src/librustc_borrowck/borrowck/mod.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! See The Book chapter on the borrow checker for more details.
  12
  13 #![allow(non_camel_case_types)]
  14
  15 pub use self::LoanPathKind::*;
  16 pub use self::LoanPathElem::*;
  17 pub use self::bckerr_code::*;
  18 pub use self::AliasableViolationKind::*;
  19 pub use self::MovedValueUseKind::*;
  20
  21 use self::InteriorKind::*;
  22
  23 use rustc::hir::HirId;
  24 use rustc::hir::map as hir_map;
  25 use rustc::hir::map::blocks::FnLikeNode;
  26 use rustc::cfg;
  27 use rustc::middle::dataflow::DataFlowContext;
  28 use rustc::middle::dataflow::BitwiseOperator;
  29 use rustc::middle::dataflow::DataFlowOperator;
  30 use rustc::middle::dataflow::KillFrom;
  31 use rustc::middle::borrowck::BorrowCheckResult;
  32 use rustc::hir::def_id::{DefId, LocalDefId};
  33 use rustc::middle::expr_use_visitor as euv;
  34 use rustc::middle::mem_categorization as mc;
  35 use rustc::middle::mem_categorization::Categorization;
  36 use rustc::middle::mem_categorization::ImmutabilityBlame;
  37 use rustc::middle::region;
  38 use rustc::middle::free_region::RegionRelations;
  39 use rustc::ty::{self, Ty, TyCtxt};
  40 use rustc::ty::maps::Providers;
  41 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  42 use rustc::util::nodemap::FxHashSet;
  43
  44 use std::cell::RefCell;
  45 use std::fmt;
  46 use std::rc::Rc;
  47 use std::hash::{Hash, Hasher};
  48 use syntax::ast;
  49 use syntax_pos::{MultiSpan, Span};
  50 use errors::{DiagnosticBuilder, DiagnosticId};
  51
  52 use rustc::hir;
  53 use rustc::hir::intravisit::{self, Visitor};
  54
  55 pub mod check_loans;
  56
  57 pub mod gather_loans;
  58
  59 pub mod move_data;
  60
  61 mod unused;
  62
  63 #[derive(Clone, Copy)]
  64 pub struct LoanDataFlowOperator;
  65
  66 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  67
  68 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  69     for body_owner_def_id in tcx.body_owners() {
  70         tcx.borrowck(body_owner_def_id);
  71     }
  72 }
  73
  74 pub fn provide(providers: &mut Providers) {
  75     *providers = Providers {
  76         borrowck,
  77         ..*providers
  78     };
  79 }
  80
  81 /// Collection of conclusions determined via borrow checker analyses.
  82 pub struct AnalysisData<'a, 'tcx: 'a> {
  83     pub all_loans: Vec<Loan<'tcx>>,
  84     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  85     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  86 }
  87
  88 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  89     -> Rc<BorrowCheckResult>
  90 {
  91     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  92
  93     let owner_id = tcx.hir.as_local_node_id(owner_def_id).unwrap();
  94
  95     match tcx.hir.get(owner_id) {
  96         hir_map::NodeStructCtor(_) |
  97         hir_map::NodeVariant(_) => {
  98             // We get invoked with anything that has MIR, but some of
  99             // those things (notably the synthesized constructors from
 100             // tuple structs/variants) do not have an associated body
 101             // and do not need borrowchecking.
 102             return Rc::new(BorrowCheckResult {
 103                 used_mut_nodes: FxHashSet(),
 104             })
 105         }
 106         _ => { }
 107     }
 108
 109     let body_id = tcx.hir.body_owned_by(owner_id);
 110     let tables = tcx.typeck_tables_of(owner_def_id);
 111     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 112     let body = tcx.hir.body(body_id);
 113     let mut bccx = BorrowckCtxt {
 114         tcx,
 115         tables,
 116         region_scope_tree,
 117         owner_def_id,
 118         body,
 119         used_mut_nodes: RefCell::new(FxHashSet()),
 120     };
 121
 122     // Eventually, borrowck will always read the MIR, but at the
 123     // moment we do not. So, for now, we always force MIR to be
 124     // constructed for a given fn, since this may result in errors
 125     // being reported and we want that to happen.
 126     //
 127     // Note that `mir_validated` is a "stealable" result; the
 128     // thief, `optimized_mir()`, forces borrowck, so we know that
 129     // is not yet stolen.
 130     tcx.mir_validated(owner_def_id).borrow();
 131
 132     // option dance because you can't capture an uninitialized variable
 133     // by mut-ref.
 134     let mut cfg = None;
 135     if let Some(AnalysisData { all_loans,
 136                                loans: loan_dfcx,
 137                                move_data: flowed_moves }) =
 138         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 139                                      |bccx| {
 140                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 141                                          cfg.as_mut().unwrap()
 142                                      })
 143     {
 144         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 145     }
 146     unused::check(&mut bccx, body);
 147
 148     Rc::new(BorrowCheckResult {
 149         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 150     })
 151 }
 152
 153 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 154                                                  force_analysis: bool,
 155                                                  body_id: hir::BodyId,
 156                                                  get_cfg: F)
 157                                                  -> Option<AnalysisData<'a, 'tcx>>
 158     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 159 {
 160     // Check the body of fn items.
 161     let tcx = this.tcx;
 162     let id_range = {
 163         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 164         visitor.visit_body(this.body);
 165         visitor.result()
 166     };
 167     let (all_loans, move_data) =
 168         gather_loans::gather_loans_in_fn(this, body_id);
 169
 170     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 171         // large arrays of data inserted as constants can take a lot of
 172         // time and memory to borrow-check - see issue #36799. However,
 173         // they don't have places, so no borrow-check is actually needed.
 174         // Recognize that case and skip borrow-checking.
 175         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 176         return None;
 177     } else {
 178         debug!("propagating loans in {:?}", body_id);
 179     }
 180
 181     let cfg = get_cfg(this);
 182     let mut loan_dfcx =
 183         DataFlowContext::new(this.tcx,
 184                              "borrowck",
 185                              Some(this.body),
 186                              cfg,
 187                              LoanDataFlowOperator,
 188                              id_range,
 189                              all_loans.len());
 190     for (loan_idx, loan) in all_loans.iter().enumerate() {
 191         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 192         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 193                            loan.kill_scope.item_local_id(),
 194                            loan_idx);
 195     }
 196     loan_dfcx.add_kills_from_flow_exits(cfg);
 197     loan_dfcx.propagate(cfg, this.body);
 198
 199     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 200                                                       this,
 201                                                       cfg,
 202                                                       id_range,
 203                                                       this.body);
 204
 205     Some(AnalysisData { all_loans,
 206                         loans: loan_dfcx,
 207                         move_data:flowed_moves })
 208 }
 209
 210 /// Accessor for introspective clients inspecting `AnalysisData` and
 211 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 212 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 213     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 214     body_id: hir::BodyId,
 215     cfg: &cfg::CFG)
 216     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 217 {
 218     let owner_id = tcx.hir.body_owner(body_id);
 219     let owner_def_id = tcx.hir.local_def_id(owner_id);
 220     let tables = tcx.typeck_tables_of(owner_def_id);
 221     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 222     let body = tcx.hir.body(body_id);
 223     let mut bccx = BorrowckCtxt {
 224         tcx,
 225         tables,
 226         region_scope_tree,
 227         owner_def_id,
 228         body,
 229         used_mut_nodes: RefCell::new(FxHashSet()),
 230     };
 231
 232     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 233     (bccx, dataflow_data.unwrap())
 234 }
 235
 236 // ----------------------------------------------------------------------
 237 // Type definitions
 238
 239 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 240     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 241
 242     // tables for the current thing we are checking; set to
 243     // Some in `borrowck_fn` and cleared later
 244     tables: &'a ty::TypeckTables<'tcx>,
 245
 246     region_scope_tree: Rc<region::ScopeTree>,
 247
 248     owner_def_id: DefId,
 249
 250     body: &'tcx hir::Body,
 251
 252     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 253 }
 254
 255 impl<'b, 'tcx: 'b> BorrowckErrors for BorrowckCtxt<'b, 'tcx> {
 256     fn struct_span_err_with_code<'a, S: Into<MultiSpan>>(&'a 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<'a, S: Into<MultiSpan>>(&'a 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<'a>(&'a self,
 274                                 mut diag: DiagnosticBuilder<'a>,
 275                                 o: Origin)
 276                                 -> DiagnosticBuilder<'a>
 277     {
 278         if !o.should_emit_errors(self.tcx.sess.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(ast::NodeId),                         // `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::FieldName),
 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) -> ast::NodeId {
 402     let closure_id = tcx.hir.local_def_id_to_node_id(closure_id);
 403     match tcx.hir.get(closure_id) {
 404         hir_map::NodeExpr(expr) => match expr.node {
 405             hir::ExprClosure(.., body_id, _, _) => {
 406                 body_id.node_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(local_id) => {
 420                 let hir_id = bccx.tcx.hir.node_to_hir_id(local_id);
 421                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 422             }
 423             LpUpvar(upvar_id) => {
 424                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 425                 let hir_id = bccx.tcx.hir.node_to_hir_id(block_id);
 426                 region::Scope::Node(hir_id.local_id)
 427             }
 428             LpDowncast(ref base, _) |
 429             LpExtend(ref base, ..) => base.kill_scope(bccx),
 430         }
 431     }
 432
 433     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 434         match (&self.kind, &other.kind) {
 435             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 436              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 437                 if id == id2 && opt_variant_id == opt_variant_id2 {
 438                     base.has_fork(&base2)
 439                 } else {
 440                     true
 441                 },
 442             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 443             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 444             _ => false,
 445         }
 446     }
 447
 448     fn depth(&self) -> usize {
 449         match self.kind {
 450             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 451             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 452             _ => 0,
 453         }
 454     }
 455
 456     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 457         match (&self.kind, &other.kind) {
 458             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 459              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 460                 if id == id2 && opt_variant_id == opt_variant_id2 {
 461                     base.common(&base2).map(|x| {
 462                         let xd = x.depth();
 463                         if base.depth() == xd && base2.depth() == xd {
 464                             LoanPath {
 465                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 466                                 ty: self.ty,
 467                             }
 468                         } else {
 469                             x
 470                         }
 471                     })
 472                 } else {
 473                     base.common(&base2)
 474                 }
 475             }
 476             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 477             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 478             (&LpVar(id), &LpVar(id2)) => {
 479                 if id == id2 {
 480                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 481                 } else {
 482                     None
 483                 }
 484             }
 485             (&LpUpvar(id), &LpUpvar(id2)) => {
 486                 if id == id2 {
 487                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 488                 } else {
 489                     None
 490                 }
 491             }
 492             _ => None,
 493         }
 494     }
 495 }
 496
 497 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 498 // mutable independently of the struct it belongs to. (#35937)
 499 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 500     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 501
 502     match cmt.cat {
 503         Categorization::Rvalue(..) |
 504         Categorization::StaticItem => {
 505             (None, false)
 506         }
 507
 508         Categorization::Local(id) => {
 509             (Some(new_lp(LpVar(id))), false)
 510         }
 511
 512         Categorization::Upvar(mc::Upvar { id, .. }) => {
 513             (Some(new_lp(LpUpvar(id))), false)
 514         }
 515
 516         Categorization::Deref(ref cmt_base, pk) => {
 517             let lp = opt_loan_path_is_field(cmt_base);
 518             (lp.0.map(|lp| {
 519                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 520             }), lp.1)
 521         }
 522
 523         Categorization::Interior(ref cmt_base, ik) => {
 524             (opt_loan_path(cmt_base).map(|lp| {
 525                 let opt_variant_id = match cmt_base.cat {
 526                     Categorization::Downcast(_, did) =>  Some(did),
 527                     _ => None
 528                 };
 529                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 530             }), true)
 531         }
 532
 533         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 534             let lp = opt_loan_path_is_field(cmt_base);
 535             (lp.0.map(|lp| {
 536                 new_lp(LpDowncast(lp, variant_def_id))
 537             }), lp.1)
 538         }
 539     }
 540 }
 541
 542 /// Computes the `LoanPath` (if any) for a `cmt`.
 543 /// Note that this logic is somewhat duplicated in
 544 /// the method `compute()` found in `gather_loans::restrictions`,
 545 /// which allows it to share common loan path pieces as it
 546 /// traverses the CMT.
 547 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 548     opt_loan_path_is_field(cmt).0
 549 }
 550
 551 ///////////////////////////////////////////////////////////////////////////
 552 // Errors
 553
 554 // Errors that can occur
 555 #[derive(Debug, PartialEq)]
 556 pub enum bckerr_code<'tcx> {
 557     err_mutbl,
 558     /// superscope, subscope, loan cause
 559     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 560     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 561 }
 562
 563 // Combination of an error code and the categorization of the expression
 564 // that caused it
 565 #[derive(Debug, PartialEq)]
 566 pub struct BckError<'tcx> {
 567     span: Span,
 568     cause: AliasableViolationKind,
 569     cmt: mc::cmt<'tcx>,
 570     code: bckerr_code<'tcx>
 571 }
 572
 573 #[derive(Copy, Clone, Debug, PartialEq)]
 574 pub enum AliasableViolationKind {
 575     MutabilityViolation,
 576     BorrowViolation(euv::LoanCause)
 577 }
 578
 579 #[derive(Copy, Clone, Debug)]
 580 pub enum MovedValueUseKind {
 581     MovedInUse,
 582     MovedInCapture,
 583 }
 584
 585 ///////////////////////////////////////////////////////////////////////////
 586 // Misc
 587
 588 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 589     pub fn is_subregion_of(&self,
 590                            r_sub: ty::Region<'tcx>,
 591                            r_sup: ty::Region<'tcx>)
 592                            -> bool
 593     {
 594         let region_rels = RegionRelations::new(self.tcx,
 595                                                self.owner_def_id,
 596                                                &self.region_scope_tree,
 597                                                &self.tables.free_region_map);
 598         region_rels.is_subregion_of(r_sub, r_sup)
 599     }
 600
 601     pub fn report(&self, err: BckError<'tcx>) {
 602         // Catch and handle some particular cases.
 603         match (&err.code, &err.cause) {
 604             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 605              &BorrowViolation(euv::ClosureCapture(span))) |
 606             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 607              &BorrowViolation(euv::ClosureCapture(span))) |
 608             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 609              &BorrowViolation(euv::ClosureCapture(span))) => {
 610                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 611             }
 612             _ => { }
 613         }
 614
 615         self.report_bckerr(&err);
 616     }
 617
 618     pub fn report_use_of_moved_value(&self,
 619                                      use_span: Span,
 620                                      use_kind: MovedValueUseKind,
 621                                      lp: &LoanPath<'tcx>,
 622                                      the_move: &move_data::Move,
 623                                      moved_lp: &LoanPath<'tcx>,
 624                                      _param_env: ty::ParamEnv<'tcx>) {
 625         let (verb, verb_participle) = match use_kind {
 626             MovedInUse => ("use", "used"),
 627             MovedInCapture => ("capture", "captured"),
 628         };
 629
 630         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 631             move_data::Declared => {
 632                 // If this is an uninitialized variable, just emit a simple warning
 633                 // and return.
 634                 self.cannot_act_on_uninitialized_variable(use_span,
 635                                                           verb,
 636                                                           &self.loan_path_to_string(lp),
 637                                                           Origin::Ast)
 638                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 639                                                   self.loan_path_to_string(lp)))
 640                     .emit();
 641                 return;
 642             }
 643             _ => {
 644                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 645                 // normally generate a rather confusing message:
 646                 //
 647                 //     error: use of moved value: `x.b`
 648                 //     note: `x.a` moved here...
 649                 //
 650                 // What we want to do instead is get the 'common ancestor' of the two moves and
 651                 // use that for most of the message instead, giving is something like this:
 652                 //
 653                 //     error: use of moved value: `x`
 654                 //     note: `x` moved here (through moving `x.a`)...
 655
 656                 let common = moved_lp.common(lp);
 657                 let has_common = common.is_some();
 658                 let has_fork = moved_lp.has_fork(lp);
 659                 let (nl, ol, moved_lp_msg) =
 660                     if has_fork && has_common {
 661                         let nl = self.loan_path_to_string(&common.unwrap());
 662                         let ol = nl.clone();
 663                         let moved_lp_msg = format!(" (through moving `{}`)",
 664                                                    self.loan_path_to_string(moved_lp));
 665                         (nl, ol, moved_lp_msg)
 666                     } else {
 667                         (self.loan_path_to_string(lp),
 668                          self.loan_path_to_string(moved_lp),
 669                          String::new())
 670                     };
 671
 672                 let partial = moved_lp.depth() > lp.depth();
 673                 let msg = if !has_fork && partial { "partially " }
 674                           else if has_fork && !has_common { "collaterally "}
 675                 else { "" };
 676                 let mut err = self.cannot_act_on_moved_value(use_span,
 677                                                              verb,
 678                                                              msg,
 679                                                              &format!("{}", nl),
 680                                                              Origin::Ast);
 681                 let need_note = match lp.ty.sty {
 682                     ty::TypeVariants::TyClosure(id, _) => {
 683                         let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
 684                         let hir_id = self.tcx.hir.node_to_hir_id(node_id);
 685                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 686                             err.span_note(*span, &format!(
 687                                 "closure cannot be invoked more than once because \
 688                                 it moves the variable `{}` out of its environment",
 689                                 name
 690                             ));
 691                             false
 692                         } else {
 693                             true
 694                         }
 695                     }
 696                     _ => true,
 697                 };
 698                 (ol, moved_lp_msg, err, need_note)
 699             }
 700         };
 701
 702         // Get type of value and span where it was previously
 703         // moved.
 704         let node_id = self.tcx.hir.hir_to_node_id(hir::HirId {
 705             owner: self.body.value.hir_id.owner,
 706             local_id: the_move.id
 707         });
 708         let (move_span, move_note) = match the_move.kind {
 709             move_data::Declared => {
 710                 unreachable!();
 711             }
 712
 713             move_data::MoveExpr |
 714             move_data::MovePat => (self.tcx.hir.span(node_id), ""),
 715
 716             move_data::Captured =>
 717                 (match self.tcx.hir.expect_expr(node_id).node {
 718                     hir::ExprClosure(.., fn_decl_span, _) => fn_decl_span,
 719                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 720                                   the_move.id, r),
 721                 }, " (into closure)"),
 722         };
 723
 724         // Annotate the use and the move in the span. Watch out for
 725         // the case where the use and the move are the same. This
 726         // means the use is in a loop.
 727         err = if use_span == move_span {
 728             err.span_label(
 729                 use_span,
 730                 format!("value moved{} here in previous iteration of loop",
 731                          move_note));
 732             err
 733         } else {
 734             err.span_label(use_span, format!("value {} here after move", verb_participle));
 735             err.span_label(move_span, format!("value moved{} here", move_note));
 736             err
 737         };
 738
 739         if need_note {
 740             err.note(&format!(
 741                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 742                 if moved_lp.has_downcast() {
 743                     "the value".to_string()
 744                 } else {
 745                     format!("`{}`", self.loan_path_to_string(moved_lp))
 746                 },
 747                 moved_lp.ty));
 748         }
 749
 750         // Note: we used to suggest adding a `ref binding` or calling
 751         // `clone` but those suggestions have been removed because
 752         // they are often not what you actually want to do, and were
 753         // not considered particularly helpful.
 754
 755         err.emit();
 756     }
 757
 758     pub fn report_partial_reinitialization_of_uninitialized_structure(
 759             &self,
 760             span: Span,
 761             lp: &LoanPath<'tcx>) {
 762         self.cannot_partially_reinit_an_uninit_struct(span,
 763                                                       &self.loan_path_to_string(lp),
 764                                                       Origin::Ast)
 765             .emit();
 766     }
 767
 768     pub fn report_reassigned_immutable_variable(&self,
 769                                                 span: Span,
 770                                                 lp: &LoanPath<'tcx>,
 771                                                 assign:
 772                                                 &move_data::Assignment) {
 773         let mut err = self.cannot_reassign_immutable(span,
 774                                                      &self.loan_path_to_string(lp),
 775                                                      false,
 776                                                      Origin::Ast);
 777         err.span_label(span, "cannot assign twice to immutable variable");
 778         if span != assign.span {
 779             err.span_label(assign.span, format!("first assignment to `{}`",
 780                                                 self.loan_path_to_string(lp)));
 781         }
 782         err.emit();
 783     }
 784
 785     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 786                                                          s: S,
 787                                                          msg: &str,
 788                                                          code: DiagnosticId)
 789                                                          -> DiagnosticBuilder<'a> {
 790         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 791     }
 792
 793     pub fn span_err_with_code<S: Into<MultiSpan>>(
 794         &self,
 795         s: S,
 796         msg: &str,
 797         code: DiagnosticId,
 798     ) {
 799         self.tcx.sess.span_err_with_code(s, msg, code);
 800     }
 801
 802     fn report_bckerr(&self, err: &BckError<'tcx>) {
 803         let error_span = err.span.clone();
 804
 805         match err.code {
 806             err_mutbl => {
 807                 let descr = match err.cmt.note {
 808                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 809                         self.cmt_to_string(&err.cmt)
 810                     }
 811                     _ => match opt_loan_path_is_field(&err.cmt) {
 812                         (None, true) => {
 813                             format!("{} of {} binding",
 814                                     self.cmt_to_string(&err.cmt),
 815                                     err.cmt.mutbl.to_user_str())
 816
 817                         }
 818                         (None, false) => {
 819                             format!("{} {}",
 820                                     err.cmt.mutbl.to_user_str(),
 821                                     self.cmt_to_string(&err.cmt))
 822
 823                         }
 824                         (Some(lp), true) => {
 825                             format!("{} `{}` of {} binding",
 826                                     self.cmt_to_string(&err.cmt),
 827                                     self.loan_path_to_string(&lp),
 828                                     err.cmt.mutbl.to_user_str())
 829                         }
 830                         (Some(lp), false) => {
 831                             format!("{} {} `{}`",
 832                                     err.cmt.mutbl.to_user_str(),
 833                                     self.cmt_to_string(&err.cmt),
 834                                     self.loan_path_to_string(&lp))
 835                         }
 836                     }
 837                 };
 838
 839                 let mut db = match err.cause {
 840                     MutabilityViolation => {
 841                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 842                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 843                             let node_id = self.tcx.hir.hir_to_node_id(upvar_id.var_id);
 844                             let sp = self.tcx.hir.span(node_id);
 845                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 846                                                   environment for modifications";
 847                             match (self.tcx.sess.codemap().span_to_snippet(sp), &err.cmt.cat) {
 848                                 (_, &Categorization::Upvar(mc::Upvar {
 849                                     kind: ty::ClosureKind::Fn, ..
 850                                 })) => {
 851                                     db.note(fn_closure_msg);
 852                                     // we should point at the cause for this closure being
 853                                     // identified as `Fn` (like in signature of method this
 854                                     // closure was passed into)
 855                                 }
 856                                 (Ok(ref snippet), ref cat) => {
 857                                     let msg = &format!("consider making `{}` mutable", snippet);
 858                                     let suggestion = format!("mut {}", snippet);
 859
 860                                     if let &Categorization::Deref(ref cmt, _) = cat {
 861                                         if let Categorization::Upvar(mc::Upvar {
 862                                             kind: ty::ClosureKind::Fn, ..
 863                                         }) = cmt.cat {
 864                                             db.note(fn_closure_msg);
 865                                         } else {
 866                                             db.span_suggestion(sp, msg, suggestion);
 867                                         }
 868                                     } else {
 869                                         db.span_suggestion(sp, msg, suggestion);
 870                                     }
 871                                 }
 872                                 _ => {
 873                                     db.span_help(sp, "consider making this binding mutable");
 874                                 }
 875                             }
 876                         }
 877                         db
 878                     }
 879                     BorrowViolation(euv::ClosureCapture(_)) => {
 880                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 881                     }
 882                     BorrowViolation(euv::OverloadedOperator) |
 883                     BorrowViolation(euv::AddrOf) |
 884                     BorrowViolation(euv::RefBinding) |
 885                     BorrowViolation(euv::AutoRef) |
 886                     BorrowViolation(euv::AutoUnsafe) |
 887                     BorrowViolation(euv::ForLoop) |
 888                     BorrowViolation(euv::MatchDiscriminant) => {
 889                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 890                     }
 891                     BorrowViolation(euv::ClosureInvocation) => {
 892                         span_bug!(err.span,
 893                             "err_mutbl with a closure invocation");
 894                     }
 895                 };
 896
 897                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 898                 self.note_immutability_blame(&mut db, err.cmt.immutability_blame());
 899                 db.emit();
 900             }
 901             err_out_of_scope(super_scope, sub_scope, cause) => {
 902                 let msg = match opt_loan_path(&err.cmt) {
 903                     None => "borrowed value".to_string(),
 904                     Some(lp) => {
 905                         format!("`{}`", self.loan_path_to_string(&lp))
 906                     }
 907                 };
 908
 909                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 910                 let value_kind = match err.cmt.cat {
 911                     mc::Categorization::Rvalue(..) => "temporary value",
 912                     _ => "borrowed value",
 913                 };
 914
 915                 let is_closure = match cause {
 916                     euv::ClosureCapture(s) => {
 917                         // The primary span starts out as the closure creation point.
 918                         // Change the primary span here to highlight the use of the variable
 919                         // in the closure, because it seems more natural. Highlight
 920                         // closure creation point as a secondary span.
 921                         match db.span.primary_span() {
 922                             Some(primary) => {
 923                                 db.span = MultiSpan::from_span(s);
 924                                 db.span_label(primary, "capture occurs here");
 925                                 db.span_label(s, format!("{} does not live long enough",
 926                                                          value_kind));
 927                                 true
 928                             }
 929                             None => false
 930                         }
 931                     }
 932                     _ => {
 933                         db.span_label(error_span, format!("{} does not live long enough",
 934                                                           value_kind));
 935                         false
 936                     }
 937                 };
 938
 939                 let sub_span = self.region_end_span(sub_scope);
 940                 let super_span = self.region_end_span(super_scope);
 941
 942                 match (sub_span, super_span) {
 943                     (Some(s1), Some(s2)) if s1 == s2 => {
 944                         if !is_closure {
 945                             let msg = match opt_loan_path(&err.cmt) {
 946                                 None => value_kind.to_string(),
 947                                 Some(lp) => {
 948                                     format!("`{}`", self.loan_path_to_string(&lp))
 949                                 }
 950                             };
 951                             db.span_label(s1,
 952                                           format!("{} dropped here while still borrowed", msg));
 953                         } else {
 954                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 955                         }
 956                         db.note("values in a scope are dropped in the opposite order \
 957                                 they are created");
 958                     }
 959                     (Some(s1), Some(s2)) if !is_closure => {
 960                         let msg = match opt_loan_path(&err.cmt) {
 961                             None => value_kind.to_string(),
 962                             Some(lp) => {
 963                                 format!("`{}`", self.loan_path_to_string(&lp))
 964                             }
 965                         };
 966                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 967                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 968                     }
 969                     _ => {
 970                         match sub_span {
 971                             Some(s) => {
 972                                 db.span_label(s, format!("{} needs to live until here",
 973                                                           value_kind));
 974                             }
 975                             None => {
 976                                 self.tcx.note_and_explain_region(
 977                                     &self.region_scope_tree,
 978                                     &mut db,
 979                                     "borrowed value must be valid for ",
 980                                     sub_scope,
 981                                     "...");
 982                             }
 983                         }
 984                         match super_span {
 985                             Some(s) => {
 986                                 db.span_label(s, format!("{} only lives until here", value_kind));
 987                             }
 988                             None => {
 989                                 self.tcx.note_and_explain_region(
 990                                     &self.region_scope_tree,
 991                                     &mut db,
 992                                     "...but borrowed value is only valid for ",
 993                                     super_scope,
 994                                     "");
 995                             }
 996                         }
 997                     }
 998                 }
 999
1000                 if let ty::ReScope(scope) = *super_scope {
1001                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1002                     match self.tcx.hir.find(node_id) {
1003                         Some(hir_map::NodeStmt(_)) => {
1004                             db.note("consider using a `let` binding to increase its lifetime");
1005                         }
1006                         _ => {}
1007                     }
1008                 }
1009
1010                 db.emit();
1011             }
1012             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1013                 let descr = self.cmt_to_path_or_string(&err.cmt);
1014                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1015                 let descr = match opt_loan_path(&err.cmt) {
1016                     Some(lp) => {
1017                         format!("`{}`", self.loan_path_to_string(&lp))
1018                     }
1019                     None => self.cmt_to_string(&err.cmt),
1020                 };
1021                 self.tcx.note_and_explain_region(
1022                     &self.region_scope_tree,
1023                     &mut db,
1024                     &format!("{} would have to be valid for ",
1025                             descr),
1026                     loan_scope,
1027                     "...");
1028                 self.tcx.note_and_explain_region(
1029                     &self.region_scope_tree,
1030                     &mut db,
1031                     &format!("...but {} is only valid for ", descr),
1032                     ptr_scope,
1033                     "");
1034
1035                 db.emit();
1036             }
1037         }
1038     }
1039
1040     pub fn report_aliasability_violation(&self,
1041                                          span: Span,
1042                                          kind: AliasableViolationKind,
1043                                          cause: mc::AliasableReason,
1044                                          cmt: mc::cmt<'tcx>) {
1045         let mut is_closure = false;
1046         let prefix = match kind {
1047             MutabilityViolation => {
1048                 "cannot assign to data"
1049             }
1050             BorrowViolation(euv::ClosureCapture(_)) |
1051             BorrowViolation(euv::OverloadedOperator) |
1052             BorrowViolation(euv::AddrOf) |
1053             BorrowViolation(euv::AutoRef) |
1054             BorrowViolation(euv::AutoUnsafe) |
1055             BorrowViolation(euv::RefBinding) |
1056             BorrowViolation(euv::MatchDiscriminant) => {
1057                 "cannot borrow data mutably"
1058             }
1059
1060             BorrowViolation(euv::ClosureInvocation) => {
1061                 is_closure = true;
1062                 "closure invocation"
1063             }
1064
1065             BorrowViolation(euv::ForLoop) => {
1066                 "`for` loop"
1067             }
1068         };
1069
1070         match cause {
1071             mc::AliasableStaticMut => {
1072                 // This path cannot occur. `static mut X` is not checked
1073                 // for aliasability violations.
1074                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1075             }
1076             mc::AliasableStatic | mc::AliasableBorrowed => {}
1077         };
1078         let blame = cmt.immutability_blame();
1079         let mut err = match blame {
1080             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1081                 // FIXME: the distinction between these 2 messages looks wrong.
1082                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1083                     // The aliasability violation with closure captures can
1084                     // happen for nested closures, so we know the enclosing
1085                     // closure incorrectly accepts an `Fn` while it needs to
1086                     // be `FnMut`.
1087                     "consider changing this to accept closures that implement `FnMut`"
1088
1089                 } else {
1090                     "consider changing this closure to take self by mutable reference"
1091                 };
1092                 let node_id = self.tcx.hir.local_def_id_to_node_id(id);
1093                 let help_span = self.tcx.hir.span(node_id);
1094                 self.cannot_act_on_capture_in_sharable_fn(span,
1095                                                           prefix,
1096                                                           (help_span, help_msg),
1097                                                           Origin::Ast)
1098             }
1099             _ =>  {
1100                 self.cannot_assign_into_immutable_reference(span, prefix,
1101                                                             Origin::Ast)
1102             }
1103         };
1104         self.note_immutability_blame(&mut err, blame);
1105
1106         if is_closure {
1107             err.help("closures behind references must be called via `&mut`");
1108         }
1109         err.emit();
1110     }
1111
1112     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1113     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1114         // Check whether the argument is an immutable reference
1115         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1116         if let hir::TyRptr(lifetime, hir::MutTy {
1117             mutbl: hir::Mutability::MutImmutable,
1118             ref ty
1119         }) = pty.node {
1120             // Account for existing lifetimes when generating the message
1121             let pointee_snippet = match self.tcx.sess.codemap().span_to_snippet(ty.span) {
1122                 Ok(snippet) => snippet,
1123                 _ => return None
1124             };
1125
1126             let lifetime_snippet = if !lifetime.is_elided() {
1127                 format!("{} ", match self.tcx.sess.codemap().span_to_snippet(lifetime.span) {
1128                     Ok(lifetime_snippet) => lifetime_snippet,
1129                     _ => return None
1130                 })
1131             } else {
1132                 String::new()
1133             };
1134             Some(format!("use `&{}mut {}` here to make mutable",
1135                          lifetime_snippet,
1136                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1137         } else {
1138             None
1139         }
1140     }
1141
1142     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1143         let pat = match self.tcx.hir.get(node_id) {
1144             hir_map::Node::NodeBinding(pat) => pat,
1145             node => bug!("bad node for local: {:?}", node)
1146         };
1147
1148         match pat.node {
1149             hir::PatKind::Binding(..) => {
1150                 *self.tables
1151                      .pat_binding_modes()
1152                      .get(pat.hir_id)
1153                      .expect("missing binding mode")
1154             }
1155             _ => bug!("local is not a binding: {:?}", pat)
1156         }
1157     }
1158
1159     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1160         let parent = self.tcx.hir.get_parent_node(node_id);
1161         let parent_node = self.tcx.hir.get(parent);
1162
1163         // The parent node is like a fn
1164         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1165             // `nid`'s parent's `Body`
1166             let fn_body = self.tcx.hir.body(fn_like.body());
1167             // Get the position of `node_id` in the arguments list
1168             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1169             if let Some(i) = arg_pos {
1170                 // The argument's `Ty`
1171                 (Some(&fn_like.decl().inputs[i]),
1172                  i == 0 && fn_like.decl().has_implicit_self)
1173             } else {
1174                 (None, false)
1175             }
1176         } else {
1177             (None, false)
1178         }
1179     }
1180
1181     fn note_immutability_blame(&self,
1182                                db: &mut DiagnosticBuilder,
1183                                blame: Option<ImmutabilityBlame>) {
1184         match blame {
1185             None => {}
1186             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1187             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1188                 let let_span = self.tcx.hir.span(node_id);
1189                 if let ty::BindByValue(..) = self.local_binding_mode(node_id) {
1190                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(let_span) {
1191                         let (_, is_implicit_self) = self.local_ty(node_id);
1192                         if is_implicit_self && snippet != "self" {
1193                             // avoid suggesting `mut &self`.
1194                             return
1195                         }
1196                         db.span_label(
1197                             let_span,
1198                             format!("consider changing this to `mut {}`", snippet)
1199                         );
1200                     }
1201                 }
1202             }
1203             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1204                 let let_span = self.tcx.hir.span(node_id);
1205                 match self.local_binding_mode(node_id) {
1206                     ty::BindByReference(..) => {
1207                         let snippet = self.tcx.sess.codemap().span_to_snippet(let_span);
1208                         if let Ok(snippet) = snippet {
1209                             db.span_label(
1210                                 let_span,
1211                                 format!("consider changing this to `{}`",
1212                                          snippet.replace("ref ", "ref mut "))
1213                             );
1214                         }
1215                     }
1216                     ty::BindByValue(..) => {
1217                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1218                             if let Some(msg) =
1219                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1220                                 db.span_label(local_ty.span, msg);
1221                             }
1222                         }
1223                     }
1224                 }
1225             }
1226             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1227                 let node_id = match self.tcx.hir.as_local_node_id(field.did) {
1228                     Some(node_id) => node_id,
1229                     None => return
1230                 };
1231
1232                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(node_id) {
1233                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1234                         db.span_label(field.ty.span, msg);
1235                     }
1236                 }
1237             }
1238         }
1239     }
1240
1241     fn report_out_of_scope_escaping_closure_capture(&self,
1242                                                     err: &BckError<'tcx>,
1243                                                     capture_span: Span)
1244     {
1245         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1246
1247         let suggestion =
1248             match self.tcx.sess.codemap().span_to_snippet(err.span) {
1249                 Ok(string) => format!("move {}", string),
1250                 Err(_) => format!("move |<args>| <body>")
1251             };
1252
1253         self.cannot_capture_in_long_lived_closure(err.span,
1254                                                   &cmt_path_or_string,
1255                                                   capture_span,
1256                                                   Origin::Ast)
1257             .span_suggestion(err.span,
1258                              &format!("to force the closure to take ownership of {} \
1259                                        (and any other referenced variables), \
1260                                        use the `move` keyword",
1261                                        cmt_path_or_string),
1262                              suggestion)
1263             .emit();
1264     }
1265
1266     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1267         match *region {
1268             ty::ReScope(scope) => {
1269                 Some(self.tcx.sess.codemap().end_point(
1270                         scope.span(self.tcx, &self.region_scope_tree)))
1271             }
1272             _ => None
1273         }
1274     }
1275
1276     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1277                                     error_span: &Span) {
1278         match err.cmt.note {
1279             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1280                 // If this is an `Fn` closure, it simply can't mutate upvars.
1281                 // If it's an `FnMut` closure, the original variable was declared immutable.
1282                 // We need to determine which is the case here.
1283                 let kind = match err.cmt.upvar().unwrap().cat {
1284                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1285                     _ => bug!()
1286                 };
1287                 if kind == ty::ClosureKind::Fn {
1288                     let closure_node_id =
1289                         self.tcx.hir.local_def_id_to_node_id(upvar_id.closure_expr_id);
1290                     db.span_help(self.tcx.hir.span(closure_node_id),
1291                                  "consider changing this closure to take \
1292                                   self by mutable reference");
1293                 }
1294             }
1295             _ => {
1296                 if let Categorization::Deref(..) = err.cmt.cat {
1297                     db.span_label(*error_span, "cannot borrow as mutable");
1298                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1299                     let span = self.tcx.hir.span(local_id);
1300                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1301                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1302                             db.span_label(*error_span, "cannot reborrow mutably");
1303                             db.span_label(*error_span, "try removing `&mut` here");
1304                         } else {
1305                             db.span_label(*error_span, "cannot borrow mutably");
1306                         }
1307                     } else {
1308                         db.span_label(*error_span, "cannot borrow mutably");
1309                     }
1310                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1311                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1312                         db.span_label(*error_span,
1313                                       "cannot mutably borrow field of immutable binding");
1314                     }
1315                 }
1316             }
1317         }
1318     }
1319     pub fn append_loan_path_to_string(&self,
1320                                       loan_path: &LoanPath<'tcx>,
1321                                       out: &mut String) {
1322         match loan_path.kind {
1323             LpUpvar(ty::UpvarId { var_id: id, closure_expr_id: _ }) => {
1324                 out.push_str(&self.tcx.hir.name(self.tcx.hir.hir_to_node_id(id)).as_str());
1325             }
1326             LpVar(id) => {
1327                 out.push_str(&self.tcx.hir.name(id).as_str());
1328             }
1329
1330             LpDowncast(ref lp_base, variant_def_id) => {
1331                 out.push('(');
1332                 self.append_loan_path_to_string(&lp_base, out);
1333                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1334                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1335                 out.push(')');
1336             }
1337
1338             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1339                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1340                 match fname {
1341                     mc::NamedField(fname) => {
1342                         out.push('.');
1343                         out.push_str(&fname.as_str());
1344                     }
1345                     mc::PositionalField(idx) => {
1346                         out.push('.');
1347                         out.push_str(&idx.to_string());
1348                     }
1349                 }
1350             }
1351
1352             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1353                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1354                 out.push_str("[..]");
1355             }
1356
1357             LpExtend(ref lp_base, _, LpDeref(_)) => {
1358                 out.push('*');
1359                 self.append_loan_path_to_string(&lp_base, out);
1360             }
1361         }
1362     }
1363
1364     pub fn append_autoderefd_loan_path_to_string(&self,
1365                                                  loan_path: &LoanPath<'tcx>,
1366                                                  out: &mut String) {
1367         match loan_path.kind {
1368             LpExtend(ref lp_base, _, LpDeref(_)) => {
1369                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1370                 // rules would normally allow users to omit the `*x`.
1371                 // So just serialize such paths to `x.f` or x[3]` respectively.
1372                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1373             }
1374
1375             LpDowncast(ref lp_base, variant_def_id) => {
1376                 out.push('(');
1377                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1378                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1379                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1380                 out.push(')');
1381             }
1382
1383             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1384                 self.append_loan_path_to_string(loan_path, out)
1385             }
1386         }
1387     }
1388
1389     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1390         let mut result = String::new();
1391         self.append_loan_path_to_string(loan_path, &mut result);
1392         result
1393     }
1394
1395     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1396         cmt.descriptive_string(self.tcx)
1397     }
1398
1399     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1400         match opt_loan_path(cmt) {
1401             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1402             None => self.cmt_to_string(cmt),
1403         }
1404     }
1405 }
1406
1407 impl BitwiseOperator for LoanDataFlowOperator {
1408     #[inline]
1409     fn join(&self, succ: usize, pred: usize) -> usize {
1410         succ | pred // loans from both preds are in scope
1411     }
1412 }
1413
1414 impl DataFlowOperator for LoanDataFlowOperator {
1415     #[inline]
1416     fn initial_value(&self) -> bool {
1417         false // no loans in scope by default
1418     }
1419 }
1420
1421 impl<'tcx> fmt::Debug for InteriorKind {
1422     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1423         match *self {
1424             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1425             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1426             InteriorElement => write!(f, "[]"),
1427         }
1428     }
1429 }
1430
1431 impl<'tcx> fmt::Debug for Loan<'tcx> {
1432     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1433         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1434                self.index,
1435                self.loan_path,
1436                self.kind,
1437                self.gen_scope,
1438                self.kill_scope,
1439                self.restricted_paths)
1440     }
1441 }
1442
1443 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1444     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1445         match self.kind {
1446             LpVar(id) => {
1447                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1448             }
1449
1450             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1451                 let s = ty::tls::with(|tcx| {
1452                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1453                     tcx.hir.node_to_string(var_node_id)
1454                 });
1455                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1456             }
1457
1458             LpDowncast(ref lp, variant_def_id) => {
1459                 let variant_str = if variant_def_id.is_local() {
1460                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1461                 } else {
1462                     format!("{:?}", variant_def_id)
1463                 };
1464                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1465             }
1466
1467             LpExtend(ref lp, _, LpDeref(_)) => {
1468                 write!(f, "{:?}.*", lp)
1469             }
1470
1471             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1472                 write!(f, "{:?}.{:?}", lp, interior)
1473             }
1474         }
1475     }
1476 }
1477
1478 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1479     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1480         match self.kind {
1481             LpVar(id) => {
1482                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1483             }
1484
1485             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1486                 let s = ty::tls::with(|tcx| {
1487                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1488                     tcx.hir.node_to_string(var_node_id)
1489                 });
1490                 write!(f, "$({} captured by closure)", s)
1491             }
1492
1493             LpDowncast(ref lp, variant_def_id) => {
1494                 let variant_str = if variant_def_id.is_local() {
1495                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1496                 } else {
1497                     format!("{:?}", variant_def_id)
1498                 };
1499                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1500             }
1501
1502             LpExtend(ref lp, _, LpDeref(_)) => {
1503                 write!(f, "{}.*", lp)
1504             }
1505
1506             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1507                 write!(f, "{}.{:?}", lp, interior)
1508             }
1509         }
1510     }
1511 }