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::query::Providers;
  41 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  42 use rustc_mir::util::suggest_ref_mut;
  43 use rustc::util::nodemap::FxHashSet;
  44
  45 use std::cell::RefCell;
  46 use std::fmt;
  47 use std::rc::Rc;
  48 use rustc_data_structures::sync::Lrc;
  49 use std::hash::{Hash, Hasher};
  50 use syntax::ast;
  51 use syntax_pos::{MultiSpan, Span};
  52 use errors::{DiagnosticBuilder, DiagnosticId};
  53
  54 use rustc::hir;
  55 use rustc::hir::intravisit::{self, Visitor};
  56
  57 pub mod check_loans;
  58
  59 pub mod gather_loans;
  60
  61 pub mod move_data;
  62
  63 mod unused;
  64
  65 #[derive(Clone, Copy)]
  66 pub struct LoanDataFlowOperator;
  67
  68 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  69
  70 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  71     tcx.par_body_owners(|body_owner_def_id| {
  72         tcx.borrowck(body_owner_def_id);
  73     });
  74 }
  75
  76 pub fn provide(providers: &mut Providers) {
  77     *providers = Providers {
  78         borrowck,
  79         ..*providers
  80     };
  81 }
  82
  83 /// Collection of conclusions determined via borrow checker analyses.
  84 pub struct AnalysisData<'a, 'tcx: 'a> {
  85     pub all_loans: Vec<Loan<'tcx>>,
  86     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  87     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  88 }
  89
  90 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  91     -> Lrc<BorrowCheckResult>
  92 {
  93     assert!(tcx.use_ast_borrowck());
  94
  95     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  96
  97     let owner_id = tcx.hir.as_local_node_id(owner_def_id).unwrap();
  98
  99     match tcx.hir.get(owner_id) {
 100         hir_map::NodeStructCtor(_) |
 101         hir_map::NodeVariant(_) => {
 102             // We get invoked with anything that has MIR, but some of
 103             // those things (notably the synthesized constructors from
 104             // tuple structs/variants) do not have an associated body
 105             // and do not need borrowchecking.
 106             return Lrc::new(BorrowCheckResult {
 107                 used_mut_nodes: FxHashSet(),
 108             })
 109         }
 110         _ => { }
 111     }
 112
 113     let body_id = tcx.hir.body_owned_by(owner_id);
 114     let tables = tcx.typeck_tables_of(owner_def_id);
 115     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 116     let body = tcx.hir.body(body_id);
 117     let mut bccx = BorrowckCtxt {
 118         tcx,
 119         tables,
 120         region_scope_tree,
 121         owner_def_id,
 122         body,
 123         used_mut_nodes: RefCell::new(FxHashSet()),
 124     };
 125
 126     // Eventually, borrowck will always read the MIR, but at the
 127     // moment we do not. So, for now, we always force MIR to be
 128     // constructed for a given fn, since this may result in errors
 129     // being reported and we want that to happen.
 130     //
 131     // Note that `mir_validated` is a "stealable" result; the
 132     // thief, `optimized_mir()`, forces borrowck, so we know that
 133     // is not yet stolen.
 134     ty::query::queries::mir_validated::ensure(tcx, owner_def_id);
 135
 136     // option dance because you can't capture an uninitialized variable
 137     // by mut-ref.
 138     let mut cfg = None;
 139     if let Some(AnalysisData { all_loans,
 140                                loans: loan_dfcx,
 141                                move_data: flowed_moves }) =
 142         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 143                                      |bccx| {
 144                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 145                                          cfg.as_mut().unwrap()
 146                                      })
 147     {
 148         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 149     }
 150
 151     if !tcx.use_mir_borrowck() {
 152         unused::check(&mut bccx, body);
 153     }
 154
 155     Lrc::new(BorrowCheckResult {
 156         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 157     })
 158 }
 159
 160 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 161                                                  force_analysis: bool,
 162                                                  body_id: hir::BodyId,
 163                                                  get_cfg: F)
 164                                                  -> Option<AnalysisData<'a, 'tcx>>
 165     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 166 {
 167     // Check the body of fn items.
 168     let tcx = this.tcx;
 169     let id_range = {
 170         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 171         visitor.visit_body(this.body);
 172         visitor.result()
 173     };
 174     let (all_loans, move_data) =
 175         gather_loans::gather_loans_in_fn(this, body_id);
 176
 177     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 178         // large arrays of data inserted as constants can take a lot of
 179         // time and memory to borrow-check - see issue #36799. However,
 180         // they don't have places, so no borrow-check is actually needed.
 181         // Recognize that case and skip borrow-checking.
 182         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 183         return None;
 184     } else {
 185         debug!("propagating loans in {:?}", body_id);
 186     }
 187
 188     let cfg = get_cfg(this);
 189     let mut loan_dfcx =
 190         DataFlowContext::new(this.tcx,
 191                              "borrowck",
 192                              Some(this.body),
 193                              cfg,
 194                              LoanDataFlowOperator,
 195                              id_range,
 196                              all_loans.len());
 197     for (loan_idx, loan) in all_loans.iter().enumerate() {
 198         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 199         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 200                            loan.kill_scope.item_local_id(),
 201                            loan_idx);
 202     }
 203     loan_dfcx.add_kills_from_flow_exits(cfg);
 204     loan_dfcx.propagate(cfg, this.body);
 205
 206     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 207                                                       this,
 208                                                       cfg,
 209                                                       id_range,
 210                                                       this.body);
 211
 212     Some(AnalysisData { all_loans,
 213                         loans: loan_dfcx,
 214                         move_data:flowed_moves })
 215 }
 216
 217 /// Accessor for introspective clients inspecting `AnalysisData` and
 218 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 219 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 220     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 221     body_id: hir::BodyId,
 222     cfg: &cfg::CFG)
 223     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 224 {
 225     let owner_id = tcx.hir.body_owner(body_id);
 226     let owner_def_id = tcx.hir.local_def_id(owner_id);
 227     let tables = tcx.typeck_tables_of(owner_def_id);
 228     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 229     let body = tcx.hir.body(body_id);
 230     let mut bccx = BorrowckCtxt {
 231         tcx,
 232         tables,
 233         region_scope_tree,
 234         owner_def_id,
 235         body,
 236         used_mut_nodes: RefCell::new(FxHashSet()),
 237     };
 238
 239     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 240     (bccx, dataflow_data.unwrap())
 241 }
 242
 243 // ----------------------------------------------------------------------
 244 // Type definitions
 245
 246 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 247     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 248
 249     // tables for the current thing we are checking; set to
 250     // Some in `borrowck_fn` and cleared later
 251     tables: &'a ty::TypeckTables<'tcx>,
 252
 253     region_scope_tree: Lrc<region::ScopeTree>,
 254
 255     owner_def_id: DefId,
 256
 257     body: &'tcx hir::Body,
 258
 259     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 260 }
 261
 262 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 263     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 264                                                      sp: S,
 265                                                      msg: &str,
 266                                                      code: DiagnosticId)
 267                                                      -> DiagnosticBuilder<'a>
 268     {
 269         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 270     }
 271
 272     fn struct_span_err<S: Into<MultiSpan>>(self,
 273                                            sp: S,
 274                                            msg: &str)
 275                                            -> DiagnosticBuilder<'a>
 276     {
 277         self.tcx.sess.struct_span_err(sp, msg)
 278     }
 279
 280     fn cancel_if_wrong_origin(self,
 281                               mut diag: DiagnosticBuilder<'a>,
 282                               o: Origin)
 283                               -> DiagnosticBuilder<'a>
 284     {
 285         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 286             self.tcx.sess.diagnostic().cancel(&mut diag);
 287         }
 288         diag
 289     }
 290 }
 291
 292 ///////////////////////////////////////////////////////////////////////////
 293 // Loans and loan paths
 294
 295 /// Record of a loan that was issued.
 296 pub struct Loan<'tcx> {
 297     index: usize,
 298     loan_path: Rc<LoanPath<'tcx>>,
 299     kind: ty::BorrowKind,
 300     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 301
 302     /// gen_scope indicates where loan is introduced. Typically the
 303     /// loan is introduced at the point of the borrow, but in some
 304     /// cases, notably method arguments, the loan may be introduced
 305     /// only later, once it comes into scope.  See also
 306     /// `GatherLoanCtxt::compute_gen_scope`.
 307     gen_scope: region::Scope,
 308
 309     /// kill_scope indicates when the loan goes out of scope.  This is
 310     /// either when the lifetime expires or when the local variable
 311     /// which roots the loan-path goes out of scope, whichever happens
 312     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 313     kill_scope: region::Scope,
 314     span: Span,
 315     cause: euv::LoanCause,
 316 }
 317
 318 impl<'tcx> Loan<'tcx> {
 319     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 320         self.loan_path.clone()
 321     }
 322 }
 323
 324 #[derive(Eq)]
 325 pub struct LoanPath<'tcx> {
 326     kind: LoanPathKind<'tcx>,
 327     ty: Ty<'tcx>,
 328 }
 329
 330 impl<'tcx> PartialEq for LoanPath<'tcx> {
 331     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 332         self.kind == that.kind
 333     }
 334 }
 335
 336 impl<'tcx> Hash for LoanPath<'tcx> {
 337     fn hash<H: Hasher>(&self, state: &mut H) {
 338         self.kind.hash(state);
 339     }
 340 }
 341
 342 #[derive(PartialEq, Eq, Hash, Debug)]
 343 pub enum LoanPathKind<'tcx> {
 344     LpVar(ast::NodeId),                         // `x` in README.md
 345     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 346     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 347     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 348 }
 349
 350 impl<'tcx> LoanPath<'tcx> {
 351     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 352         LoanPath { kind: kind, ty: ty }
 353     }
 354
 355     fn to_type(&self) -> Ty<'tcx> { self.ty }
 356
 357     fn has_downcast(&self) -> bool {
 358         match self.kind {
 359             LpDowncast(_, _) => true,
 360             LpExtend(ref lp, _, LpInterior(_, _)) => {
 361                 lp.has_downcast()
 362             }
 363             _ => false,
 364         }
 365     }
 366 }
 367
 368 // FIXME (pnkfelix): See discussion here
 369 // https://github.com/pnkfelix/rust/commit/
 370 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 371 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 372
 373 // A local, "cleaned" version of `mc::InteriorKind` that drops
 374 // information that is not relevant to loan-path analysis. (In
 375 // particular, the distinction between how precisely an array-element
 376 // is tracked is irrelevant here.)
 377 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 378 pub enum InteriorKind {
 379     InteriorField(mc::FieldIndex),
 380     InteriorElement,
 381 }
 382
 383 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 384 impl ToInteriorKind for mc::InteriorKind {
 385     fn cleaned(self) -> InteriorKind {
 386         match self {
 387             mc::InteriorField(name) => InteriorField(name),
 388             mc::InteriorElement(_) => InteriorElement,
 389         }
 390     }
 391 }
 392
 393 // This can be:
 394 // - a pointer dereference (`*P` in README.md)
 395 // - a field reference, with an optional definition of the containing
 396 //   enum variant (`P.f` in README.md)
 397 // `DefId` is present when the field is part of struct that is in
 398 // a variant of an enum. For instance in:
 399 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 400 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 401 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 402 pub enum LoanPathElem<'tcx> {
 403     LpDeref(mc::PointerKind<'tcx>),
 404     LpInterior(Option<DefId>, InteriorKind),
 405 }
 406
 407 fn closure_to_block(closure_id: LocalDefId,
 408                     tcx: TyCtxt) -> ast::NodeId {
 409     let closure_id = tcx.hir.local_def_id_to_node_id(closure_id);
 410     match tcx.hir.get(closure_id) {
 411         hir_map::NodeExpr(expr) => match expr.node {
 412             hir::ExprKind::Closure(.., body_id, _, _) => {
 413                 body_id.node_id
 414             }
 415             _ => {
 416                 bug!("encountered non-closure id: {}", closure_id)
 417             }
 418         },
 419         _ => bug!("encountered non-expr id: {}", closure_id)
 420     }
 421 }
 422
 423 impl<'a, 'tcx> LoanPath<'tcx> {
 424     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 425         match self.kind {
 426             LpVar(local_id) => {
 427                 let hir_id = bccx.tcx.hir.node_to_hir_id(local_id);
 428                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 429             }
 430             LpUpvar(upvar_id) => {
 431                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 432                 let hir_id = bccx.tcx.hir.node_to_hir_id(block_id);
 433                 region::Scope::Node(hir_id.local_id)
 434             }
 435             LpDowncast(ref base, _) |
 436             LpExtend(ref base, ..) => base.kill_scope(bccx),
 437         }
 438     }
 439
 440     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 441         match (&self.kind, &other.kind) {
 442             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 443              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 444                 if id == id2 && opt_variant_id == opt_variant_id2 {
 445                     base.has_fork(&base2)
 446                 } else {
 447                     true
 448                 },
 449             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 450             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 451             _ => false,
 452         }
 453     }
 454
 455     fn depth(&self) -> usize {
 456         match self.kind {
 457             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 458             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 459             _ => 0,
 460         }
 461     }
 462
 463     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 464         match (&self.kind, &other.kind) {
 465             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 466              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 467                 if id == id2 && opt_variant_id == opt_variant_id2 {
 468                     base.common(&base2).map(|x| {
 469                         let xd = x.depth();
 470                         if base.depth() == xd && base2.depth() == xd {
 471                             LoanPath {
 472                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 473                                 ty: self.ty,
 474                             }
 475                         } else {
 476                             x
 477                         }
 478                     })
 479                 } else {
 480                     base.common(&base2)
 481                 }
 482             }
 483             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 484             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 485             (&LpVar(id), &LpVar(id2)) => {
 486                 if id == id2 {
 487                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 488                 } else {
 489                     None
 490                 }
 491             }
 492             (&LpUpvar(id), &LpUpvar(id2)) => {
 493                 if id == id2 {
 494                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 495                 } else {
 496                     None
 497                 }
 498             }
 499             _ => None,
 500         }
 501     }
 502 }
 503
 504 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 505 // mutable independently of the struct it belongs to. (#35937)
 506 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 507     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 508
 509     match cmt.cat {
 510         Categorization::Rvalue(..) |
 511         Categorization::StaticItem => {
 512             (None, false)
 513         }
 514
 515         Categorization::Local(id) => {
 516             (Some(new_lp(LpVar(id))), false)
 517         }
 518
 519         Categorization::Upvar(mc::Upvar { id, .. }) => {
 520             (Some(new_lp(LpUpvar(id))), false)
 521         }
 522
 523         Categorization::Deref(ref cmt_base, pk) => {
 524             let lp = opt_loan_path_is_field(cmt_base);
 525             (lp.0.map(|lp| {
 526                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 527             }), lp.1)
 528         }
 529
 530         Categorization::Interior(ref cmt_base, ik) => {
 531             (opt_loan_path(cmt_base).map(|lp| {
 532                 let opt_variant_id = match cmt_base.cat {
 533                     Categorization::Downcast(_, did) =>  Some(did),
 534                     _ => None
 535                 };
 536                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 537             }), true)
 538         }
 539
 540         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 541             let lp = opt_loan_path_is_field(cmt_base);
 542             (lp.0.map(|lp| {
 543                 new_lp(LpDowncast(lp, variant_def_id))
 544             }), lp.1)
 545         }
 546     }
 547 }
 548
 549 /// Computes the `LoanPath` (if any) for a `cmt`.
 550 /// Note that this logic is somewhat duplicated in
 551 /// the method `compute()` found in `gather_loans::restrictions`,
 552 /// which allows it to share common loan path pieces as it
 553 /// traverses the CMT.
 554 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 555     opt_loan_path_is_field(cmt).0
 556 }
 557
 558 ///////////////////////////////////////////////////////////////////////////
 559 // Errors
 560
 561 // Errors that can occur
 562 #[derive(Debug, PartialEq)]
 563 pub enum bckerr_code<'tcx> {
 564     err_mutbl,
 565     /// superscope, subscope, loan cause
 566     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 567     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 568 }
 569
 570 // Combination of an error code and the categorization of the expression
 571 // that caused it
 572 #[derive(Debug, PartialEq)]
 573 pub struct BckError<'c, 'tcx: 'c> {
 574     span: Span,
 575     cause: AliasableViolationKind,
 576     cmt: &'c mc::cmt_<'tcx>,
 577     code: bckerr_code<'tcx>
 578 }
 579
 580 #[derive(Copy, Clone, Debug, PartialEq)]
 581 pub enum AliasableViolationKind {
 582     MutabilityViolation,
 583     BorrowViolation(euv::LoanCause)
 584 }
 585
 586 #[derive(Copy, Clone, Debug)]
 587 pub enum MovedValueUseKind {
 588     MovedInUse,
 589     MovedInCapture,
 590 }
 591
 592 ///////////////////////////////////////////////////////////////////////////
 593 // Misc
 594
 595 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 596     pub fn is_subregion_of(&self,
 597                            r_sub: ty::Region<'tcx>,
 598                            r_sup: ty::Region<'tcx>)
 599                            -> bool
 600     {
 601         let region_rels = RegionRelations::new(self.tcx,
 602                                                self.owner_def_id,
 603                                                &self.region_scope_tree,
 604                                                &self.tables.free_region_map);
 605         region_rels.is_subregion_of(r_sub, r_sup)
 606     }
 607
 608     pub fn report(&self, err: BckError<'a, 'tcx>) {
 609         // Catch and handle some particular cases.
 610         match (&err.code, &err.cause) {
 611             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 612              &BorrowViolation(euv::ClosureCapture(span))) |
 613             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 614              &BorrowViolation(euv::ClosureCapture(span))) |
 615             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 616              &BorrowViolation(euv::ClosureCapture(span))) => {
 617                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 618             }
 619             _ => { }
 620         }
 621
 622         self.report_bckerr(&err);
 623     }
 624
 625     pub fn report_use_of_moved_value(&self,
 626                                      use_span: Span,
 627                                      use_kind: MovedValueUseKind,
 628                                      lp: &LoanPath<'tcx>,
 629                                      the_move: &move_data::Move,
 630                                      moved_lp: &LoanPath<'tcx>,
 631                                      _param_env: ty::ParamEnv<'tcx>) {
 632         let (verb, verb_participle) = match use_kind {
 633             MovedInUse => ("use", "used"),
 634             MovedInCapture => ("capture", "captured"),
 635         };
 636
 637         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 638             move_data::Declared => {
 639                 // If this is an uninitialized variable, just emit a simple warning
 640                 // and return.
 641                 self.cannot_act_on_uninitialized_variable(use_span,
 642                                                           verb,
 643                                                           &self.loan_path_to_string(lp),
 644                                                           Origin::Ast)
 645                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 646                                                   self.loan_path_to_string(lp)))
 647                     .emit();
 648                 return;
 649             }
 650             _ => {
 651                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 652                 // normally generate a rather confusing message:
 653                 //
 654                 //     error: use of moved value: `x.b`
 655                 //     note: `x.a` moved here...
 656                 //
 657                 // What we want to do instead is get the 'common ancestor' of the two moves and
 658                 // use that for most of the message instead, giving is something like this:
 659                 //
 660                 //     error: use of moved value: `x`
 661                 //     note: `x` moved here (through moving `x.a`)...
 662
 663                 let common = moved_lp.common(lp);
 664                 let has_common = common.is_some();
 665                 let has_fork = moved_lp.has_fork(lp);
 666                 let (nl, ol, moved_lp_msg) =
 667                     if has_fork && has_common {
 668                         let nl = self.loan_path_to_string(&common.unwrap());
 669                         let ol = nl.clone();
 670                         let moved_lp_msg = format!(" (through moving `{}`)",
 671                                                    self.loan_path_to_string(moved_lp));
 672                         (nl, ol, moved_lp_msg)
 673                     } else {
 674                         (self.loan_path_to_string(lp),
 675                          self.loan_path_to_string(moved_lp),
 676                          String::new())
 677                     };
 678
 679                 let partial = moved_lp.depth() > lp.depth();
 680                 let msg = if !has_fork && partial { "partially " }
 681                           else if has_fork && !has_common { "collaterally "}
 682                 else { "" };
 683                 let mut err = self.cannot_act_on_moved_value(use_span,
 684                                                              verb,
 685                                                              msg,
 686                                                              Some(format!("{}", nl)),
 687                                                              Origin::Ast);
 688                 let need_note = match lp.ty.sty {
 689                     ty::TypeVariants::TyClosure(id, _) => {
 690                         let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
 691                         let hir_id = self.tcx.hir.node_to_hir_id(node_id);
 692                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 693                             err.span_note(*span, &format!(
 694                                 "closure cannot be invoked more than once because \
 695                                 it moves the variable `{}` out of its environment",
 696                                 name
 697                             ));
 698                             false
 699                         } else {
 700                             true
 701                         }
 702                     }
 703                     _ => true,
 704                 };
 705                 (ol, moved_lp_msg, err, need_note)
 706             }
 707         };
 708
 709         // Get type of value and span where it was previously
 710         // moved.
 711         let node_id = self.tcx.hir.hir_to_node_id(hir::HirId {
 712             owner: self.body.value.hir_id.owner,
 713             local_id: the_move.id
 714         });
 715         let (move_span, move_note) = match the_move.kind {
 716             move_data::Declared => {
 717                 unreachable!();
 718             }
 719
 720             move_data::MoveExpr |
 721             move_data::MovePat => (self.tcx.hir.span(node_id), ""),
 722
 723             move_data::Captured =>
 724                 (match self.tcx.hir.expect_expr(node_id).node {
 725                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 726                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 727                                   the_move.id, r),
 728                 }, " (into closure)"),
 729         };
 730
 731         // Annotate the use and the move in the span. Watch out for
 732         // the case where the use and the move are the same. This
 733         // means the use is in a loop.
 734         err = if use_span == move_span {
 735             err.span_label(
 736                 use_span,
 737                 format!("value moved{} here in previous iteration of loop",
 738                          move_note));
 739             err
 740         } else {
 741             err.span_label(use_span, format!("value {} here after move", verb_participle));
 742             err.span_label(move_span, format!("value moved{} here", move_note));
 743             err
 744         };
 745
 746         if need_note {
 747             err.note(&format!(
 748                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 749                 if moved_lp.has_downcast() {
 750                     "the value".to_string()
 751                 } else {
 752                     format!("`{}`", self.loan_path_to_string(moved_lp))
 753                 },
 754                 moved_lp.ty));
 755         }
 756
 757         // Note: we used to suggest adding a `ref binding` or calling
 758         // `clone` but those suggestions have been removed because
 759         // they are often not what you actually want to do, and were
 760         // not considered particularly helpful.
 761
 762         err.emit();
 763     }
 764
 765     pub fn report_partial_reinitialization_of_uninitialized_structure(
 766             &self,
 767             span: Span,
 768             lp: &LoanPath<'tcx>) {
 769         self.cannot_partially_reinit_an_uninit_struct(span,
 770                                                       &self.loan_path_to_string(lp),
 771                                                       Origin::Ast)
 772             .emit();
 773     }
 774
 775     pub fn report_reassigned_immutable_variable(&self,
 776                                                 span: Span,
 777                                                 lp: &LoanPath<'tcx>,
 778                                                 assign:
 779                                                 &move_data::Assignment) {
 780         let mut err = self.cannot_reassign_immutable(span,
 781                                                      &self.loan_path_to_string(lp),
 782                                                      false,
 783                                                      Origin::Ast);
 784         err.span_label(span, "cannot assign twice to immutable variable");
 785         if span != assign.span {
 786             err.span_label(assign.span, format!("first assignment to `{}`",
 787                                                 self.loan_path_to_string(lp)));
 788         }
 789         err.emit();
 790     }
 791
 792     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 793                                                          s: S,
 794                                                          msg: &str,
 795                                                          code: DiagnosticId)
 796                                                          -> DiagnosticBuilder<'a> {
 797         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 798     }
 799
 800     pub fn span_err_with_code<S: Into<MultiSpan>>(
 801         &self,
 802         s: S,
 803         msg: &str,
 804         code: DiagnosticId,
 805     ) {
 806         self.tcx.sess.span_err_with_code(s, msg, code);
 807     }
 808
 809     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 810         let error_span = err.span.clone();
 811
 812         match err.code {
 813             err_mutbl => {
 814                 let descr = match err.cmt.note {
 815                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 816                         self.cmt_to_string(&err.cmt)
 817                     }
 818                     _ => match opt_loan_path_is_field(&err.cmt) {
 819                         (None, true) => {
 820                             format!("{} of {} binding",
 821                                     self.cmt_to_string(&err.cmt),
 822                                     err.cmt.mutbl.to_user_str())
 823
 824                         }
 825                         (None, false) => {
 826                             format!("{} {}",
 827                                     err.cmt.mutbl.to_user_str(),
 828                                     self.cmt_to_string(&err.cmt))
 829
 830                         }
 831                         (Some(lp), true) => {
 832                             format!("{} `{}` of {} binding",
 833                                     self.cmt_to_string(&err.cmt),
 834                                     self.loan_path_to_string(&lp),
 835                                     err.cmt.mutbl.to_user_str())
 836                         }
 837                         (Some(lp), false) => {
 838                             format!("{} {} `{}`",
 839                                     err.cmt.mutbl.to_user_str(),
 840                                     self.cmt_to_string(&err.cmt),
 841                                     self.loan_path_to_string(&lp))
 842                         }
 843                     }
 844                 };
 845
 846                 let mut db = match err.cause {
 847                     MutabilityViolation => {
 848                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 849                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 850                             let node_id = self.tcx.hir.hir_to_node_id(upvar_id.var_id);
 851                             let sp = self.tcx.hir.span(node_id);
 852                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 853                                                   environment for modifications";
 854                             match (self.tcx.sess.codemap().span_to_snippet(sp), &err.cmt.cat) {
 855                                 (_, &Categorization::Upvar(mc::Upvar {
 856                                     kind: ty::ClosureKind::Fn, ..
 857                                 })) => {
 858                                     db.note(fn_closure_msg);
 859                                     // we should point at the cause for this closure being
 860                                     // identified as `Fn` (like in signature of method this
 861                                     // closure was passed into)
 862                                 }
 863                                 (Ok(ref snippet), ref cat) => {
 864                                     let msg = &format!("consider making `{}` mutable", snippet);
 865                                     let suggestion = format!("mut {}", snippet);
 866
 867                                     if let &Categorization::Deref(ref cmt, _) = cat {
 868                                         if let Categorization::Upvar(mc::Upvar {
 869                                             kind: ty::ClosureKind::Fn, ..
 870                                         }) = cmt.cat {
 871                                             db.note(fn_closure_msg);
 872                                         } else {
 873                                             db.span_suggestion(sp, msg, suggestion);
 874                                         }
 875                                     } else {
 876                                         db.span_suggestion(sp, msg, suggestion);
 877                                     }
 878                                 }
 879                                 _ => {
 880                                     db.span_help(sp, "consider making this binding mutable");
 881                                 }
 882                             }
 883                         }
 884                         db
 885                     }
 886                     BorrowViolation(euv::ClosureCapture(_)) => {
 887                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 888                     }
 889                     BorrowViolation(euv::OverloadedOperator) |
 890                     BorrowViolation(euv::AddrOf) |
 891                     BorrowViolation(euv::RefBinding) |
 892                     BorrowViolation(euv::AutoRef) |
 893                     BorrowViolation(euv::AutoUnsafe) |
 894                     BorrowViolation(euv::ForLoop) |
 895                     BorrowViolation(euv::MatchDiscriminant) => {
 896                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 897                     }
 898                     BorrowViolation(euv::ClosureInvocation) => {
 899                         span_bug!(err.span,
 900                             "err_mutbl with a closure invocation");
 901                     }
 902                 };
 903
 904                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 905                 self.note_immutability_blame(
 906                     &mut db,
 907                     err.cmt.immutability_blame(),
 908                     self.tcx.hir.hir_to_node_id(err.cmt.hir_id)
 909                 );
 910                 db.emit();
 911             }
 912             err_out_of_scope(super_scope, sub_scope, cause) => {
 913                 let msg = match opt_loan_path(&err.cmt) {
 914                     None => "borrowed value".to_string(),
 915                     Some(lp) => {
 916                         format!("`{}`", self.loan_path_to_string(&lp))
 917                     }
 918                 };
 919
 920                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 921                 let value_kind = match err.cmt.cat {
 922                     mc::Categorization::Rvalue(..) => "temporary value",
 923                     _ => "borrowed value",
 924                 };
 925
 926                 let is_closure = match cause {
 927                     euv::ClosureCapture(s) => {
 928                         // The primary span starts out as the closure creation point.
 929                         // Change the primary span here to highlight the use of the variable
 930                         // in the closure, because it seems more natural. Highlight
 931                         // closure creation point as a secondary span.
 932                         match db.span.primary_span() {
 933                             Some(primary) => {
 934                                 db.span = MultiSpan::from_span(s);
 935                                 db.span_label(primary, "capture occurs here");
 936                                 db.span_label(s, format!("{} does not live long enough",
 937                                                          value_kind));
 938                                 true
 939                             }
 940                             None => false
 941                         }
 942                     }
 943                     _ => {
 944                         db.span_label(error_span, format!("{} does not live long enough",
 945                                                           value_kind));
 946                         false
 947                     }
 948                 };
 949
 950                 let sub_span = self.region_end_span(sub_scope);
 951                 let super_span = self.region_end_span(super_scope);
 952
 953                 match (sub_span, super_span) {
 954                     (Some(s1), Some(s2)) if s1 == s2 => {
 955                         if !is_closure {
 956                             let msg = match opt_loan_path(&err.cmt) {
 957                                 None => value_kind.to_string(),
 958                                 Some(lp) => {
 959                                     format!("`{}`", self.loan_path_to_string(&lp))
 960                                 }
 961                             };
 962                             db.span_label(s1,
 963                                           format!("{} dropped here while still borrowed", msg));
 964                         } else {
 965                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 966                         }
 967                         db.note("values in a scope are dropped in the opposite order \
 968                                 they are created");
 969                     }
 970                     (Some(s1), Some(s2)) if !is_closure => {
 971                         let msg = match opt_loan_path(&err.cmt) {
 972                             None => value_kind.to_string(),
 973                             Some(lp) => {
 974                                 format!("`{}`", self.loan_path_to_string(&lp))
 975                             }
 976                         };
 977                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 978                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 979                     }
 980                     _ => {
 981                         match sub_span {
 982                             Some(s) => {
 983                                 db.span_label(s, format!("{} needs to live until here",
 984                                                           value_kind));
 985                             }
 986                             None => {
 987                                 self.tcx.note_and_explain_region(
 988                                     &self.region_scope_tree,
 989                                     &mut db,
 990                                     "borrowed value must be valid for ",
 991                                     sub_scope,
 992                                     "...");
 993                             }
 994                         }
 995                         match super_span {
 996                             Some(s) => {
 997                                 db.span_label(s, format!("{} only lives until here", value_kind));
 998                             }
 999                             None => {
1000                                 self.tcx.note_and_explain_region(
1001                                     &self.region_scope_tree,
1002                                     &mut db,
1003                                     "...but borrowed value is only valid for ",
1004                                     super_scope,
1005                                     "");
1006                             }
1007                         }
1008                     }
1009                 }
1010
1011                 if let ty::ReScope(scope) = *super_scope {
1012                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1013                     match self.tcx.hir.find(node_id) {
1014                         Some(hir_map::NodeStmt(_)) => {
1015                             if *sub_scope != ty::ReStatic {
1016                                 db.note("consider using a `let` binding to increase its lifetime");
1017                             }
1018
1019                         }
1020                         _ => {}
1021                     }
1022                 }
1023
1024                 db.emit();
1025             }
1026             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1027                 let descr = self.cmt_to_path_or_string(err.cmt);
1028                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1029                 let descr = match opt_loan_path(&err.cmt) {
1030                     Some(lp) => {
1031                         format!("`{}`", self.loan_path_to_string(&lp))
1032                     }
1033                     None => self.cmt_to_string(&err.cmt),
1034                 };
1035                 self.tcx.note_and_explain_region(
1036                     &self.region_scope_tree,
1037                     &mut db,
1038                     &format!("{} would have to be valid for ",
1039                             descr),
1040                     loan_scope,
1041                     "...");
1042                 self.tcx.note_and_explain_region(
1043                     &self.region_scope_tree,
1044                     &mut db,
1045                     &format!("...but {} is only valid for ", descr),
1046                     ptr_scope,
1047                     "");
1048
1049                 db.emit();
1050             }
1051         }
1052     }
1053
1054     pub fn report_aliasability_violation(&self,
1055                                          span: Span,
1056                                          kind: AliasableViolationKind,
1057                                          cause: mc::AliasableReason,
1058                                          cmt: &mc::cmt_<'tcx>) {
1059         let mut is_closure = false;
1060         let prefix = match kind {
1061             MutabilityViolation => {
1062                 "cannot assign to data"
1063             }
1064             BorrowViolation(euv::ClosureCapture(_)) |
1065             BorrowViolation(euv::OverloadedOperator) |
1066             BorrowViolation(euv::AddrOf) |
1067             BorrowViolation(euv::AutoRef) |
1068             BorrowViolation(euv::AutoUnsafe) |
1069             BorrowViolation(euv::RefBinding) |
1070             BorrowViolation(euv::MatchDiscriminant) => {
1071                 "cannot borrow data mutably"
1072             }
1073
1074             BorrowViolation(euv::ClosureInvocation) => {
1075                 is_closure = true;
1076                 "closure invocation"
1077             }
1078
1079             BorrowViolation(euv::ForLoop) => {
1080                 "`for` loop"
1081             }
1082         };
1083
1084         match cause {
1085             mc::AliasableStaticMut => {
1086                 // This path cannot occur. `static mut X` is not checked
1087                 // for aliasability violations.
1088                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1089             }
1090             mc::AliasableStatic | mc::AliasableBorrowed => {}
1091         };
1092         let blame = cmt.immutability_blame();
1093         let mut err = match blame {
1094             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1095                 // FIXME: the distinction between these 2 messages looks wrong.
1096                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1097                     // The aliasability violation with closure captures can
1098                     // happen for nested closures, so we know the enclosing
1099                     // closure incorrectly accepts an `Fn` while it needs to
1100                     // be `FnMut`.
1101                     "consider changing this to accept closures that implement `FnMut`"
1102
1103                 } else {
1104                     "consider changing this closure to take self by mutable reference"
1105                 };
1106                 let node_id = self.tcx.hir.local_def_id_to_node_id(id);
1107                 let help_span = self.tcx.hir.span(node_id);
1108                 self.cannot_act_on_capture_in_sharable_fn(span,
1109                                                           prefix,
1110                                                           (help_span, help_msg),
1111                                                           Origin::Ast)
1112             }
1113             _ =>  {
1114                 self.cannot_assign_into_immutable_reference(span, prefix,
1115                                                             Origin::Ast)
1116             }
1117         };
1118         self.note_immutability_blame(
1119             &mut err,
1120             blame,
1121             self.tcx.hir.hir_to_node_id(cmt.hir_id)
1122         );
1123
1124         if is_closure {
1125             err.help("closures behind references must be called via `&mut`");
1126         }
1127         err.emit();
1128     }
1129
1130     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1131     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1132         // Check whether the argument is an immutable reference
1133         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1134         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1135             mutbl: hir::Mutability::MutImmutable,
1136             ref ty
1137         }) = pty.node {
1138             // Account for existing lifetimes when generating the message
1139             let pointee_snippet = match self.tcx.sess.codemap().span_to_snippet(ty.span) {
1140                 Ok(snippet) => snippet,
1141                 _ => return None
1142             };
1143
1144             let lifetime_snippet = if !lifetime.is_elided() {
1145                 format!("{} ", match self.tcx.sess.codemap().span_to_snippet(lifetime.span) {
1146                     Ok(lifetime_snippet) => lifetime_snippet,
1147                     _ => return None
1148                 })
1149             } else {
1150                 String::new()
1151             };
1152             Some(format!("use `&{}mut {}` here to make mutable",
1153                          lifetime_snippet,
1154                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1155         } else {
1156             None
1157         }
1158     }
1159
1160     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1161         let pat = match self.tcx.hir.get(node_id) {
1162             hir_map::Node::NodeBinding(pat) => pat,
1163             node => bug!("bad node for local: {:?}", node)
1164         };
1165
1166         match pat.node {
1167             hir::PatKind::Binding(..) => {
1168                 *self.tables
1169                      .pat_binding_modes()
1170                      .get(pat.hir_id)
1171                      .expect("missing binding mode")
1172             }
1173             _ => bug!("local is not a binding: {:?}", pat)
1174         }
1175     }
1176
1177     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1178         let parent = self.tcx.hir.get_parent_node(node_id);
1179         let parent_node = self.tcx.hir.get(parent);
1180
1181         // The parent node is like a fn
1182         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1183             // `nid`'s parent's `Body`
1184             let fn_body = self.tcx.hir.body(fn_like.body());
1185             // Get the position of `node_id` in the arguments list
1186             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1187             if let Some(i) = arg_pos {
1188                 // The argument's `Ty`
1189                 (Some(&fn_like.decl().inputs[i]),
1190                  i == 0 && fn_like.decl().has_implicit_self)
1191             } else {
1192                 (None, false)
1193             }
1194         } else {
1195             (None, false)
1196         }
1197     }
1198
1199     fn note_immutability_blame(&self,
1200                                db: &mut DiagnosticBuilder,
1201                                blame: Option<ImmutabilityBlame>,
1202                                error_node_id: ast::NodeId) {
1203         match blame {
1204             None => {}
1205             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1206             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1207                 self.note_immutable_local(db, error_node_id, node_id)
1208             }
1209             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1210                 match self.local_binding_mode(node_id) {
1211                     ty::BindByReference(..) => {
1212                         let let_span = self.tcx.hir.span(node_id);
1213                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1214                         if let Some((let_span, replace_str)) = suggestion {
1215                             db.span_suggestion(
1216                                 let_span,
1217                                 "use a mutable reference instead",
1218                                 replace_str,
1219                             );
1220                         }
1221                     }
1222                     ty::BindByValue(..) => {
1223                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1224                             if let Some(msg) =
1225                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1226                                 db.span_label(local_ty.span, msg);
1227                             }
1228                         }
1229                     }
1230                 }
1231             }
1232             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1233                 let node_id = match self.tcx.hir.as_local_node_id(field.did) {
1234                     Some(node_id) => node_id,
1235                     None => return
1236                 };
1237
1238                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(node_id) {
1239                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1240                         db.span_label(field.ty.span, msg);
1241                     }
1242                 }
1243             }
1244         }
1245     }
1246
1247      // Suggest a fix when trying to mutably borrow an immutable local
1248      // binding: either to make the binding mutable (if its type is
1249      // not a mutable reference) or to avoid borrowing altogether
1250     fn note_immutable_local(&self,
1251                             db: &mut DiagnosticBuilder,
1252                             borrowed_node_id: ast::NodeId,
1253                             binding_node_id: ast::NodeId) {
1254         let let_span = self.tcx.hir.span(binding_node_id);
1255         if let ty::BindByValue(..) = self.local_binding_mode(binding_node_id) {
1256             if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(let_span) {
1257                 let (ty, is_implicit_self) = self.local_ty(binding_node_id);
1258                 if is_implicit_self && snippet != "self" {
1259                     // avoid suggesting `mut &self`.
1260                     return
1261                 }
1262                 if let Some(&hir::TyKind::Rptr(
1263                     _,
1264                     hir::MutTy {
1265                         mutbl: hir::MutMutable,
1266                         ..
1267                     },
1268                 )) = ty.map(|t| &t.node)
1269                 {
1270                     let borrow_expr_id = self.tcx.hir.get_parent_node(borrowed_node_id);
1271                     db.span_suggestion(
1272                         self.tcx.hir.span(borrow_expr_id),
1273                         "consider removing the `&mut`, as it is an \
1274                         immutable binding to a mutable reference",
1275                         snippet
1276                     );
1277                 } else {
1278                     db.span_label(
1279                         let_span,
1280                         format!("consider changing this to `mut {}`", snippet),
1281                     );
1282                 }
1283             }
1284         }
1285     }
1286
1287     fn report_out_of_scope_escaping_closure_capture(&self,
1288                                                     err: &BckError<'a, 'tcx>,
1289                                                     capture_span: Span)
1290     {
1291         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1292
1293         let suggestion =
1294             match self.tcx.sess.codemap().span_to_snippet(err.span) {
1295                 Ok(string) => format!("move {}", string),
1296                 Err(_) => format!("move |<args>| <body>")
1297             };
1298
1299         self.cannot_capture_in_long_lived_closure(err.span,
1300                                                   &cmt_path_or_string,
1301                                                   capture_span,
1302                                                   Origin::Ast)
1303             .span_suggestion(err.span,
1304                              &format!("to force the closure to take ownership of {} \
1305                                        (and any other referenced variables), \
1306                                        use the `move` keyword",
1307                                        cmt_path_or_string),
1308                              suggestion)
1309             .emit();
1310     }
1311
1312     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1313         match *region {
1314             ty::ReScope(scope) => {
1315                 Some(self.tcx.sess.codemap().end_point(
1316                         scope.span(self.tcx, &self.region_scope_tree)))
1317             }
1318             _ => None
1319         }
1320     }
1321
1322     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'a, 'tcx>,
1323                                     error_span: &Span) {
1324         match err.cmt.note {
1325             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1326                 // If this is an `Fn` closure, it simply can't mutate upvars.
1327                 // If it's an `FnMut` closure, the original variable was declared immutable.
1328                 // We need to determine which is the case here.
1329                 let kind = match err.cmt.upvar_cat().unwrap() {
1330                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1331                     _ => bug!()
1332                 };
1333                 if *kind == ty::ClosureKind::Fn {
1334                     let closure_node_id =
1335                         self.tcx.hir.local_def_id_to_node_id(upvar_id.closure_expr_id);
1336                     db.span_help(self.tcx.hir.span(closure_node_id),
1337                                  "consider changing this closure to take \
1338                                   self by mutable reference");
1339                 }
1340             }
1341             _ => {
1342                 if let Categorization::Deref(..) = err.cmt.cat {
1343                     db.span_label(*error_span, "cannot borrow as mutable");
1344                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1345                     let span = self.tcx.hir.span(local_id);
1346                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1347                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1348                             db.span_label(*error_span, "cannot reborrow mutably");
1349                             db.span_label(*error_span, "try removing `&mut` here");
1350                         } else {
1351                             db.span_label(*error_span, "cannot borrow mutably");
1352                         }
1353                     } else {
1354                         db.span_label(*error_span, "cannot borrow mutably");
1355                     }
1356                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1357                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1358                         db.span_label(*error_span,
1359                                       "cannot mutably borrow field of immutable binding");
1360                     }
1361                 }
1362             }
1363         }
1364     }
1365     pub fn append_loan_path_to_string(&self,
1366                                       loan_path: &LoanPath<'tcx>,
1367                                       out: &mut String) {
1368         match loan_path.kind {
1369             LpUpvar(ty::UpvarId { var_id: id, closure_expr_id: _ }) => {
1370                 out.push_str(&self.tcx.hir.name(self.tcx.hir.hir_to_node_id(id)).as_str());
1371             }
1372             LpVar(id) => {
1373                 out.push_str(&self.tcx.hir.name(id).as_str());
1374             }
1375
1376             LpDowncast(ref lp_base, variant_def_id) => {
1377                 out.push('(');
1378                 self.append_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             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1385                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1386                 out.push('.');
1387                 out.push_str(&info.as_str());
1388             }
1389
1390             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1391                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1392                 out.push_str("[..]");
1393             }
1394
1395             LpExtend(ref lp_base, _, LpDeref(_)) => {
1396                 out.push('*');
1397                 self.append_loan_path_to_string(&lp_base, out);
1398             }
1399         }
1400     }
1401
1402     pub fn append_autoderefd_loan_path_to_string(&self,
1403                                                  loan_path: &LoanPath<'tcx>,
1404                                                  out: &mut String) {
1405         match loan_path.kind {
1406             LpExtend(ref lp_base, _, LpDeref(_)) => {
1407                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1408                 // rules would normally allow users to omit the `*x`.
1409                 // So just serialize such paths to `x.f` or x[3]` respectively.
1410                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1411             }
1412
1413             LpDowncast(ref lp_base, variant_def_id) => {
1414                 out.push('(');
1415                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1416                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1417                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1418                 out.push(')');
1419             }
1420
1421             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1422                 self.append_loan_path_to_string(loan_path, out)
1423             }
1424         }
1425     }
1426
1427     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1428         let mut result = String::new();
1429         self.append_loan_path_to_string(loan_path, &mut result);
1430         result
1431     }
1432
1433     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1434         cmt.descriptive_string(self.tcx)
1435     }
1436
1437     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1438         match opt_loan_path(cmt) {
1439             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1440             None => self.cmt_to_string(cmt),
1441         }
1442     }
1443 }
1444
1445 impl BitwiseOperator for LoanDataFlowOperator {
1446     #[inline]
1447     fn join(&self, succ: usize, pred: usize) -> usize {
1448         succ | pred // loans from both preds are in scope
1449     }
1450 }
1451
1452 impl DataFlowOperator for LoanDataFlowOperator {
1453     #[inline]
1454     fn initial_value(&self) -> bool {
1455         false // no loans in scope by default
1456     }
1457 }
1458
1459 impl<'tcx> fmt::Debug for InteriorKind {
1460     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1461         match *self {
1462             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1463             InteriorElement => write!(f, "[]"),
1464         }
1465     }
1466 }
1467
1468 impl<'tcx> fmt::Debug for Loan<'tcx> {
1469     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1470         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1471                self.index,
1472                self.loan_path,
1473                self.kind,
1474                self.gen_scope,
1475                self.kill_scope,
1476                self.restricted_paths)
1477     }
1478 }
1479
1480 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1481     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1482         match self.kind {
1483             LpVar(id) => {
1484                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1485             }
1486
1487             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1488                 let s = ty::tls::with(|tcx| {
1489                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1490                     tcx.hir.node_to_string(var_node_id)
1491                 });
1492                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1493             }
1494
1495             LpDowncast(ref lp, variant_def_id) => {
1496                 let variant_str = if variant_def_id.is_local() {
1497                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1498                 } else {
1499                     format!("{:?}", variant_def_id)
1500                 };
1501                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1502             }
1503
1504             LpExtend(ref lp, _, LpDeref(_)) => {
1505                 write!(f, "{:?}.*", lp)
1506             }
1507
1508             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1509                 write!(f, "{:?}.{:?}", lp, interior)
1510             }
1511         }
1512     }
1513 }
1514
1515 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1516     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1517         match self.kind {
1518             LpVar(id) => {
1519                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1520             }
1521
1522             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1523                 let s = ty::tls::with(|tcx| {
1524                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1525                     tcx.hir.node_to_string(var_node_id)
1526                 });
1527                 write!(f, "$({} captured by closure)", s)
1528             }
1529
1530             LpDowncast(ref lp, variant_def_id) => {
1531                 let variant_str = if variant_def_id.is_local() {
1532                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1533                 } else {
1534                     format!("{:?}", variant_def_id)
1535                 };
1536                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1537             }
1538
1539             LpExtend(ref lp, _, LpDeref(_)) => {
1540                 write!(f, "{}.*", lp)
1541             }
1542
1543             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1544                 write!(f, "{}.{:?}", lp, interior)
1545             }
1546         }
1547     }
1548 }