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::map as hir_map;
  24 use rustc::hir::map::blocks::FnLikeNode;
  25 use rustc::cfg;
  26 use rustc::middle::dataflow::DataFlowContext;
  27 use rustc::middle::dataflow::BitwiseOperator;
  28 use rustc::middle::dataflow::DataFlowOperator;
  29 use rustc::middle::dataflow::KillFrom;
  30 use rustc::hir::def_id::{DefId, DefIndex};
  31 use rustc::middle::expr_use_visitor as euv;
  32 use rustc::middle::mem_categorization as mc;
  33 use rustc::middle::mem_categorization::Categorization;
  34 use rustc::middle::mem_categorization::ImmutabilityBlame;
  35 use rustc::middle::region;
  36 use rustc::middle::free_region::RegionRelations;
  37 use rustc::ty::{self, Ty, TyCtxt};
  38 use rustc::ty::maps::Providers;
  39 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  40
  41 use std::fmt;
  42 use std::rc::Rc;
  43 use std::hash::{Hash, Hasher};
  44 use syntax::ast;
  45 use syntax_pos::{MultiSpan, Span};
  46 use errors::DiagnosticBuilder;
  47
  48 use rustc::hir;
  49 use rustc::hir::intravisit::{self, Visitor};
  50
  51 pub mod check_loans;
  52
  53 pub mod gather_loans;
  54
  55 pub mod move_data;
  56
  57 #[derive(Clone, Copy)]
  58 pub struct LoanDataFlowOperator;
  59
  60 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  61
  62 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  63     for body_owner_def_id in tcx.body_owners() {
  64         tcx.borrowck(body_owner_def_id);
  65     }
  66 }
  67
  68 pub fn provide(providers: &mut Providers) {
  69     *providers = Providers {
  70         borrowck,
  71         ..*providers
  72     };
  73 }
  74
  75 /// Collection of conclusions determined via borrow checker analyses.
  76 pub struct AnalysisData<'a, 'tcx: 'a> {
  77     pub all_loans: Vec<Loan<'tcx>>,
  78     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  79     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  80 }
  81
  82 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId) {
  83     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  84
  85     let owner_id = tcx.hir.as_local_node_id(owner_def_id).unwrap();
  86
  87     match tcx.hir.get(owner_id) {
  88         hir_map::NodeStructCtor(_) |
  89         hir_map::NodeVariant(_) => {
  90             // We get invoked with anything that has MIR, but some of
  91             // those things (notably the synthesized constructors from
  92             // tuple structs/variants) do not have an associated body
  93             // and do not need borrowchecking.
  94             return;
  95         }
  96         _ => { }
  97     }
  98
  99     let body_id = tcx.hir.body_owned_by(owner_id);
 100     let tables = tcx.typeck_tables_of(owner_def_id);
 101     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 102     let body = tcx.hir.body(body_id);
 103     let bccx = &mut BorrowckCtxt { tcx, tables, region_scope_tree, owner_def_id, body };
 104
 105     // Eventually, borrowck will always read the MIR, but at the
 106     // moment we do not. So, for now, we always force MIR to be
 107     // constructed for a given fn, since this may result in errors
 108     // being reported and we want that to happen.
 109     //
 110     // Note that `mir_validated` is a "stealable" result; the
 111     // thief, `optimized_mir()`, forces borrowck, so we know that
 112     // is not yet stolen.
 113     tcx.mir_validated(owner_def_id).borrow();
 114
 115     // option dance because you can't capture an uninitialized variable
 116     // by mut-ref.
 117     let mut cfg = None;
 118     if let Some(AnalysisData { all_loans,
 119                                loans: loan_dfcx,
 120                                move_data: flowed_moves }) =
 121         build_borrowck_dataflow_data(bccx, false, body_id,
 122                                      |bccx| {
 123                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 124                                          cfg.as_mut().unwrap()
 125                                      })
 126     {
 127         check_loans::check_loans(bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 128     }
 129 }
 130
 131 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 132                                                  force_analysis: bool,
 133                                                  body_id: hir::BodyId,
 134                                                  get_cfg: F)
 135                                                  -> Option<AnalysisData<'a, 'tcx>>
 136     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 137 {
 138     // Check the body of fn items.
 139     let tcx = this.tcx;
 140     let id_range = {
 141         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir);
 142         visitor.visit_body(this.body);
 143         visitor.result()
 144     };
 145     let (all_loans, move_data) =
 146         gather_loans::gather_loans_in_fn(this, body_id);
 147
 148     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 149         // large arrays of data inserted as constants can take a lot of
 150         // time and memory to borrow-check - see issue #36799. However,
 151         // they don't have lvalues, so no borrow-check is actually needed.
 152         // Recognize that case and skip borrow-checking.
 153         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 154         return None;
 155     } else {
 156         debug!("propagating loans in {:?}", body_id);
 157     }
 158
 159     let cfg = get_cfg(this);
 160     let mut loan_dfcx =
 161         DataFlowContext::new(this.tcx,
 162                              "borrowck",
 163                              Some(this.body),
 164                              cfg,
 165                              LoanDataFlowOperator,
 166                              id_range,
 167                              all_loans.len());
 168     for (loan_idx, loan) in all_loans.iter().enumerate() {
 169         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 170         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 171                            loan.kill_scope.item_local_id(),
 172                            loan_idx);
 173     }
 174     loan_dfcx.add_kills_from_flow_exits(cfg);
 175     loan_dfcx.propagate(cfg, this.body);
 176
 177     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 178                                                       this,
 179                                                       cfg,
 180                                                       id_range,
 181                                                       this.body);
 182
 183     Some(AnalysisData { all_loans,
 184                         loans: loan_dfcx,
 185                         move_data:flowed_moves })
 186 }
 187
 188 /// Accessor for introspective clients inspecting `AnalysisData` and
 189 /// the `BorrowckCtxt` itself , e.g. the flowgraph visualizer.
 190 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 191     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 192     body_id: hir::BodyId,
 193     cfg: &cfg::CFG)
 194     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 195 {
 196     let owner_id = tcx.hir.body_owner(body_id);
 197     let owner_def_id = tcx.hir.local_def_id(owner_id);
 198     let tables = tcx.typeck_tables_of(owner_def_id);
 199     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 200     let body = tcx.hir.body(body_id);
 201     let mut bccx = BorrowckCtxt { tcx, tables, region_scope_tree, owner_def_id, body };
 202
 203     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 204     (bccx, dataflow_data.unwrap())
 205 }
 206
 207 // ----------------------------------------------------------------------
 208 // Type definitions
 209
 210 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 211     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 212
 213     // tables for the current thing we are checking; set to
 214     // Some in `borrowck_fn` and cleared later
 215     tables: &'a ty::TypeckTables<'tcx>,
 216
 217     region_scope_tree: Rc<region::ScopeTree>,
 218
 219     owner_def_id: DefId,
 220
 221     body: &'tcx hir::Body,
 222 }
 223
 224 impl<'b, 'tcx: 'b> BorrowckErrors for BorrowckCtxt<'b, 'tcx> {
 225     fn struct_span_err_with_code<'a, S: Into<MultiSpan>>(&'a self,
 226                                                          sp: S,
 227                                                          msg: &str,
 228                                                          code: &str)
 229                                                          -> DiagnosticBuilder<'a>
 230     {
 231         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 232     }
 233
 234     fn struct_span_err<'a, S: Into<MultiSpan>>(&'a self,
 235                                                sp: S,
 236                                                msg: &str)
 237                                                -> DiagnosticBuilder<'a>
 238     {
 239         self.tcx.sess.struct_span_err(sp, msg)
 240     }
 241 }
 242
 243 ///////////////////////////////////////////////////////////////////////////
 244 // Loans and loan paths
 245
 246 /// Record of a loan that was issued.
 247 pub struct Loan<'tcx> {
 248     index: usize,
 249     loan_path: Rc<LoanPath<'tcx>>,
 250     kind: ty::BorrowKind,
 251     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 252
 253     /// gen_scope indicates where loan is introduced. Typically the
 254     /// loan is introduced at the point of the borrow, but in some
 255     /// cases, notably method arguments, the loan may be introduced
 256     /// only later, once it comes into scope.  See also
 257     /// `GatherLoanCtxt::compute_gen_scope`.
 258     gen_scope: region::Scope,
 259
 260     /// kill_scope indicates when the loan goes out of scope.  This is
 261     /// either when the lifetime expires or when the local variable
 262     /// which roots the loan-path goes out of scope, whichever happens
 263     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 264     kill_scope: region::Scope,
 265     span: Span,
 266     cause: euv::LoanCause,
 267 }
 268
 269 impl<'tcx> Loan<'tcx> {
 270     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 271         self.loan_path.clone()
 272     }
 273 }
 274
 275 #[derive(Eq)]
 276 pub struct LoanPath<'tcx> {
 277     kind: LoanPathKind<'tcx>,
 278     ty: Ty<'tcx>,
 279 }
 280
 281 impl<'tcx> PartialEq for LoanPath<'tcx> {
 282     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 283         self.kind == that.kind
 284     }
 285 }
 286
 287 impl<'tcx> Hash for LoanPath<'tcx> {
 288     fn hash<H: Hasher>(&self, state: &mut H) {
 289         self.kind.hash(state);
 290     }
 291 }
 292
 293 #[derive(PartialEq, Eq, Hash, Debug)]
 294 pub enum LoanPathKind<'tcx> {
 295     LpVar(ast::NodeId),                         // `x` in README.md
 296     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 297     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 298     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 299 }
 300
 301 impl<'tcx> LoanPath<'tcx> {
 302     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 303         LoanPath { kind: kind, ty: ty }
 304     }
 305
 306     fn to_type(&self) -> Ty<'tcx> { self.ty }
 307 }
 308
 309 // FIXME (pnkfelix): See discussion here
 310 // https://github.com/pnkfelix/rust/commit/
 311 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 312 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 313
 314 // A local, "cleaned" version of `mc::InteriorKind` that drops
 315 // information that is not relevant to loan-path analysis. (In
 316 // particular, the distinction between how precisely an array-element
 317 // is tracked is irrelevant here.)
 318 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 319 pub enum InteriorKind {
 320     InteriorField(mc::FieldName),
 321     InteriorElement,
 322 }
 323
 324 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 325 impl ToInteriorKind for mc::InteriorKind {
 326     fn cleaned(self) -> InteriorKind {
 327         match self {
 328             mc::InteriorField(name) => InteriorField(name),
 329             mc::InteriorElement(_) => InteriorElement,
 330         }
 331     }
 332 }
 333
 334 // This can be:
 335 // - a pointer dereference (`*LV` in README.md)
 336 // - a field reference, with an optional definition of the containing
 337 //   enum variant (`LV.f` in README.md)
 338 // `DefId` is present when the field is part of struct that is in
 339 // a variant of an enum. For instance in:
 340 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 341 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 342 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 343 pub enum LoanPathElem<'tcx> {
 344     LpDeref(mc::PointerKind<'tcx>),
 345     LpInterior(Option<DefId>, InteriorKind),
 346 }
 347
 348 fn closure_to_block(closure_id: DefIndex,
 349                     tcx: TyCtxt) -> ast::NodeId {
 350     let closure_id = tcx.hir.def_index_to_node_id(closure_id);
 351     match tcx.hir.get(closure_id) {
 352         hir_map::NodeExpr(expr) => match expr.node {
 353             hir::ExprClosure(.., body_id, _, _) => {
 354                 body_id.node_id
 355             }
 356             _ => {
 357                 bug!("encountered non-closure id: {}", closure_id)
 358             }
 359         },
 360         _ => bug!("encountered non-expr id: {}", closure_id)
 361     }
 362 }
 363
 364 impl<'a, 'tcx> LoanPath<'tcx> {
 365     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 366         match self.kind {
 367             LpVar(local_id) => {
 368                 let hir_id = bccx.tcx.hir.node_to_hir_id(local_id);
 369                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 370             }
 371             LpUpvar(upvar_id) => {
 372                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 373                 let hir_id = bccx.tcx.hir.node_to_hir_id(block_id);
 374                 region::Scope::Node(hir_id.local_id)
 375             }
 376             LpDowncast(ref base, _) |
 377             LpExtend(ref base, ..) => base.kill_scope(bccx),
 378         }
 379     }
 380
 381     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 382         match (&self.kind, &other.kind) {
 383             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 384              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 385                 if id == id2 && opt_variant_id == opt_variant_id2 {
 386                     base.has_fork(&base2)
 387                 } else {
 388                     true
 389                 },
 390             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 391             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 392             _ => false,
 393         }
 394     }
 395
 396     fn depth(&self) -> usize {
 397         match self.kind {
 398             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 399             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 400             _ => 0,
 401         }
 402     }
 403
 404     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 405         match (&self.kind, &other.kind) {
 406             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 407              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 408                 if id == id2 && opt_variant_id == opt_variant_id2 {
 409                     base.common(&base2).map(|x| {
 410                         let xd = x.depth();
 411                         if base.depth() == xd && base2.depth() == xd {
 412                             LoanPath {
 413                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 414                                 ty: self.ty,
 415                             }
 416                         } else {
 417                             x
 418                         }
 419                     })
 420                 } else {
 421                     base.common(&base2)
 422                 }
 423             }
 424             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 425             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 426             (&LpVar(id), &LpVar(id2)) => {
 427                 if id == id2 {
 428                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 429                 } else {
 430                     None
 431                 }
 432             }
 433             (&LpUpvar(id), &LpUpvar(id2)) => {
 434                 if id == id2 {
 435                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 436                 } else {
 437                     None
 438                 }
 439             }
 440             _ => None,
 441         }
 442     }
 443 }
 444
 445 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 446     //! Computes the `LoanPath` (if any) for a `cmt`.
 447     //! Note that this logic is somewhat duplicated in
 448     //! the method `compute()` found in `gather_loans::restrictions`,
 449     //! which allows it to share common loan path pieces as it
 450     //! traverses the CMT.
 451
 452     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 453
 454     match cmt.cat {
 455         Categorization::Rvalue(..) |
 456         Categorization::StaticItem => {
 457             None
 458         }
 459
 460         Categorization::Local(id) => {
 461             Some(new_lp(LpVar(id)))
 462         }
 463
 464         Categorization::Upvar(mc::Upvar { id, .. }) => {
 465             Some(new_lp(LpUpvar(id)))
 466         }
 467
 468         Categorization::Deref(ref cmt_base, pk) => {
 469             opt_loan_path(cmt_base).map(|lp| {
 470                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 471             })
 472         }
 473
 474         Categorization::Interior(ref cmt_base, ik) => {
 475             opt_loan_path(cmt_base).map(|lp| {
 476                 let opt_variant_id = match cmt_base.cat {
 477                     Categorization::Downcast(_, did) =>  Some(did),
 478                     _ => None
 479                 };
 480                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 481             })
 482         }
 483
 484         Categorization::Downcast(ref cmt_base, variant_def_id) =>
 485             opt_loan_path(cmt_base)
 486             .map(|lp| {
 487                 new_lp(LpDowncast(lp, variant_def_id))
 488             }),
 489
 490     }
 491 }
 492
 493 ///////////////////////////////////////////////////////////////////////////
 494 // Errors
 495
 496 // Errors that can occur
 497 #[derive(Debug, PartialEq)]
 498 pub enum bckerr_code<'tcx> {
 499     err_mutbl,
 500     /// superscope, subscope, loan cause
 501     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 502     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 503 }
 504
 505 // Combination of an error code and the categorization of the expression
 506 // that caused it
 507 #[derive(Debug, PartialEq)]
 508 pub struct BckError<'tcx> {
 509     span: Span,
 510     cause: AliasableViolationKind,
 511     cmt: mc::cmt<'tcx>,
 512     code: bckerr_code<'tcx>
 513 }
 514
 515 #[derive(Copy, Clone, Debug, PartialEq)]
 516 pub enum AliasableViolationKind {
 517     MutabilityViolation,
 518     BorrowViolation(euv::LoanCause)
 519 }
 520
 521 #[derive(Copy, Clone, Debug)]
 522 pub enum MovedValueUseKind {
 523     MovedInUse,
 524     MovedInCapture,
 525 }
 526
 527 ///////////////////////////////////////////////////////////////////////////
 528 // Misc
 529
 530 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 531     pub fn is_subregion_of(&self,
 532                            r_sub: ty::Region<'tcx>,
 533                            r_sup: ty::Region<'tcx>)
 534                            -> bool
 535     {
 536         let region_rels = RegionRelations::new(self.tcx,
 537                                                self.owner_def_id,
 538                                                &self.region_scope_tree,
 539                                                &self.tables.free_region_map);
 540         region_rels.is_subregion_of(r_sub, r_sup)
 541     }
 542
 543     pub fn report(&self, err: BckError<'tcx>) {
 544         // Catch and handle some particular cases.
 545         match (&err.code, &err.cause) {
 546             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 547              &BorrowViolation(euv::ClosureCapture(span))) |
 548             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 549              &BorrowViolation(euv::ClosureCapture(span))) |
 550             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 551              &BorrowViolation(euv::ClosureCapture(span))) => {
 552                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 553             }
 554             _ => { }
 555         }
 556
 557         self.report_bckerr(&err);
 558     }
 559
 560     pub fn report_use_of_moved_value(&self,
 561                                      use_span: Span,
 562                                      use_kind: MovedValueUseKind,
 563                                      lp: &LoanPath<'tcx>,
 564                                      the_move: &move_data::Move,
 565                                      moved_lp: &LoanPath<'tcx>,
 566                                      _param_env: ty::ParamEnv<'tcx>) {
 567         let (verb, verb_participle) = match use_kind {
 568             MovedInUse => ("use", "used"),
 569             MovedInCapture => ("capture", "captured"),
 570         };
 571
 572         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 573             move_data::Declared => {
 574                 // If this is an uninitialized variable, just emit a simple warning
 575                 // and return.
 576                 self.cannot_act_on_uninitialized_variable(use_span,
 577                                                           verb,
 578                                                           &self.loan_path_to_string(lp),
 579                                                           Origin::Ast)
 580                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 581                                                   self.loan_path_to_string(lp)))
 582                     .emit();
 583                 return;
 584             }
 585             _ => {
 586                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 587                 // normally generate a rather confusing message:
 588                 //
 589                 //     error: use of moved value: `x.b`
 590                 //     note: `x.a` moved here...
 591                 //
 592                 // What we want to do instead is get the 'common ancestor' of the two moves and
 593                 // use that for most of the message instead, giving is something like this:
 594                 //
 595                 //     error: use of moved value: `x`
 596                 //     note: `x` moved here (through moving `x.a`)...
 597
 598                 let common = moved_lp.common(lp);
 599                 let has_common = common.is_some();
 600                 let has_fork = moved_lp.has_fork(lp);
 601                 let (nl, ol, moved_lp_msg) =
 602                     if has_fork && has_common {
 603                         let nl = self.loan_path_to_string(&common.unwrap());
 604                         let ol = nl.clone();
 605                         let moved_lp_msg = format!(" (through moving `{}`)",
 606                                                    self.loan_path_to_string(moved_lp));
 607                         (nl, ol, moved_lp_msg)
 608                     } else {
 609                         (self.loan_path_to_string(lp),
 610                          self.loan_path_to_string(moved_lp),
 611                          String::new())
 612                     };
 613
 614                 let partial = moved_lp.depth() > lp.depth();
 615                 let msg = if !has_fork && partial { "partially " }
 616                           else if has_fork && !has_common { "collaterally "}
 617                           else { "" };
 618                 let mut err = struct_span_err!(
 619                     self.tcx.sess, use_span, E0382,
 620                     "{} of {}moved value: `{}`",
 621                     verb, msg, nl);
 622                 let need_note = match lp.ty.sty {
 623                     ty::TypeVariants::TyClosure(id, _) => {
 624                         let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
 625                         let hir_id = self.tcx.hir.node_to_hir_id(node_id);
 626                         if let Some(&(ty::ClosureKind::FnOnce, Some((span, name)))) =
 627                             self.tables.closure_kinds().get(hir_id)
 628                         {
 629                             err.span_note(span, &format!(
 630                                 "closure cannot be invoked more than once because \
 631                                 it moves the variable `{}` out of its environment",
 632                                 name
 633                             ));
 634                             false
 635                         } else {
 636                             true
 637                         }
 638                     }
 639                     _ => true,
 640                 };
 641                 (ol, moved_lp_msg, err, need_note)
 642             }
 643         };
 644
 645         // Get type of value and span where it was previously
 646         // moved.
 647         let node_id = self.tcx.hir.hir_to_node_id(hir::HirId {
 648             owner: self.body.value.hir_id.owner,
 649             local_id: the_move.id
 650         });
 651         let (move_span, move_note) = match the_move.kind {
 652             move_data::Declared => {
 653                 unreachable!();
 654             }
 655
 656             move_data::MoveExpr |
 657             move_data::MovePat => (self.tcx.hir.span(node_id), ""),
 658
 659             move_data::Captured =>
 660                 (match self.tcx.hir.expect_expr(node_id).node {
 661                     hir::ExprClosure(.., fn_decl_span, _) => fn_decl_span,
 662                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 663                                   the_move.id, r),
 664                 }, " (into closure)"),
 665         };
 666
 667         // Annotate the use and the move in the span. Watch out for
 668         // the case where the use and the move are the same. This
 669         // means the use is in a loop.
 670         err = if use_span == move_span {
 671             err.span_label(
 672                 use_span,
 673                 format!("value moved{} here in previous iteration of loop",
 674                          move_note));
 675             err
 676         } else {
 677             err.span_label(use_span, format!("value {} here after move", verb_participle))
 678                .span_label(move_span, format!("value moved{} here", move_note));
 679             err
 680         };
 681
 682         if need_note {
 683             err.note(&format!("move occurs because `{}` has type `{}`, \
 684                                which does not implement the `Copy` trait",
 685                               self.loan_path_to_string(moved_lp),
 686                               moved_lp.ty));
 687         }
 688
 689         // Note: we used to suggest adding a `ref binding` or calling
 690         // `clone` but those suggestions have been removed because
 691         // they are often not what you actually want to do, and were
 692         // not considered particularly helpful.
 693
 694         err.emit();
 695     }
 696
 697     pub fn report_partial_reinitialization_of_uninitialized_structure(
 698             &self,
 699             span: Span,
 700             lp: &LoanPath<'tcx>) {
 701         span_err!(
 702             self.tcx.sess, span, E0383,
 703             "partial reinitialization of uninitialized structure `{}`",
 704             self.loan_path_to_string(lp));
 705     }
 706
 707     pub fn report_reassigned_immutable_variable(&self,
 708                                                 span: Span,
 709                                                 lp: &LoanPath<'tcx>,
 710                                                 assign:
 711                                                 &move_data::Assignment) {
 712         let mut err = self.cannot_reassign_immutable(span,
 713                                                      &self.loan_path_to_string(lp),
 714                                                      Origin::Ast);
 715         err.span_label(span, "re-assignment of immutable variable");
 716         if span != assign.span {
 717             err.span_label(assign.span, format!("first assignment to `{}`",
 718                                               self.loan_path_to_string(lp)));
 719         }
 720         err.emit();
 721     }
 722
 723     pub fn struct_span_err_with_code<S: Into<MultiSpan>>(&self,
 724                                                          s: S,
 725                                                          msg: &str,
 726                                                          code: &str)
 727                                                          -> DiagnosticBuilder<'a> {
 728         self.tcx.sess.struct_span_err_with_code(s, msg, code)
 729     }
 730
 731     pub fn span_err_with_code<S: Into<MultiSpan>>(&self, s: S, msg: &str, code: &str) {
 732         self.tcx.sess.span_err_with_code(s, msg, code);
 733     }
 734
 735     fn report_bckerr(&self, err: &BckError<'tcx>) {
 736         let error_span = err.span.clone();
 737
 738         match err.code {
 739             err_mutbl => {
 740                 let descr = match err.cmt.note {
 741                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 742                         self.cmt_to_string(&err.cmt)
 743                     }
 744                     _ => match opt_loan_path(&err.cmt) {
 745                         None => {
 746                             format!("{} {}",
 747                                     err.cmt.mutbl.to_user_str(),
 748                                     self.cmt_to_string(&err.cmt))
 749
 750                         }
 751                         Some(lp) => {
 752                             format!("{} {} `{}`",
 753                                     err.cmt.mutbl.to_user_str(),
 754                                     self.cmt_to_string(&err.cmt),
 755                                     self.loan_path_to_string(&lp))
 756                         }
 757                     }
 758                 };
 759
 760                 let mut db = match err.cause {
 761                     MutabilityViolation => {
 762                         struct_span_err!(self.tcx.sess,
 763                                          error_span,
 764                                          E0594,
 765                                          "cannot assign to {}",
 766                                          descr)
 767                     }
 768                     BorrowViolation(euv::ClosureCapture(_)) => {
 769                         struct_span_err!(self.tcx.sess, error_span, E0595,
 770                                          "closure cannot assign to {}", descr)
 771                     }
 772                     BorrowViolation(euv::OverloadedOperator) |
 773                     BorrowViolation(euv::AddrOf) |
 774                     BorrowViolation(euv::RefBinding) |
 775                     BorrowViolation(euv::AutoRef) |
 776                     BorrowViolation(euv::AutoUnsafe) |
 777                     BorrowViolation(euv::ForLoop) |
 778                     BorrowViolation(euv::MatchDiscriminant) => {
 779                         struct_span_err!(self.tcx.sess, error_span, E0596,
 780                                          "cannot borrow {} as mutable", descr)
 781                     }
 782                     BorrowViolation(euv::ClosureInvocation) => {
 783                         span_bug!(err.span,
 784                             "err_mutbl with a closure invocation");
 785                     }
 786                 };
 787
 788                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 789                 self.note_immutability_blame(&mut db, err.cmt.immutability_blame());
 790                 db.emit();
 791             }
 792             err_out_of_scope(super_scope, sub_scope, cause) => {
 793                 let msg = match opt_loan_path(&err.cmt) {
 794                     None => "borrowed value".to_string(),
 795                     Some(lp) => {
 796                         format!("`{}`", self.loan_path_to_string(&lp))
 797                     }
 798                 };
 799
 800                 // When you have a borrow that lives across a yield,
 801                 // that reference winds up captured in the generator
 802                 // type. Regionck then constraints it to live as long
 803                 // as the generator itself. If that borrow is borrowing
 804                 // data owned by the generator, this winds up resulting in
 805                 // an `err_out_of_scope` error:
 806                 //
 807                 // ```
 808                 // {
 809                 //     let g = || {
 810                 //         let a = &3; // this borrow is forced to ... -+
 811                 //         yield ();          //                        |
 812                 //         println!("{}", a); //                        |
 813                 //     };                     //                        |
 814                 // } <----------------------... live until here --------+
 815                 // ```
 816                 //
 817                 // To detect this case, we look for cases where the
 818                 // `super_scope` (lifetime of the value) is within the
 819                 // body, but the `sub_scope` is not.
 820                 debug!("err_out_of_scope: self.body.is_generator = {:?}",
 821                        self.body.is_generator);
 822                 let maybe_borrow_across_yield = if self.body.is_generator {
 823                     let body_scope = region::Scope::Node(self.body.value.hir_id.local_id);
 824                     debug!("err_out_of_scope: body_scope = {:?}", body_scope);
 825                     debug!("err_out_of_scope: super_scope = {:?}", super_scope);
 826                     debug!("err_out_of_scope: sub_scope = {:?}", sub_scope);
 827                     match (super_scope, sub_scope) {
 828                         (&ty::RegionKind::ReScope(value_scope),
 829                          &ty::RegionKind::ReScope(loan_scope)) => {
 830                             if {
 831                                 // value_scope <= body_scope &&
 832                                 self.region_scope_tree.is_subscope_of(value_scope, body_scope) &&
 833                                     // body_scope <= loan_scope
 834                                     self.region_scope_tree.is_subscope_of(body_scope, loan_scope)
 835                             } {
 836                                 // We now know that this is a case
 837                                 // that fits the bill described above:
 838                                 // a borrow of something whose scope
 839                                 // is within the generator, but the
 840                                 // borrow is for a scope outside the
 841                                 // generator.
 842                                 //
 843                                 // Now look within the scope of the of
 844                                 // the value being borrowed (in the
 845                                 // example above, that would be the
 846                                 // block remainder that starts with
 847                                 // `let a`) for a yield. We can cite
 848                                 // that for the user.
 849                                 self.region_scope_tree.yield_in_scope(value_scope)
 850                             } else {
 851                                 None
 852                             }
 853                         }
 854                         _ => None,
 855                     }
 856                 } else {
 857                     None
 858                 };
 859
 860                 if let Some((yield_span, _)) = maybe_borrow_across_yield {
 861                     debug!("err_out_of_scope: opt_yield_span = {:?}", yield_span);
 862                     struct_span_err!(self.tcx.sess,
 863                                      error_span,
 864                                      E0626,
 865                                      "borrow may still be in use when generator yields")
 866                         .span_label(yield_span, "possible yield occurs here")
 867                         .emit();
 868                     return;
 869                 }
 870
 871                 let mut db = struct_span_err!(self.tcx.sess,
 872                                               error_span,
 873                                               E0597,
 874                                               "{} does not live long enough",
 875                                               msg);
 876
 877                 let (value_kind, value_msg) = match err.cmt.cat {
 878                     mc::Categorization::Rvalue(..) =>
 879                         ("temporary value", "temporary value created here"),
 880                     _ =>
 881                         ("borrowed value", "borrow occurs here")
 882                 };
 883
 884                 let is_closure = match cause {
 885                     euv::ClosureCapture(s) => {
 886                         // The primary span starts out as the closure creation point.
 887                         // Change the primary span here to highlight the use of the variable
 888                         // in the closure, because it seems more natural. Highlight
 889                         // closure creation point as a secondary span.
 890                         match db.span.primary_span() {
 891                             Some(primary) => {
 892                                 db.span = MultiSpan::from_span(s);
 893                                 db.span_label(primary, "capture occurs here");
 894                                 db.span_label(s, "does not live long enough");
 895                                 true
 896                             }
 897                             None => false
 898                         }
 899                     }
 900                     _ => {
 901                         db.span_label(error_span, "does not live long enough");
 902                         false
 903                     }
 904                 };
 905
 906                 let sub_span = self.region_end_span(sub_scope);
 907                 let super_span = self.region_end_span(super_scope);
 908
 909                 match (sub_span, super_span) {
 910                     (Some(s1), Some(s2)) if s1 == s2 => {
 911                         if !is_closure {
 912                             db.span = MultiSpan::from_span(s1);
 913                             db.span_label(error_span, value_msg);
 914                             let msg = match opt_loan_path(&err.cmt) {
 915                                 None => value_kind.to_string(),
 916                                 Some(lp) => {
 917                                     format!("`{}`", self.loan_path_to_string(&lp))
 918                                 }
 919                             };
 920                             db.span_label(s1,
 921                                           format!("{} dropped here while still borrowed", msg));
 922                         } else {
 923                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 924                         }
 925                         db.note("values in a scope are dropped in the opposite order \
 926                                 they are created");
 927                     }
 928                     (Some(s1), Some(s2)) if !is_closure => {
 929                         db.span = MultiSpan::from_span(s2);
 930                         db.span_label(error_span, value_msg);
 931                         let msg = match opt_loan_path(&err.cmt) {
 932                             None => value_kind.to_string(),
 933                             Some(lp) => {
 934                                 format!("`{}`", self.loan_path_to_string(&lp))
 935                             }
 936                         };
 937                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 938                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 939                     }
 940                     _ => {
 941                         match sub_span {
 942                             Some(s) => {
 943                                 db.span_label(s, format!("{} needs to live until here",
 944                                                           value_kind));
 945                             }
 946                             None => {
 947                                 self.tcx.note_and_explain_region(
 948                                     &self.region_scope_tree,
 949                                     &mut db,
 950                                     "borrowed value must be valid for ",
 951                                     sub_scope,
 952                                     "...");
 953                             }
 954                         }
 955                         match super_span {
 956                             Some(s) => {
 957                                 db.span_label(s, format!("{} only lives until here", value_kind));
 958                             }
 959                             None => {
 960                                 self.tcx.note_and_explain_region(
 961                                     &self.region_scope_tree,
 962                                     &mut db,
 963                                     "...but borrowed value is only valid for ",
 964                                     super_scope,
 965                                     "");
 966                             }
 967                         }
 968                     }
 969                 }
 970
 971                 if let ty::ReScope(scope) = *super_scope {
 972                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
 973                     match self.tcx.hir.find(node_id) {
 974                         Some(hir_map::NodeStmt(_)) => {
 975                             db.note("consider using a `let` binding to increase its lifetime");
 976                         }
 977                         _ => {}
 978                     }
 979                 }
 980
 981                 db.emit();
 982             }
 983             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
 984                 let descr = self.cmt_to_path_or_string(&err.cmt);
 985                 let mut db = struct_span_err!(self.tcx.sess, error_span, E0598,
 986                                               "lifetime of {} is too short to guarantee \
 987                                                its contents can be safely reborrowed",
 988                                               descr);
 989
 990                 let descr = match opt_loan_path(&err.cmt) {
 991                     Some(lp) => {
 992                         format!("`{}`", self.loan_path_to_string(&lp))
 993                     }
 994                     None => self.cmt_to_string(&err.cmt),
 995                 };
 996                 self.tcx.note_and_explain_region(
 997                     &self.region_scope_tree,
 998                     &mut db,
 999                     &format!("{} would have to be valid for ",
1000                             descr),
1001                     loan_scope,
1002                     "...");
1003                 self.tcx.note_and_explain_region(
1004                     &self.region_scope_tree,
1005                     &mut db,
1006                     &format!("...but {} is only valid for ", descr),
1007                     ptr_scope,
1008                     "");
1009
1010                 db.emit();
1011             }
1012         }
1013     }
1014
1015     pub fn report_aliasability_violation(&self,
1016                                          span: Span,
1017                                          kind: AliasableViolationKind,
1018                                          cause: mc::AliasableReason,
1019                                          cmt: mc::cmt<'tcx>) {
1020         let mut is_closure = false;
1021         let prefix = match kind {
1022             MutabilityViolation => {
1023                 "cannot assign to data"
1024             }
1025             BorrowViolation(euv::ClosureCapture(_)) |
1026             BorrowViolation(euv::OverloadedOperator) |
1027             BorrowViolation(euv::AddrOf) |
1028             BorrowViolation(euv::AutoRef) |
1029             BorrowViolation(euv::AutoUnsafe) |
1030             BorrowViolation(euv::RefBinding) |
1031             BorrowViolation(euv::MatchDiscriminant) => {
1032                 "cannot borrow data mutably"
1033             }
1034
1035             BorrowViolation(euv::ClosureInvocation) => {
1036                 is_closure = true;
1037                 "closure invocation"
1038             }
1039
1040             BorrowViolation(euv::ForLoop) => {
1041                 "`for` loop"
1042             }
1043         };
1044
1045         match cause {
1046             mc::AliasableStatic |
1047             mc::AliasableStaticMut => {
1048                 // This path cannot occur. It happens when we have an
1049                 // `&mut` or assignment to a static. But in the case
1050                 // of `static X`, we get a mutability violation first,
1051                 // and never get here. In the case of `static mut X`,
1052                 // that is unsafe and hence the aliasability error is
1053                 // ignored.
1054                 span_bug!(span, "aliasability violation for static `{}`", prefix)
1055             }
1056             mc::AliasableBorrowed => {}
1057         };
1058         let blame = cmt.immutability_blame();
1059         let mut err = match blame {
1060             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1061                 let mut err = struct_span_err!(
1062                     self.tcx.sess, span, E0387,
1063                     "{} in a captured outer variable in an `Fn` closure", prefix);
1064
1065                 // FIXME: the distinction between these 2 messages looks wrong.
1066                 let help = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1067                     // The aliasability violation with closure captures can
1068                     // happen for nested closures, so we know the enclosing
1069                     // closure incorrectly accepts an `Fn` while it needs to
1070                     // be `FnMut`.
1071                     "consider changing this to accept closures that implement `FnMut`"
1072
1073                 } else {
1074                     "consider changing this closure to take self by mutable reference"
1075                 };
1076                 let node_id = self.tcx.hir.def_index_to_node_id(id);
1077                 err.span_help(self.tcx.hir.span(node_id), help);
1078                 err
1079             }
1080             _ =>  {
1081                 let mut err = struct_span_err!(
1082                     self.tcx.sess, span, E0389,
1083                     "{} in a `&` reference", prefix);
1084                 err.span_label(span, "assignment into an immutable reference");
1085                 err
1086             }
1087         };
1088         self.note_immutability_blame(&mut err, blame);
1089
1090         if is_closure {
1091             err.help("closures behind references must be called via `&mut`");
1092         }
1093         err.emit();
1094     }
1095
1096     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1097     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1098         // Check wether the argument is an immutable reference
1099         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1100         if let hir::TyRptr(lifetime, hir::MutTy {
1101             mutbl: hir::Mutability::MutImmutable,
1102             ref ty
1103         }) = pty.node {
1104             // Account for existing lifetimes when generating the message
1105             let pointee_snippet = match self.tcx.sess.codemap().span_to_snippet(ty.span) {
1106                 Ok(snippet) => snippet,
1107                 _ => return None
1108             };
1109
1110             let lifetime_snippet = if !lifetime.is_elided() {
1111                 format!("{} ", match self.tcx.sess.codemap().span_to_snippet(lifetime.span) {
1112                     Ok(lifetime_snippet) => lifetime_snippet,
1113                     _ => return None
1114                 })
1115             } else {
1116                 String::new()
1117             };
1118             Some(format!("use `&{}mut {}` here to make mutable",
1119                          lifetime_snippet,
1120                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1121         } else {
1122             None
1123         }
1124     }
1125
1126     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1127         let pat = match self.tcx.hir.get(node_id) {
1128             hir_map::Node::NodeBinding(pat) => pat,
1129             node => bug!("bad node for local: {:?}", node)
1130         };
1131
1132         match pat.node {
1133             hir::PatKind::Binding(..) => {
1134                 *self.tables
1135                      .pat_binding_modes()
1136                      .get(pat.hir_id)
1137                      .expect("missing binding mode")
1138             }
1139             _ => bug!("local is not a binding: {:?}", pat)
1140         }
1141     }
1142
1143     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1144         let parent = self.tcx.hir.get_parent_node(node_id);
1145         let parent_node = self.tcx.hir.get(parent);
1146
1147         // The parent node is like a fn
1148         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1149             // `nid`'s parent's `Body`
1150             let fn_body = self.tcx.hir.body(fn_like.body());
1151             // Get the position of `node_id` in the arguments list
1152             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1153             if let Some(i) = arg_pos {
1154                 // The argument's `Ty`
1155                 (Some(&fn_like.decl().inputs[i]),
1156                  i == 0 && fn_like.decl().has_implicit_self)
1157             } else {
1158                 (None, false)
1159             }
1160         } else {
1161             (None, false)
1162         }
1163     }
1164
1165     fn note_immutability_blame(&self,
1166                                db: &mut DiagnosticBuilder,
1167                                blame: Option<ImmutabilityBlame>) {
1168         match blame {
1169             None => {}
1170             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1171             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1172                 let let_span = self.tcx.hir.span(node_id);
1173                 if let ty::BindByValue(..) = self.local_binding_mode(node_id) {
1174                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(let_span) {
1175                         let (_, is_implicit_self) = self.local_ty(node_id);
1176                         if is_implicit_self && snippet != "self" {
1177                             // avoid suggesting `mut &self`.
1178                             return
1179                         }
1180                         db.span_label(
1181                             let_span,
1182                             format!("consider changing this to `mut {}`", snippet)
1183                         );
1184                     }
1185                 }
1186             }
1187             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1188                 let let_span = self.tcx.hir.span(node_id);
1189                 match self.local_binding_mode(node_id) {
1190                     ty::BindByReference(..) => {
1191                         let snippet = self.tcx.sess.codemap().span_to_snippet(let_span);
1192                         if let Ok(snippet) = snippet {
1193                             db.span_label(
1194                                 let_span,
1195                                 format!("consider changing this to `{}`",
1196                                          snippet.replace("ref ", "ref mut "))
1197                             );
1198                         }
1199                     }
1200                     ty::BindByValue(..) => {
1201                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1202                             if let Some(msg) =
1203                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1204                                 db.span_label(local_ty.span, msg);
1205                             }
1206                         }
1207                     }
1208                 }
1209             }
1210             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1211                 let node_id = match self.tcx.hir.as_local_node_id(field.did) {
1212                     Some(node_id) => node_id,
1213                     None => return
1214                 };
1215
1216                 if let hir_map::Node::NodeField(ref field) = self.tcx.hir.get(node_id) {
1217                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1218                         db.span_label(field.ty.span, msg);
1219                     }
1220                 }
1221             }
1222         }
1223     }
1224
1225     fn report_out_of_scope_escaping_closure_capture(&self,
1226                                                     err: &BckError<'tcx>,
1227                                                     capture_span: Span)
1228     {
1229         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1230
1231         let suggestion =
1232             match self.tcx.sess.codemap().span_to_snippet(err.span) {
1233                 Ok(string) => format!("move {}", string),
1234                 Err(_) => format!("move |<args>| <body>")
1235             };
1236
1237         struct_span_err!(self.tcx.sess, err.span, E0373,
1238                          "closure may outlive the current function, \
1239                           but it borrows {}, \
1240                           which is owned by the current function",
1241                          cmt_path_or_string)
1242             .span_label(capture_span,
1243                        format!("{} is borrowed here",
1244                                 cmt_path_or_string))
1245             .span_label(err.span,
1246                        format!("may outlive borrowed value {}",
1247                                 cmt_path_or_string))
1248             .span_suggestion(err.span,
1249                              &format!("to force the closure to take ownership of {} \
1250                                        (and any other referenced variables), \
1251                                        use the `move` keyword",
1252                                        cmt_path_or_string),
1253                              suggestion)
1254             .emit();
1255     }
1256
1257     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1258         match *region {
1259             ty::ReScope(scope) => {
1260                 Some(scope.span(self.tcx, &self.region_scope_tree).end_point())
1261             }
1262             _ => None
1263         }
1264     }
1265
1266     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'tcx>,
1267                                     error_span: &Span) {
1268         match err.cmt.note {
1269             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1270                 // If this is an `Fn` closure, it simply can't mutate upvars.
1271                 // If it's an `FnMut` closure, the original variable was declared immutable.
1272                 // We need to determine which is the case here.
1273                 let kind = match err.cmt.upvar().unwrap().cat {
1274                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1275                     _ => bug!()
1276                 };
1277                 if kind == ty::ClosureKind::Fn {
1278                     let closure_node_id =
1279                         self.tcx.hir.def_index_to_node_id(upvar_id.closure_expr_id);
1280                     db.span_help(self.tcx.hir.span(closure_node_id),
1281                                  "consider changing this closure to take \
1282                                   self by mutable reference");
1283                 }
1284             }
1285             _ => {
1286                 if let Categorization::Deref(..) = err.cmt.cat {
1287                     db.span_label(*error_span, "cannot borrow as mutable");
1288                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1289                     let span = self.tcx.hir.span(local_id);
1290                     if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(span) {
1291                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1292                             db.span_label(*error_span, "cannot reborrow mutably");
1293                             db.span_label(*error_span, "try removing `&mut` here");
1294                         } else {
1295                             db.span_label(*error_span, "cannot borrow mutably");
1296                         }
1297                     } else {
1298                         db.span_label(*error_span, "cannot borrow mutably");
1299                     }
1300                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1301                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1302                         db.span_label(*error_span,
1303                                       "cannot mutably borrow immutable field");
1304                     }
1305                 }
1306             }
1307         }
1308     }
1309     pub fn append_loan_path_to_string(&self,
1310                                       loan_path: &LoanPath<'tcx>,
1311                                       out: &mut String) {
1312         match loan_path.kind {
1313             LpUpvar(ty::UpvarId { var_id: id, closure_expr_id: _ }) => {
1314                 out.push_str(&self.tcx.hir.name(self.tcx.hir.hir_to_node_id(id)).as_str());
1315             }
1316             LpVar(id) => {
1317                 out.push_str(&self.tcx.hir.name(id).as_str());
1318             }
1319
1320             LpDowncast(ref lp_base, variant_def_id) => {
1321                 out.push('(');
1322                 self.append_loan_path_to_string(&lp_base, out);
1323                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1324                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1325                 out.push(')');
1326             }
1327
1328             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(fname))) => {
1329                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1330                 match fname {
1331                     mc::NamedField(fname) => {
1332                         out.push('.');
1333                         out.push_str(&fname.as_str());
1334                     }
1335                     mc::PositionalField(idx) => {
1336                         out.push('.');
1337                         out.push_str(&idx.to_string());
1338                     }
1339                 }
1340             }
1341
1342             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1343                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1344                 out.push_str("[..]");
1345             }
1346
1347             LpExtend(ref lp_base, _, LpDeref(_)) => {
1348                 out.push('*');
1349                 self.append_loan_path_to_string(&lp_base, out);
1350             }
1351         }
1352     }
1353
1354     pub fn append_autoderefd_loan_path_to_string(&self,
1355                                                  loan_path: &LoanPath<'tcx>,
1356                                                  out: &mut String) {
1357         match loan_path.kind {
1358             LpExtend(ref lp_base, _, LpDeref(_)) => {
1359                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1360                 // rules would normally allow users to omit the `*x`.
1361                 // So just serialize such paths to `x.f` or x[3]` respectively.
1362                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1363             }
1364
1365             LpDowncast(ref lp_base, variant_def_id) => {
1366                 out.push('(');
1367                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1368                 out.push(':');
1369                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1370                 out.push(')');
1371             }
1372
1373             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1374                 self.append_loan_path_to_string(loan_path, out)
1375             }
1376         }
1377     }
1378
1379     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1380         let mut result = String::new();
1381         self.append_loan_path_to_string(loan_path, &mut result);
1382         result
1383     }
1384
1385     pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1386         cmt.descriptive_string(self.tcx)
1387     }
1388
1389     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
1390         match opt_loan_path(cmt) {
1391             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1392             None => self.cmt_to_string(cmt),
1393         }
1394     }
1395 }
1396
1397 impl BitwiseOperator for LoanDataFlowOperator {
1398     #[inline]
1399     fn join(&self, succ: usize, pred: usize) -> usize {
1400         succ | pred // loans from both preds are in scope
1401     }
1402 }
1403
1404 impl DataFlowOperator for LoanDataFlowOperator {
1405     #[inline]
1406     fn initial_value(&self) -> bool {
1407         false // no loans in scope by default
1408     }
1409 }
1410
1411 impl<'tcx> fmt::Debug for InteriorKind {
1412     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1413         match *self {
1414             InteriorField(mc::NamedField(fld)) => write!(f, "{}", fld),
1415             InteriorField(mc::PositionalField(i)) => write!(f, "#{}", i),
1416             InteriorElement => write!(f, "[]"),
1417         }
1418     }
1419 }
1420
1421 impl<'tcx> fmt::Debug for Loan<'tcx> {
1422     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1423         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1424                self.index,
1425                self.loan_path,
1426                self.kind,
1427                self.gen_scope,
1428                self.kill_scope,
1429                self.restricted_paths)
1430     }
1431 }
1432
1433 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1434     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1435         match self.kind {
1436             LpVar(id) => {
1437                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_string(id)))
1438             }
1439
1440             LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
1441                 let s = ty::tls::with(|tcx| {
1442                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1443                     tcx.hir.node_to_string(var_node_id)
1444                 });
1445                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1446             }
1447
1448             LpDowncast(ref lp, variant_def_id) => {
1449                 let variant_str = if variant_def_id.is_local() {
1450                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1451                 } else {
1452                     format!("{:?}", variant_def_id)
1453                 };
1454                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1455             }
1456
1457             LpExtend(ref lp, _, LpDeref(_)) => {
1458                 write!(f, "{:?}.*", lp)
1459             }
1460
1461             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1462                 write!(f, "{:?}.{:?}", lp, interior)
1463             }
1464         }
1465     }
1466 }
1467
1468 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1469     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1470         match self.kind {
1471             LpVar(id) => {
1472                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir.node_to_user_string(id)))
1473             }
1474
1475             LpUpvar(ty::UpvarId{ var_id, closure_expr_id: _ }) => {
1476                 let s = ty::tls::with(|tcx| {
1477                     let var_node_id = tcx.hir.hir_to_node_id(var_id);
1478                     tcx.hir.node_to_string(var_node_id)
1479                 });
1480                 write!(f, "$({} captured by closure)", s)
1481             }
1482
1483             LpDowncast(ref lp, variant_def_id) => {
1484                 let variant_str = if variant_def_id.is_local() {
1485                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1486                 } else {
1487                     format!("{:?}", variant_def_id)
1488                 };
1489                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1490             }
1491
1492             LpExtend(ref lp, _, LpDeref(_)) => {
1493                 write!(f, "{}.*", lp)
1494             }
1495
1496             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1497                 write!(f, "{}.{:?}", lp, interior)
1498             }
1499         }
1500     }
1501 }