`{}`", self.loan_path_to_string(moved_lp))
 744                 },
 745                 moved_lp.ty));
 746         }
 747         if let (Some(CompilerDesugaringKind::ForLoop), Ok(snippet)) = (
 748             move_span.compiler_desugaring_kind(),
 749             self.tcx.sess.source_map().span_to_snippet(move_span),
 750          ) {
 751             if !snippet.starts_with("&") {
 752                 err.span_suggestion(
 753                     move_span,
 754                     "consider borrowing this to avoid moving it into the for loop",
 755                     format!("&{}", snippet),
 756                     Applicability::MaybeIncorrect,
 757                 );
 758             }
 759         }
 760
 761         // Note: we used to suggest adding a `ref binding` or calling
 762         // `clone` but those suggestions have been removed because
 763         // they are often not what you actually want to do, and were
 764         // not considered particularly helpful.
 765
 766         err.emit();
 767         self.signal_error();
 768     }
 769
 770     pub fn report_partial_reinitialization_of_uninitialized_structure(
 771             &self,
 772             span: Span,
 773             lp: &LoanPath<'tcx>) {
 774         self.cannot_partially_reinit_an_uninit_struct(span,
 775                                                       &self.loan_path_to_string(lp),
 776                                                       Origin::Ast)
 777             .emit();
 778         self.signal_error();
 779     }
 780
 781     pub fn report_reassigned_immutable_variable(&self,
 782                                                 span: Span,
 783                                                 lp: &LoanPath<'tcx>,
 784                                                 assign:
 785                                                 &move_data::Assignment) {
 786         let mut err = self.cannot_reassign_immutable(span,
 787                                                      &self.loan_path_to_string(lp),
 788                                                      false,
 789                                                      Origin::Ast);
 790         err.span_label(span, "cannot assign twice to immutable variable");
 791         if span != assign.span {
 792             err.span_label(assign.span, format!("first assignment to `{}`",
 793                                                 self.loan_path_to_string(lp)));
 794         }
 795         err.emit();
 796         self.signal_error();
 797     }
 798
 799     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 800         let error_span = err.span.clone();
 801
 802         match err.code {
 803             err_mutbl => {
 804                 let descr: Cow<'static, str> = match err.cmt.note {
 805                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 806                         self.cmt_to_cow_str(&err.cmt)
 807                     }
 808                     _ => match opt_loan_path_is_field(&err.cmt) {
 809                         (None, true) => {
 810                             format!("{} of {} binding",
 811                                     self.cmt_to_cow_str(&err.cmt),
 812                                     err.cmt.mutbl.to_user_str()).into()
 813
 814                         }
 815                         (None, false) => {
 816                             format!("{} {}",
 817                                     err.cmt.mutbl.to_user_str(),
 818                                     self.cmt_to_cow_str(&err.cmt)).into()
 819
 820                         }
 821                         (Some(lp), true) => {
 822                             format!("{} `{}` of {} binding",
 823                                     self.cmt_to_cow_str(&err.cmt),
 824                                     self.loan_path_to_string(&lp),
 825                                     err.cmt.mutbl.to_user_str()).into()
 826                         }
 827                         (Some(lp), false) => {
 828                             format!("{} {} `{}`",
 829                                     err.cmt.mutbl.to_user_str(),
 830                                     self.cmt_to_cow_str(&err.cmt),
 831                                     self.loan_path_to_string(&lp)).into()
 832                         }
 833                     }
 834                 };
 835
 836                 let mut db = match err.cause {
 837                     MutabilityViolation => {
 838                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 839                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 840                             let hir_id = upvar_id.var_path.hir_id;
 841                             let sp = self.tcx.hir().span_by_hir_id(hir_id);
 842                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 843                                                   environment for modifications";
 844                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 845                                 (_, &Categorization::Upvar(mc::Upvar {
 846                                     kind: ty::ClosureKind::Fn, ..
 847                                 })) => {
 848                                     db.note(fn_closure_msg);
 849                                     // we should point at the cause for this closure being
 850                                     // identified as `Fn` (like in signature of method this
 851                                     // closure was passed into)
 852                                 }
 853                                 (Ok(ref snippet), ref cat) => {
 854                                     let msg = &format!("consider making `{}` mutable", snippet);
 855                                     let suggestion = format!("mut {}", snippet);
 856
 857                                     if let &Categorization::Deref(ref cmt, _) = cat {
 858                                         if let Categorization::Upvar(mc::Upvar {
 859                                             kind: ty::ClosureKind::Fn, ..
 860                                         }) = cmt.cat {
 861                                             db.note(fn_closure_msg);
 862                                         } else {
 863                                             db.span_suggestion(
 864                                                 sp,
 865                                                 msg,
 866                                                 suggestion,
 867                                                 Applicability::Unspecified,
 868                                             );
 869                                         }
 870                                     } else {
 871                                         db.span_suggestion(
 872                                             sp,
 873                                             msg,
 874                                             suggestion,
 875                                             Applicability::Unspecified,
 876                                         );
 877                                     }
 878                                 }
 879                                 _ => {
 880                                     db.span_help(sp, "consider making this binding mutable");
 881                                 }
 882                             }
 883                         }
 884
 885                         db
 886                     }
 887                     BorrowViolation(euv::ClosureCapture(_)) => {
 888                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 889                     }
 890                     BorrowViolation(euv::OverloadedOperator) |
 891                     BorrowViolation(euv::AddrOf) |
 892                     BorrowViolation(euv::RefBinding) |
 893                     BorrowViolation(euv::AutoRef) |
 894                     BorrowViolation(euv::AutoUnsafe) |
 895                     BorrowViolation(euv::ForLoop) |
 896                     BorrowViolation(euv::MatchDiscriminant) => {
 897                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 898                     }
 899                     BorrowViolation(euv::ClosureInvocation) => {
 900                         span_bug!(err.span,
 901                             "err_mutbl with a closure invocation");
 902                     }
 903                 };
 904
 905                 // We add a special note about `IndexMut`, if the source of this error
 906                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 907                 // to implement two traits for "one operator" is not very intuitive for
 908                 // many programmers.
 909                 if err.cmt.note == mc::NoteIndex {
 910                     let node_id = self.tcx.hir().hir_to_node_id(err.cmt.hir_id);
 911                     let node =  self.tcx.hir().get(node_id);
 912
 913                     // This pattern probably always matches.
 914                     if let Node::Expr(
 915                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 916                     ) = node {
 917                         let ty = self.tables.expr_ty(lhs);
 918
 919                         db.help(&format!(
 920                             "trait `IndexMut` is required to modify indexed content, but \
 921                              it is not implemented for `{}`",
 922                             ty
 923                         ));
 924                     }
 925                 }
 926
 927                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 928                 self.note_immutability_blame(
 929                     &mut db,
 930                     err.cmt.immutability_blame(),
 931                     err.cmt.hir_id
 932                 );
 933                 db.emit();
 934                 self.signal_error();
 935             }
 936             err_out_of_scope(super_scope, sub_scope, cause) => {
 937                 let msg = match opt_loan_path(&err.cmt) {
 938                     None => "borrowed value".to_string(),
 939                     Some(lp) => {
 940                         format!("`{}`", self.loan_path_to_string(&lp))
 941                     }
 942                 };
 943
 944                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 945                 let value_kind = match err.cmt.cat {
 946                     mc::Categorization::Rvalue(..) => "temporary value",
 947                     _ => "borrowed value",
 948                 };
 949
 950                 let is_closure = match cause {
 951                     euv::ClosureCapture(s) => {
 952                         // The primary span starts out as the closure creation point.
 953                         // Change the primary span here to highlight the use of the variable
 954                         // in the closure, because it seems more natural. Highlight
 955                         // closure creation point as a secondary span.
 956                         match db.span.primary_span() {
 957                             Some(primary) => {
 958                                 db.span = MultiSpan::from_span(s);
 959                                 db.span_label(primary, "capture occurs here");
 960                                 db.span_label(s, format!("{} does not live long enough",
 961                                                          value_kind));
 962                                 true
 963                             }
 964                             None => false
 965                         }
 966                     }
 967                     _ => {
 968                         db.span_label(error_span, format!("{} does not live long enough",
 969                                                           value_kind));
 970                         false
 971                     }
 972                 };
 973
 974                 let sub_span = self.region_end_span(sub_scope);
 975                 let super_span = self.region_end_span(super_scope);
 976
 977                 match (sub_span, super_span) {
 978                     (Some(s1), Some(s2)) if s1 == s2 => {
 979                         if !is_closure {
 980                             let msg = match opt_loan_path(&err.cmt) {
 981                                 None => value_kind.to_string(),
 982                                 Some(lp) => {
 983                                     format!("`{}`", self.loan_path_to_string(&lp))
 984                                 }
 985                             };
 986                             db.span_label(s1,
 987                                           format!("{} dropped here while still borrowed", msg));
 988                         } else {
 989                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 990                         }
 991                         db.note("values in a scope are dropped in the opposite order \
 992                                 they are created");
 993                     }
 994                     (Some(s1), Some(s2)) if !is_closure => {
 995                         let msg = match opt_loan_path(&err.cmt) {
 996                             None => value_kind.to_string(),
 997                             Some(lp) => {
 998                                 format!("`{}`", self.loan_path_to_string(&lp))
 999                             }
1000                         };
1001                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
1002                         db.span_label(s1, format!("{} needs to live until here", value_kind));
1003                     }
1004                     _ => {
1005                         match sub_span {
1006                             Some(s) => {
1007                                 db.span_label(s, format!("{} needs to live until here",
1008                                                           value_kind));
1009                             }
1010                             None => {
1011                                 self.tcx.note_and_explain_region(
1012                                     &self.region_scope_tree,
1013                                     &mut db,
1014                                     "borrowed value must be valid for ",
1015                                     sub_scope,
1016                                     "...");
1017                             }
1018                         }
1019                         match super_span {
1020                             Some(s) => {
1021                                 db.span_label(s, format!("{} only lives until here", value_kind));
1022                             }
1023                             None => {
1024                                 self.tcx.note_and_explain_region(
1025                                     &self.region_scope_tree,
1026                                     &mut db,
1027                                     "...but borrowed value is only valid for ",
1028                                     super_scope,
1029                                     "");
1030                             }
1031                         }
1032                     }
1033                 }
1034
1035                 if let ty::ReScope(scope) = *super_scope {
1036                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1037                     match self.tcx.hir().find(node_id) {
1038                         Some(Node::Stmt(_)) => {
1039                             if *sub_scope != ty::ReStatic {
1040                                 db.note("consider using a `let` binding to increase its lifetime");
1041                             }
1042
1043                         }
1044                         _ => {}
1045                     }
1046                 }
1047
1048                 db.emit();
1049                 self.signal_error();
1050             }
1051             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1052                 let descr = self.cmt_to_path_or_string(err.cmt);
1053                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1054                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1055                     Some(lp) => {
1056                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1057                     }
1058                     None => self.cmt_to_cow_str(&err.cmt)
1059                 };
1060                 self.tcx.note_and_explain_region(
1061                     &self.region_scope_tree,
1062                     &mut db,
1063                     &format!("{} would have to be valid for ",
1064                             descr),
1065                     loan_scope,
1066                     "...");
1067                 self.tcx.note_and_explain_region(
1068                     &self.region_scope_tree,
1069                     &mut db,
1070                     &format!("...but {} is only valid for ", descr),
1071                     ptr_scope,
1072                     "");
1073
1074                 db.emit();
1075                 self.signal_error();
1076             }
1077         }
1078     }
1079
1080     pub fn report_aliasability_violation(&self,
1081                                          span: Span,
1082                                          kind: AliasableViolationKind,
1083                                          cause: mc::AliasableReason,
1084                                          cmt: &mc::cmt_<'tcx>) {
1085         let mut is_closure = false;
1086         let prefix = match kind {
1087             MutabilityViolation => {
1088                 "cannot assign to data"
1089             }
1090             BorrowViolation(euv::ClosureCapture(_)) |
1091             BorrowViolation(euv::OverloadedOperator) |
1092             BorrowViolation(euv::AddrOf) |
1093             BorrowViolation(euv::AutoRef) |
1094             BorrowViolation(euv::AutoUnsafe) |
1095             BorrowViolation(euv::RefBinding) |
1096             BorrowViolation(euv::MatchDiscriminant) => {
1097                 "cannot borrow data mutably"
1098             }
1099
1100             BorrowViolation(euv::ClosureInvocation) => {
1101                 is_closure = true;
1102                 "closure invocation"
1103             }
1104
1105             BorrowViolation(euv::ForLoop) => {
1106                 "`for` loop"
1107             }
1108         };
1109
1110         match cause {
1111             mc::AliasableStaticMut => {
1112                 // This path cannot occur. `static mut X` is not checked
1113                 // for aliasability violations.
1114                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1115             }
1116             mc::AliasableStatic | mc::AliasableBorrowed => {}
1117         };
1118         let blame = cmt.immutability_blame();
1119         let mut err = match blame {
1120             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1121                 // FIXME: the distinction between these 2 messages looks wrong.
1122                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1123                     // The aliasability violation with closure captures can
1124                     // happen for nested closures, so we know the enclosing
1125                     // closure incorrectly accepts an `Fn` while it needs to
1126                     // be `FnMut`.
1127                     "consider changing this to accept closures that implement `FnMut`"
1128
1129                 } else {
1130                     "consider changing this closure to take self by mutable reference"
1131                 };
1132                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(id);
1133                 let help_span = self.tcx.hir().span_by_hir_id(hir_id);
1134                 self.cannot_act_on_capture_in_sharable_fn(span,
1135                                                           prefix,
1136                                                           (help_span, help_msg),
1137                                                           Origin::Ast)
1138             }
1139             _ =>  {
1140                 self.cannot_assign_into_immutable_reference(span, prefix,
1141                                                             Origin::Ast)
1142             }
1143         };
1144         self.note_immutability_blame(
1145             &mut err,
1146             blame,
1147             cmt.hir_id
1148         );
1149
1150         if is_closure {
1151             err.help("closures behind references must be called via `&mut`");
1152         }
1153         err.emit();
1154         self.signal_error();
1155     }
1156
1157     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1158     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1159         // Check whether the argument is an immutable reference
1160         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1161         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1162             mutbl: hir::Mutability::MutImmutable,
1163             ref ty
1164         }) = pty.node {
1165             // Account for existing lifetimes when generating the message
1166             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1167                 Ok(snippet) => snippet,
1168                 _ => return None
1169             };
1170
1171             let lifetime_snippet = if !lifetime.is_elided() {
1172                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1173                     Ok(lifetime_snippet) => lifetime_snippet,
1174                     _ => return None
1175                 })
1176             } else {
1177                 String::new()
1178             };
1179             Some(format!("use `&{}mut {}` here to make mutable",
1180                          lifetime_snippet,
1181                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1182         } else {
1183             None
1184         }
1185     }
1186
1187     fn local_binding_mode(&self, hir_id: hir::HirId) -> ty::BindingMode {
1188         let pat = match self.tcx.hir().get_by_hir_id(hir_id) {
1189             Node::Binding(pat) => pat,
1190             node => bug!("bad node for local: {:?}", node)
1191         };
1192
1193         match pat.node {
1194             hir::PatKind::Binding(..) => {
1195                 *self.tables
1196                      .pat_binding_modes()
1197                      .get(pat.hir_id)
1198                      .expect("missing binding mode")
1199             }
1200             _ => bug!("local is not a binding: {:?}", pat)
1201         }
1202     }
1203
1204     fn local_ty(&self, hir_id: hir::HirId) -> (Option<&hir::Ty>, bool) {
1205         let parent = self.tcx.hir().get_parent_node_by_hir_id(hir_id);
1206         let parent_node = self.tcx.hir().get_by_hir_id(parent);
1207
1208         // The parent node is like a fn
1209         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1210             // `nid`'s parent's `Body`
1211             let fn_body = self.tcx.hir().body(fn_like.body());
1212             // Get the position of `node_id` in the arguments list
1213             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.hir_id == hir_id);
1214             if let Some(i) = arg_pos {
1215                 // The argument's `Ty`
1216                 (Some(&fn_like.decl().inputs[i]),
1217                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1218             } else {
1219                 (None, false)
1220             }
1221         } else {
1222             (None, false)
1223         }
1224     }
1225
1226     fn note_immutability_blame(&self,
1227                                db: &mut DiagnosticBuilder<'_>,
1228                                blame: Option<ImmutabilityBlame<'_>>,
1229                                error_hir_id: hir::HirId) {
1230         match blame {
1231             None => {}
1232             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1233             Some(ImmutabilityBlame::ImmLocal(hir_id)) => {
1234                 self.note_immutable_local(db, error_hir_id, hir_id)
1235             }
1236             Some(ImmutabilityBlame::LocalDeref(hir_id)) => {
1237                 match self.local_binding_mode(hir_id) {
1238                     ty::BindByReference(..) => {
1239                         let let_span = self.tcx.hir().span_by_hir_id(hir_id);
1240                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1241                         if let Some(replace_str) = suggestion {
1242                             db.span_suggestion(
1243                                 let_span,
1244                                 "use a mutable reference instead",
1245                                 replace_str,
1246                                 // I believe this can be machine applicable,
1247                                 // but if there are multiple attempted uses of an immutable
1248                                 // reference, I don't know how rustfix handles it, it might
1249                                 // attempt fixing them multiple times.
1250                                 //                              @estebank
1251                                 Applicability::Unspecified,
1252                             );
1253                         }
1254                     }
1255                     ty::BindByValue(..) => {
1256                         if let (Some(local_ty), is_implicit_self) = self.local_ty(hir_id) {
1257                             if let Some(msg) =
1258                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1259                                 db.span_label(local_ty.span, msg);
1260                             }
1261                         }
1262                     }
1263                 }
1264             }
1265             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1266                 let hir_id = match self.tcx.hir().as_local_hir_id(field.did) {
1267                     Some(hir_id) => hir_id,
1268                     None => return
1269                 };
1270
1271                 if let Node::Field(ref field) = self.tcx.hir().get_by_hir_id(hir_id) {
1272                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1273                         db.span_label(field.ty.span, msg);
1274                     }
1275                 }
1276             }
1277         }
1278     }
1279
1280      // Suggest a fix when trying to mutably borrow an immutable local
1281      // binding: either to make the binding mutable (if its type is
1282      // not a mutable reference) or to avoid borrowing altogether
1283     fn note_immutable_local(&self,
1284                             db: &mut DiagnosticBuilder<'_>,
1285                             borrowed_hir_id: hir::HirId,
1286                             binding_hir_id: hir::HirId) {
1287         let let_span = self.tcx.hir().span_by_hir_id(binding_hir_id);
1288         if let ty::BindByValue(..) = self.local_binding_mode(binding_hir_id) {
1289             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1290                 let (ty, is_implicit_self) = self.local_ty(binding_hir_id);
1291                 if is_implicit_self && snippet != "self" {
1292                     // avoid suggesting `mut &self`.
1293                     return
1294                 }
1295                 if let Some(&hir::TyKind::Rptr(
1296                     _,
1297                     hir::MutTy {
1298                         mutbl: hir::MutMutable,
1299                         ..
1300                     },
1301                 )) = ty.map(|t| &t.node)
1302                 {
1303                     let borrow_expr_id = self.tcx.hir().get_parent_node_by_hir_id(borrowed_hir_id);
1304                     db.span_suggestion(
1305                         self.tcx.hir().span_by_hir_id(borrow_expr_id),
1306                         "consider removing the `&mut`, as it is an \
1307                         immutable binding to a mutable reference",
1308                         snippet,
1309                         Applicability::MachineApplicable,
1310                     );
1311                 } else {
1312                     db.span_suggestion(
1313                         let_span,
1314                         "make this binding mutable",
1315                         format!("mut {}", snippet),
1316                         Applicability::MachineApplicable,
1317                     );
1318                 }
1319             }
1320         }
1321     }
1322
1323     fn report_out_of_scope_escaping_closure_capture(&self,
1324                                                     err: &BckError<'a, 'tcx>,
1325                                                     capture_span: Span)
1326     {
1327         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1328
1329         let suggestion =
1330             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1331                 Ok(string) => format!("move {}", string),
1332                 Err(_) => "move |<args>| <body>".to_string()
1333             };
1334
1335         self.cannot_capture_in_long_lived_closure(err.span,
1336                                                   &cmt_path_or_string,
1337                                                   capture_span,
1338                                                   Origin::Ast)
1339             .span_suggestion(
1340                  err.span,
1341                  &format!("to force the closure to take ownership of {} \
1342                            (and any other referenced variables), \
1343                            use the `move` keyword",
1344                            cmt_path_or_string),
1345                  suggestion,
1346                  Applicability::MachineApplicable,
1347             )
1348             .emit();
1349         self.signal_error();
1350     }
1351
1352     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1353         match *region {
1354             ty::ReScope(scope) => {
1355                 Some(self.tcx.sess.source_map().end_point(
1356                         scope.span(self.tcx, &self.region_scope_tree)))
1357             }
1358             _ => None
1359         }
1360     }
1361
1362     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder<'_>, err: &BckError<'a, 'tcx>,
1363                                     error_span: &Span) {
1364         match err.cmt.note {
1365             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1366                 // If this is an `Fn` closure, it simply can't mutate upvars.
1367                 // If it's an `FnMut` closure, the original variable was declared immutable.
1368                 // We need to determine which is the case here.
1369                 let kind = match err.cmt.upvar_cat().unwrap() {
1370                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1371                     _ => bug!()
1372                 };
1373                 if *kind == ty::ClosureKind::Fn {
1374                     let closure_hir_id =
1375                         self.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id);
1376                     db.span_help(self.tcx.hir().span_by_hir_id(closure_hir_id),
1377                                  "consider changing this closure to take \
1378                                   self by mutable reference");
1379                 }
1380             }
1381             _ => {
1382                 if let Categorization::Deref(..) = err.cmt.cat {
1383                     db.span_label(*error_span, "cannot borrow as mutable");
1384                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1385                     let span = self.tcx.hir().span_by_hir_id(local_id);
1386                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1387                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1388                             db.span_label(*error_span, "cannot reborrow mutably");
1389                             db.span_label(*error_span, "try removing `&mut` here");
1390                         } else {
1391                             db.span_label(*error_span, "cannot borrow mutably");
1392                         }
1393                     } else {
1394                         db.span_label(*error_span, "cannot borrow mutably");
1395                     }
1396                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1397                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1398                         db.span_label(*error_span,
1399                                       "cannot mutably borrow field of immutable binding");
1400                     }
1401                 }
1402             }
1403         }
1404     }
1405     pub fn append_loan_path_to_string(&self,
1406                                       loan_path: &LoanPath<'tcx>,
1407                                       out: &mut String) {
1408         match loan_path.kind {
1409             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id }, closure_expr_id: _ }) => {
1410                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1411             }
1412             LpVar(id) => {
1413                 out.push_str(&self.tcx.hir().name_by_hir_id(id).as_str());
1414             }
1415
1416             LpDowncast(ref lp_base, variant_def_id) => {
1417                 out.push('(');
1418                 self.append_loan_path_to_string(&lp_base, out);
1419                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1420                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1421                 out.push(')');
1422             }
1423
1424             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1425                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1426                 out.push('.');
1427                 out.push_str(&info.as_str());
1428             }
1429
1430             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1431                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1432                 out.push_str("[..]");
1433             }
1434
1435             LpExtend(ref lp_base, _, LpDeref(_)) => {
1436                 out.push('*');
1437                 self.append_loan_path_to_string(&lp_base, out);
1438             }
1439         }
1440     }
1441
1442     pub fn append_autoderefd_loan_path_to_string(&self,
1443                                                  loan_path: &LoanPath<'tcx>,
1444                                                  out: &mut String) {
1445         match loan_path.kind {
1446             LpExtend(ref lp_base, _, LpDeref(_)) => {
1447                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1448                 // rules would normally allow users to omit the `*x`.
1449                 // So just serialize such paths to `x.f` or x[3]` respectively.
1450                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1451             }
1452
1453             LpDowncast(ref lp_base, variant_def_id) => {
1454                 out.push('(');
1455                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1456                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1457                 out.push_str(&self.tcx.def_path_str(variant_def_id));
1458                 out.push(')');
1459             }
1460
1461             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1462                 self.append_loan_path_to_string(loan_path, out)
1463             }
1464         }
1465     }
1466
1467     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1468         let mut result = String::new();
1469         self.append_loan_path_to_string(loan_path, &mut result);
1470         result
1471     }
1472
1473     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1474         cmt.descriptive_string(self.tcx)
1475     }
1476
1477     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1478         match opt_loan_path(cmt) {
1479             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1480             None => self.cmt_to_cow_str(cmt).into_owned(),
1481         }
1482     }
1483 }
1484
1485 impl BitwiseOperator for LoanDataFlowOperator {
1486     #[inline]
1487     fn join(&self, succ: usize, pred: usize) -> usize {
1488         succ | pred // loans from both preds are in scope
1489     }
1490 }
1491
1492 impl DataFlowOperator for LoanDataFlowOperator {
1493     #[inline]
1494     fn initial_value(&self) -> bool {
1495         false // no loans in scope by default
1496     }
1497 }
1498
1499 impl<'tcx> fmt::Debug for InteriorKind {
1500     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1501         match *self {
1502             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1503             InteriorElement => write!(f, "[]"),
1504         }
1505     }
1506 }
1507
1508 impl<'tcx> fmt::Debug for Loan<'tcx> {
1509     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1510         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1511                self.index,
1512                self.loan_path,
1513                self.kind,
1514                self.gen_scope,
1515                self.kill_scope,
1516                self.restricted_paths)
1517     }
1518 }
1519
1520 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1521     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1522         match self.kind {
1523             LpVar(id) => {
1524                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_string(id)))
1525             }
1526
1527             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1528                 let s = ty::tls::with(|tcx| {
1529                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1530                     tcx.hir().node_to_string(var_node_id)
1531                 });
1532                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1533             }
1534
1535             LpDowncast(ref lp, variant_def_id) => {
1536                 let variant_str = if variant_def_id.is_local() {
1537                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1538                 } else {
1539                     format!("{:?}", variant_def_id)
1540                 };
1541                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1542             }
1543
1544             LpExtend(ref lp, _, LpDeref(_)) => {
1545                 write!(f, "{:?}.*", lp)
1546             }
1547
1548             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1549                 write!(f, "{:?}.{:?}", lp, interior)
1550             }
1551         }
1552     }
1553 }
1554
1555 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1556     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1557         match self.kind {
1558             LpVar(id) => {
1559                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().hir_to_user_string(id)))
1560             }
1561
1562             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1563                 let s = ty::tls::with(|tcx| {
1564                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1565                     tcx.hir().node_to_string(var_node_id)
1566                 });
1567                 write!(f, "$({} captured by closure)", s)
1568             }
1569
1570             LpDowncast(ref lp, variant_def_id) => {
1571                 let variant_str = if variant_def_id.is_local() {
1572                     ty::tls::with(|tcx| tcx.def_path_str(variant_def_id))
1573                 } else {
1574                     format!("{:?}", variant_def_id)
1575                 };
1576                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1577             }
1578
1579             LpExtend(ref lp, _, LpDeref(_)) => {
1580                 write!(f, "{}.*", lp)
1581             }
1582
1583             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1584                 write!(f, "{}.{:?}", lp, interior)
1585             }
1586         }
1587     }
1588 }