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