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::Node;
  25 use rustc::hir::map::blocks::FnLikeNode;
  26 use rustc::cfg;
  27 use rustc::middle::borrowck::{BorrowCheckResult, SignalledError};
  28 use rustc::hir::def_id::{DefId, LocalDefId};
  29 use rustc::middle::expr_use_visitor as euv;
  30 use rustc::middle::mem_categorization as mc;
  31 use rustc::middle::mem_categorization::Categorization;
  32 use rustc::middle::mem_categorization::ImmutabilityBlame;
  33 use rustc::middle::region;
  34 use rustc::middle::free_region::RegionRelations;
  35 use rustc::ty::{self, Ty, TyCtxt};
  36 use rustc::ty::query::Providers;
  37 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  38 use rustc_mir::util::suggest_ref_mut;
  39 use rustc::util::nodemap::FxHashSet;
  40
  41 use std::borrow::Cow;
  42 use std::cell::{Cell, RefCell};
  43 use std::fmt;
  44 use std::rc::Rc;
  45 use rustc_data_structures::sync::Lrc;
  46 use std::hash::{Hash, Hasher};
  47 use syntax::ast;
  48 use syntax_pos::{MultiSpan, Span};
  49 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
  50
  51 use rustc::hir;
  52 use rustc::hir::intravisit::{self, Visitor};
  53
  54 use dataflow::{DataFlowContext, BitwiseOperator, DataFlowOperator, KillFrom};
  55
  56 pub mod check_loans;
  57
  58 pub mod gather_loans;
  59
  60 pub mod move_data;
  61
  62 mod unused;
  63
  64 #[derive(Clone, Copy)]
  65 pub struct LoanDataFlowOperator;
  66
  67 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  68
  69 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  70     tcx.par_body_owners(|body_owner_def_id| {
  71         tcx.borrowck(body_owner_def_id);
  72     });
  73 }
  74
  75 pub fn provide(providers: &mut Providers) {
  76     *providers = Providers {
  77         borrowck,
  78         ..*providers
  79     };
  80 }
  81
  82 /// Collection of conclusions determined via borrow checker analyses.
  83 pub struct AnalysisData<'a, 'tcx: 'a> {
  84     pub all_loans: Vec<Loan<'tcx>>,
  85     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  86     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  87 }
  88
  89 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  90     -> Lrc<BorrowCheckResult>
  91 {
  92     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  93
  94     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  95
  96     let owner_id = tcx.hir().as_local_node_id(owner_def_id).unwrap();
  97
  98     match tcx.hir().get(owner_id) {
  99         Node::StructCtor(_) |
 100         Node::Variant(_) => {
 101             // We get invoked with anything that has MIR, but some of
 102             // those things (notably the synthesized constructors from
 103             // tuple structs/variants) do not have an associated body
 104             // and do not need borrowchecking.
 105             return Lrc::new(BorrowCheckResult {
 106                 used_mut_nodes: Default::default(),
 107                 signalled_any_error: SignalledError::NoErrorsSeen,
 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: Default::default(),
 124         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 125     };
 126
 127     // Eventually, borrowck will always read the MIR, but at the
 128     // moment we do not. So, for now, we always force MIR to be
 129     // constructed for a given fn, since this may result in errors
 130     // being reported and we want that to happen.
 131     //
 132     // Note that `mir_validated` is a "stealable" result; the
 133     // thief, `optimized_mir()`, forces borrowck, so we know that
 134     // is not yet stolen.
 135     ty::query::queries::mir_validated::ensure(tcx, owner_def_id);
 136
 137     // option dance because you can't capture an uninitialized variable
 138     // by mut-ref.
 139     let mut cfg = None;
 140     if let Some(AnalysisData { all_loans,
 141                                loans: loan_dfcx,
 142                                move_data: flowed_moves }) =
 143         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 144                                      |bccx| {
 145                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 146                                          cfg.as_mut().unwrap()
 147                                      })
 148     {
 149         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 150     }
 151
 152     if !tcx.use_mir_borrowck() {
 153         unused::check(&mut bccx, body);
 154     }
 155
 156     Lrc::new(BorrowCheckResult {
 157         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 158         signalled_any_error: bccx.signalled_any_error.into_inner(),
 159     })
 160 }
 161
 162 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 163                                                  force_analysis: bool,
 164                                                  body_id: hir::BodyId,
 165                                                  get_cfg: F)
 166                                                  -> Option<AnalysisData<'a, 'tcx>>
 167     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 168 {
 169     // Check the body of fn items.
 170     let tcx = this.tcx;
 171     let id_range = {
 172         let mut visitor = intravisit::IdRangeComputingVisitor::new(&tcx.hir());
 173         visitor.visit_body(this.body);
 174         visitor.result()
 175     };
 176     let (all_loans, move_data) =
 177         gather_loans::gather_loans_in_fn(this, body_id);
 178
 179     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 180         // large arrays of data inserted as constants can take a lot of
 181         // time and memory to borrow-check - see issue #36799. However,
 182         // they don't have places, so no borrow-check is actually needed.
 183         // Recognize that case and skip borrow-checking.
 184         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 185         return None;
 186     } else {
 187         debug!("propagating loans in {:?}", body_id);
 188     }
 189
 190     let cfg = get_cfg(this);
 191     let mut loan_dfcx =
 192         DataFlowContext::new(this.tcx,
 193                              "borrowck",
 194                              Some(this.body),
 195                              cfg,
 196                              LoanDataFlowOperator,
 197                              id_range,
 198                              all_loans.len());
 199     for (loan_idx, loan) in all_loans.iter().enumerate() {
 200         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 201         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 202                            loan.kill_scope.item_local_id(),
 203                            loan_idx);
 204     }
 205     loan_dfcx.add_kills_from_flow_exits(cfg);
 206     loan_dfcx.propagate(cfg, this.body);
 207
 208     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 209                                                       this,
 210                                                       cfg,
 211                                                       id_range,
 212                                                       this.body);
 213
 214     Some(AnalysisData { all_loans,
 215                         loans: loan_dfcx,
 216                         move_data:flowed_moves })
 217 }
 218
 219 /// Accessor for introspective clients inspecting `AnalysisData` and
 220 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 221 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 222     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 223     body_id: hir::BodyId,
 224     cfg: &cfg::CFG)
 225     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 226 {
 227     let owner_id = tcx.hir().body_owner(body_id);
 228     let owner_def_id = tcx.hir().local_def_id(owner_id);
 229     let tables = tcx.typeck_tables_of(owner_def_id);
 230     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 231     let body = tcx.hir().body(body_id);
 232     let mut bccx = BorrowckCtxt {
 233         tcx,
 234         tables,
 235         region_scope_tree,
 236         owner_def_id,
 237         body,
 238         used_mut_nodes: Default::default(),
 239         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 240     };
 241
 242     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 243     (bccx, dataflow_data.unwrap())
 244 }
 245
 246 // ----------------------------------------------------------------------
 247 // Type definitions
 248
 249 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 250     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 251
 252     // tables for the current thing we are checking; set to
 253     // Some in `borrowck_fn` and cleared later
 254     tables: &'a ty::TypeckTables<'tcx>,
 255
 256     region_scope_tree: Lrc<region::ScopeTree>,
 257
 258     owner_def_id: DefId,
 259
 260     body: &'tcx hir::Body,
 261
 262     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 263
 264     signalled_any_error: Cell<SignalledError>,
 265 }
 266
 267
 268 impl<'a, 'tcx: 'a> BorrowckCtxt<'a, 'tcx> {
 269     fn signal_error(&self) {
 270         self.signalled_any_error.set(SignalledError::SawSomeError);
 271     }
 272 }
 273
 274 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 275     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 276                                                      sp: S,
 277                                                      msg: &str,
 278                                                      code: DiagnosticId)
 279                                                      -> DiagnosticBuilder<'a>
 280     {
 281         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 282     }
 283
 284     fn struct_span_err<S: Into<MultiSpan>>(self,
 285                                            sp: S,
 286                                            msg: &str)
 287                                            -> DiagnosticBuilder<'a>
 288     {
 289         self.tcx.sess.struct_span_err(sp, msg)
 290     }
 291
 292     fn cancel_if_wrong_origin(self,
 293                               mut diag: DiagnosticBuilder<'a>,
 294                               o: Origin)
 295                               -> DiagnosticBuilder<'a>
 296     {
 297         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 298             self.tcx.sess.diagnostic().cancel(&mut diag);
 299         }
 300         diag
 301     }
 302 }
 303
 304 ///////////////////////////////////////////////////////////////////////////
 305 // Loans and loan paths
 306
 307 /// Record of a loan that was issued.
 308 pub struct Loan<'tcx> {
 309     index: usize,
 310     loan_path: Rc<LoanPath<'tcx>>,
 311     kind: ty::BorrowKind,
 312     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 313
 314     /// gen_scope indicates where loan is introduced. Typically the
 315     /// loan is introduced at the point of the borrow, but in some
 316     /// cases, notably method arguments, the loan may be introduced
 317     /// only later, once it comes into scope.  See also
 318     /// `GatherLoanCtxt::compute_gen_scope`.
 319     gen_scope: region::Scope,
 320
 321     /// kill_scope indicates when the loan goes out of scope.  This is
 322     /// either when the lifetime expires or when the local variable
 323     /// which roots the loan-path goes out of scope, whichever happens
 324     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 325     kill_scope: region::Scope,
 326     span: Span,
 327     cause: euv::LoanCause,
 328 }
 329
 330 impl<'tcx> Loan<'tcx> {
 331     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 332         self.loan_path.clone()
 333     }
 334 }
 335
 336 #[derive(Eq)]
 337 pub struct LoanPath<'tcx> {
 338     kind: LoanPathKind<'tcx>,
 339     ty: Ty<'tcx>,
 340 }
 341
 342 impl<'tcx> PartialEq for LoanPath<'tcx> {
 343     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 344         self.kind == that.kind
 345     }
 346 }
 347
 348 impl<'tcx> Hash for LoanPath<'tcx> {
 349     fn hash<H: Hasher>(&self, state: &mut H) {
 350         self.kind.hash(state);
 351     }
 352 }
 353
 354 #[derive(PartialEq, Eq, Hash, Debug)]
 355 pub enum LoanPathKind<'tcx> {
 356     LpVar(ast::NodeId),                         // `x` in README.md
 357     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 358     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 359     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 360 }
 361
 362 impl<'tcx> LoanPath<'tcx> {
 363     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 364         LoanPath { kind: kind, ty: ty }
 365     }
 366
 367     fn to_type(&self) -> Ty<'tcx> { self.ty }
 368
 369     fn has_downcast(&self) -> bool {
 370         match self.kind {
 371             LpDowncast(_, _) => true,
 372             LpExtend(ref lp, _, LpInterior(_, _)) => {
 373                 lp.has_downcast()
 374             }
 375             _ => false,
 376         }
 377     }
 378 }
 379
 380 // FIXME (pnkfelix): See discussion here
 381 // https://github.com/pnkfelix/rust/commit/
 382 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 383 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 384
 385 // A local, "cleaned" version of `mc::InteriorKind` that drops
 386 // information that is not relevant to loan-path analysis. (In
 387 // particular, the distinction between how precisely an array-element
 388 // is tracked is irrelevant here.)
 389 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 390 pub enum InteriorKind {
 391     InteriorField(mc::FieldIndex),
 392     InteriorElement,
 393 }
 394
 395 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 396 impl ToInteriorKind for mc::InteriorKind {
 397     fn cleaned(self) -> InteriorKind {
 398         match self {
 399             mc::InteriorField(name) => InteriorField(name),
 400             mc::InteriorElement(_) => InteriorElement,
 401         }
 402     }
 403 }
 404
 405 // This can be:
 406 // - a pointer dereference (`*P` in README.md)
 407 // - a field reference, with an optional definition of the containing
 408 //   enum variant (`P.f` in README.md)
 409 // `DefId` is present when the field is part of struct that is in
 410 // a variant of an enum. For instance in:
 411 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 412 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 413 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 414 pub enum LoanPathElem<'tcx> {
 415     LpDeref(mc::PointerKind<'tcx>),
 416     LpInterior(Option<DefId>, InteriorKind),
 417 }
 418
 419 fn closure_to_block(closure_id: LocalDefId,
 420                     tcx: TyCtxt) -> ast::NodeId {
 421     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 422     match tcx.hir().get(closure_id) {
 423         Node::Expr(expr) => match expr.node {
 424             hir::ExprKind::Closure(.., body_id, _, _) => {
 425                 body_id.node_id
 426             }
 427             _ => {
 428                 bug!("encountered non-closure id: {}", closure_id)
 429             }
 430         },
 431         _ => bug!("encountered non-expr id: {}", closure_id)
 432     }
 433 }
 434
 435 impl<'a, 'tcx> LoanPath<'tcx> {
 436     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 437         match self.kind {
 438             LpVar(local_id) => {
 439                 let hir_id = bccx.tcx.hir().node_to_hir_id(local_id);
 440                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 441             }
 442             LpUpvar(upvar_id) => {
 443                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 444                 let hir_id = bccx.tcx.hir().node_to_hir_id(block_id);
 445                 region::Scope { id: hir_id.local_id, data: region::ScopeData::Node }
 446             }
 447             LpDowncast(ref base, _) |
 448             LpExtend(ref base, ..) => base.kill_scope(bccx),
 449         }
 450     }
 451
 452     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 453         match (&self.kind, &other.kind) {
 454             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 455              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 456                 if id == id2 && opt_variant_id == opt_variant_id2 {
 457                     base.has_fork(&base2)
 458                 } else {
 459                     true
 460                 },
 461             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 462             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 463             _ => false,
 464         }
 465     }
 466
 467     fn depth(&self) -> usize {
 468         match self.kind {
 469             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 470             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 471             _ => 0,
 472         }
 473     }
 474
 475     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 476         match (&self.kind, &other.kind) {
 477             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 478              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 479                 if id == id2 && opt_variant_id == opt_variant_id2 {
 480                     base.common(&base2).map(|x| {
 481                         let xd = x.depth();
 482                         if base.depth() == xd && base2.depth() == xd {
 483                             LoanPath {
 484                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 485                                 ty: self.ty,
 486                             }
 487                         } else {
 488                             x
 489                         }
 490                     })
 491                 } else {
 492                     base.common(&base2)
 493                 }
 494             }
 495             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 496             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 497             (&LpVar(id), &LpVar(id2)) => {
 498                 if id == id2 {
 499                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 500                 } else {
 501                     None
 502                 }
 503             }
 504             (&LpUpvar(id), &LpUpvar(id2)) => {
 505                 if id == id2 {
 506                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 507                 } else {
 508                     None
 509                 }
 510             }
 511             _ => None,
 512         }
 513     }
 514 }
 515
 516 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 517 // mutable independently of the struct it belongs to. (#35937)
 518 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 519     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 520
 521     match cmt.cat {
 522         Categorization::Rvalue(..) |
 523         Categorization::ThreadLocal(..) |
 524         Categorization::StaticItem => {
 525             (None, false)
 526         }
 527
 528         Categorization::Local(id) => {
 529             (Some(new_lp(LpVar(id))), false)
 530         }
 531
 532         Categorization::Upvar(mc::Upvar { id, .. }) => {
 533             (Some(new_lp(LpUpvar(id))), false)
 534         }
 535
 536         Categorization::Deref(ref cmt_base, pk) => {
 537             let lp = opt_loan_path_is_field(cmt_base);
 538             (lp.0.map(|lp| {
 539                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 540             }), lp.1)
 541         }
 542
 543         Categorization::Interior(ref cmt_base, ik) => {
 544             (opt_loan_path(cmt_base).map(|lp| {
 545                 let opt_variant_id = match cmt_base.cat {
 546                     Categorization::Downcast(_, did) =>  Some(did),
 547                     _ => None
 548                 };
 549                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 550             }), true)
 551         }
 552
 553         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 554             let lp = opt_loan_path_is_field(cmt_base);
 555             (lp.0.map(|lp| {
 556                 new_lp(LpDowncast(lp, variant_def_id))
 557             }), lp.1)
 558         }
 559     }
 560 }
 561
 562 /// Computes the `LoanPath` (if any) for a `cmt`.
 563 /// Note that this logic is somewhat duplicated in
 564 /// the method `compute()` found in `gather_loans::restrictions`,
 565 /// which allows it to share common loan path pieces as it
 566 /// traverses the CMT.
 567 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 568     opt_loan_path_is_field(cmt).0
 569 }
 570
 571 ///////////////////////////////////////////////////////////////////////////
 572 // Errors
 573
 574 // Errors that can occur
 575 #[derive(Debug, PartialEq)]
 576 pub enum bckerr_code<'tcx> {
 577     err_mutbl,
 578     /// superscope, subscope, loan cause
 579     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 580     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 581 }
 582
 583 // Combination of an error code and the categorization of the expression
 584 // that caused it
 585 #[derive(Debug, PartialEq)]
 586 pub struct BckError<'c, 'tcx: 'c> {
 587     span: Span,
 588     cause: AliasableViolationKind,
 589     cmt: &'c mc::cmt_<'tcx>,
 590     code: bckerr_code<'tcx>
 591 }
 592
 593 #[derive(Copy, Clone, Debug, PartialEq)]
 594 pub enum AliasableViolationKind {
 595     MutabilityViolation,
 596     BorrowViolation(euv::LoanCause)
 597 }
 598
 599 #[derive(Copy, Clone, Debug)]
 600 pub enum MovedValueUseKind {
 601     MovedInUse,
 602     MovedInCapture,
 603 }
 604
 605 ///////////////////////////////////////////////////////////////////////////
 606 // Misc
 607
 608 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 609     pub fn is_subregion_of(&self,
 610                            r_sub: ty::Region<'tcx>,
 611                            r_sup: ty::Region<'tcx>)
 612                            -> bool
 613     {
 614         let region_rels = RegionRelations::new(self.tcx,
 615                                                self.owner_def_id,
 616                                                &self.region_scope_tree,
 617                                                &self.tables.free_region_map);
 618         region_rels.is_subregion_of(r_sub, r_sup)
 619     }
 620
 621     pub fn report(&self, err: BckError<'a, 'tcx>) {
 622         // Catch and handle some particular cases.
 623         match (&err.code, &err.cause) {
 624             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 625              &BorrowViolation(euv::ClosureCapture(span))) |
 626             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 627              &BorrowViolation(euv::ClosureCapture(span))) |
 628             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 629              &BorrowViolation(euv::ClosureCapture(span))) => {
 630                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 631             }
 632             _ => { }
 633         }
 634
 635         self.report_bckerr(&err);
 636     }
 637
 638     pub fn report_use_of_moved_value(&self,
 639                                      use_span: Span,
 640                                      use_kind: MovedValueUseKind,
 641                                      lp: &LoanPath<'tcx>,
 642                                      the_move: &move_data::Move,
 643                                      moved_lp: &LoanPath<'tcx>) {
 644         let (verb, verb_participle) = match use_kind {
 645             MovedInUse => ("use", "used"),
 646             MovedInCapture => ("capture", "captured"),
 647         };
 648
 649         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 650             move_data::Declared => {
 651                 // If this is an uninitialized variable, just emit a simple warning
 652                 // and return.
 653                 self.cannot_act_on_uninitialized_variable(use_span,
 654                                                           verb,
 655                                                           &self.loan_path_to_string(lp),
 656                                                           Origin::Ast)
 657                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 658                                                   self.loan_path_to_string(lp)))
 659                     .emit();
 660                 self.signal_error();
 661                 return;
 662             }
 663             _ => {
 664                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 665                 // normally generate a rather confusing message:
 666                 //
 667                 //     error: use of moved value: `x.b`
 668                 //     note: `x.a` moved here...
 669                 //
 670                 // What we want to do instead is get the 'common ancestor' of the two moves and
 671                 // use that for most of the message instead, giving is something like this:
 672                 //
 673                 //     error: use of moved value: `x`
 674                 //     note: `x` moved here (through moving `x.a`)...
 675
 676                 let common = moved_lp.common(lp);
 677                 let has_common = common.is_some();
 678                 let has_fork = moved_lp.has_fork(lp);
 679                 let (nl, ol, moved_lp_msg) =
 680                     if has_fork && has_common {
 681                         let nl = self.loan_path_to_string(&common.unwrap());
 682                         let ol = nl.clone();
 683                         let moved_lp_msg = format!(" (through moving `{}`)",
 684                                                    self.loan_path_to_string(moved_lp));
 685                         (nl, ol, moved_lp_msg)
 686                     } else {
 687                         (self.loan_path_to_string(lp),
 688                          self.loan_path_to_string(moved_lp),
 689                          String::new())
 690                     };
 691
 692                 let partial = moved_lp.depth() > lp.depth();
 693                 let msg = if !has_fork && partial { "partially " }
 694                           else if has_fork && !has_common { "collaterally "}
 695                 else { "" };
 696                 let mut err = self.cannot_act_on_moved_value(use_span,
 697                                                              verb,
 698                                                              msg,
 699                                                              Some(nl),
 700                                                              Origin::Ast);
 701                 let need_note = match lp.ty.sty {
 702                     ty::Closure(id, _) => {
 703                         let node_id = self.tcx.hir().as_local_node_id(id).unwrap();
 704                         let hir_id = self.tcx.hir().node_to_hir_id(node_id);
 705                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 706                             err.span_note(*span, &format!(
 707                                 "closure cannot be invoked more than once because \
 708                                 it moves the variable `{}` out of its environment",
 709                                 name
 710                             ));
 711                             false
 712                         } else {
 713                             true
 714                         }
 715                     }
 716                     _ => true,
 717                 };
 718                 (ol, moved_lp_msg, err, need_note)
 719             }
 720         };
 721
 722         // Get type of value and span where it was previously
 723         // moved.
 724         let node_id = self.tcx.hir().hir_to_node_id(hir::HirId {
 725             owner: self.body.value.hir_id.owner,
 726             local_id: the_move.id
 727         });
 728         let (move_span, move_note) = match the_move.kind {
 729             move_data::Declared => {
 730                 unreachable!();
 731             }
 732
 733             move_data::MoveExpr |
 734             move_data::MovePat => (self.tcx.hir().span(node_id), ""),
 735
 736             move_data::Captured =>
 737                 (match self.tcx.hir().expect_expr(node_id).node {
 738                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 739                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 740                                   the_move.id, r),
 741                 }, " (into closure)"),
 742         };
 743
 744         // Annotate the use and the move in the span. Watch out for
 745         // the case where the use and the move are the same. This
 746         // means the use is in a loop.
 747         err = if use_span == move_span {
 748             err.span_label(
 749                 use_span,
 750                 format!("value moved{} here in previous iteration of loop",
 751                          move_note));
 752             err
 753         } else {
 754             err.span_label(use_span, format!("value {} here after move", verb_participle));
 755             err.span_label(move_span, format!("value moved{} here", move_note));
 756             err
 757         };
 758
 759         if need_note {
 760             err.note(&format!(
 761                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 762                 if moved_lp.has_downcast() {
 763                     "the value".to_string()
 764                 } else {
 765                     format!("`{}`", self.loan_path_to_string(moved_lp))
 766                 },
 767                 moved_lp.ty));
 768         }
 769
 770         // Note: we used to suggest adding a `ref binding` or calling
 771         // `clone` but those suggestions have been removed because
 772         // they are often not what you actually want to do, and were
 773         // not considered particularly helpful.
 774
 775         err.emit();
 776         self.signal_error();
 777     }
 778
 779     pub fn report_partial_reinitialization_of_uninitialized_structure(
 780             &self,
 781             span: Span,
 782             lp: &LoanPath<'tcx>) {
 783         self.cannot_partially_reinit_an_uninit_struct(span,
 784                                                       &self.loan_path_to_string(lp),
 785                                                       Origin::Ast)
 786             .emit();
 787         self.signal_error();
 788     }
 789
 790     pub fn report_reassigned_immutable_variable(&self,
 791                                                 span: Span,
 792                                                 lp: &LoanPath<'tcx>,
 793                                                 assign:
 794                                                 &move_data::Assignment) {
 795         let mut err = self.cannot_reassign_immutable(span,
 796                                                      &self.loan_path_to_string(lp),
 797                                                      false,
 798                                                      Origin::Ast);
 799         err.span_label(span, "cannot assign twice to immutable variable");
 800         if span != assign.span {
 801             err.span_label(assign.span, format!("first assignment to `{}`",
 802                                                 self.loan_path_to_string(lp)));
 803         }
 804         err.emit();
 805         self.signal_error();
 806     }
 807
 808     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 809         let error_span = err.span.clone();
 810
 811         match err.code {
 812             err_mutbl => {
 813                 let descr: Cow<'static, str> = match err.cmt.note {
 814                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 815                         self.cmt_to_cow_str(&err.cmt)
 816                     }
 817                     _ => match opt_loan_path_is_field(&err.cmt) {
 818                         (None, true) => {
 819                             format!("{} of {} binding",
 820                                     self.cmt_to_cow_str(&err.cmt),
 821                                     err.cmt.mutbl.to_user_str()).into()
 822
 823                         }
 824                         (None, false) => {
 825                             format!("{} {}",
 826                                     err.cmt.mutbl.to_user_str(),
 827                                     self.cmt_to_cow_str(&err.cmt)).into()
 828
 829                         }
 830                         (Some(lp), true) => {
 831                             format!("{} `{}` of {} binding",
 832                                     self.cmt_to_cow_str(&err.cmt),
 833                                     self.loan_path_to_string(&lp),
 834                                     err.cmt.mutbl.to_user_str()).into()
 835                         }
 836                         (Some(lp), false) => {
 837                             format!("{} {} `{}`",
 838                                     err.cmt.mutbl.to_user_str(),
 839                                     self.cmt_to_cow_str(&err.cmt),
 840                                     self.loan_path_to_string(&lp)).into()
 841                         }
 842                     }
 843                 };
 844
 845                 let mut db = match err.cause {
 846                     MutabilityViolation => {
 847                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 848                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 849                             let node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
 850                             let sp = self.tcx.hir().span(node_id);
 851                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 852                                                   environment for modifications";
 853                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 854                                 (_, &Categorization::Upvar(mc::Upvar {
 855                                     kind: ty::ClosureKind::Fn, ..
 856                                 })) => {
 857                                     db.note(fn_closure_msg);
 858                                     // we should point at the cause for this closure being
 859                                     // identified as `Fn` (like in signature of method this
 860                                     // closure was passed into)
 861                                 }
 862                                 (Ok(ref snippet), ref cat) => {
 863                                     let msg = &format!("consider making `{}` mutable", snippet);
 864                                     let suggestion = format!("mut {}", snippet);
 865
 866                                     if let &Categorization::Deref(ref cmt, _) = cat {
 867                                         if let Categorization::Upvar(mc::Upvar {
 868                                             kind: ty::ClosureKind::Fn, ..
 869                                         }) = cmt.cat {
 870                                             db.note(fn_closure_msg);
 871                                         } else {
 872                                             db.span_suggestion_with_applicability(
 873                                                 sp,
 874                                                 msg,
 875                                                 suggestion,
 876                                                 Applicability::Unspecified,
 877                                             );
 878                                         }
 879                                     } else {
 880                                         db.span_suggestion_with_applicability(
 881                                             sp,
 882                                             msg,
 883                                             suggestion,
 884                                             Applicability::Unspecified,
 885                                         );
 886                                     }
 887                                 }
 888                                 _ => {
 889                                     db.span_help(sp, "consider making this binding mutable");
 890                                 }
 891                             }
 892                         }
 893
 894                         db
 895                     }
 896                     BorrowViolation(euv::ClosureCapture(_)) => {
 897                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 898                     }
 899                     BorrowViolation(euv::OverloadedOperator) |
 900                     BorrowViolation(euv::AddrOf) |
 901                     BorrowViolation(euv::RefBinding) |
 902                     BorrowViolation(euv::AutoRef) |
 903                     BorrowViolation(euv::AutoUnsafe) |
 904                     BorrowViolation(euv::ForLoop) |
 905                     BorrowViolation(euv::MatchDiscriminant) => {
 906                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 907                     }
 908                     BorrowViolation(euv::ClosureInvocation) => {
 909                         span_bug!(err.span,
 910                             "err_mutbl with a closure invocation");
 911                     }
 912                 };
 913
 914                 // We add a special note about `IndexMut`, if the source of this error
 915                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 916                 // to implement two traits for "one operator" is not very intuitive for
 917                 // many programmers.
 918                 if err.cmt.note == mc::NoteIndex {
 919                     let node_id = self.tcx.hir().hir_to_node_id(err.cmt.hir_id);
 920                     let node =  self.tcx.hir().get(node_id);
 921
 922                     // This pattern probably always matches.
 923                     if let Node::Expr(
 924                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 925                     ) = node {
 926                         let ty = self.tables.expr_ty(lhs);
 927
 928                         db.help(&format!(
 929                             "trait `IndexMut` is required to modify indexed content, but \
 930                              it is not implemented for `{}`",
 931                             ty
 932                         ));
 933                     }
 934                 }
 935
 936                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 937                 self.note_immutability_blame(
 938                     &mut db,
 939                     err.cmt.immutability_blame(),
 940                     self.tcx.hir().hir_to_node_id(err.cmt.hir_id)
 941                 );
 942                 db.emit();
 943                 self.signal_error();
 944             }
 945             err_out_of_scope(super_scope, sub_scope, cause) => {
 946                 let msg = match opt_loan_path(&err.cmt) {
 947                     None => "borrowed value".to_string(),
 948                     Some(lp) => {
 949                         format!("`{}`", self.loan_path_to_string(&lp))
 950                     }
 951                 };
 952
 953                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 954                 let value_kind = match err.cmt.cat {
 955                     mc::Categorization::Rvalue(..) => "temporary value",
 956                     _ => "borrowed value",
 957                 };
 958
 959                 let is_closure = match cause {
 960                     euv::ClosureCapture(s) => {
 961                         // The primary span starts out as the closure creation point.
 962                         // Change the primary span here to highlight the use of the variable
 963                         // in the closure, because it seems more natural. Highlight
 964                         // closure creation point as a secondary span.
 965                         match db.span.primary_span() {
 966                             Some(primary) => {
 967                                 db.span = MultiSpan::from_span(s);
 968                                 db.span_label(primary, "capture occurs here");
 969                                 db.span_label(s, format!("{} does not live long enough",
 970                                                          value_kind));
 971                                 true
 972                             }
 973                             None => false
 974                         }
 975                     }
 976                     _ => {
 977                         db.span_label(error_span, format!("{} does not live long enough",
 978                                                           value_kind));
 979                         false
 980                     }
 981                 };
 982
 983                 let sub_span = self.region_end_span(sub_scope);
 984                 let super_span = self.region_end_span(super_scope);
 985
 986                 match (sub_span, super_span) {
 987                     (Some(s1), Some(s2)) if s1 == s2 => {
 988                         if !is_closure {
 989                             let msg = match opt_loan_path(&err.cmt) {
 990                                 None => value_kind.to_string(),
 991                                 Some(lp) => {
 992                                     format!("`{}`", self.loan_path_to_string(&lp))
 993                                 }
 994                             };
 995                             db.span_label(s1,
 996                                           format!("{} dropped here while still borrowed", msg));
 997                         } else {
 998                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 999                         }
1000                         db.note("values in a scope are dropped in the opposite order \
1001                                 they are created");
1002                     }
1003                     (Some(s1), Some(s2)) if !is_closure => {
1004                         let msg = match opt_loan_path(&err.cmt) {
1005                             None => value_kind.to_string(),
1006                             Some(lp) => {
1007                                 format!("`{}`", self.loan_path_to_string(&lp))
1008                             }
1009                         };
1010                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
1011                         db.span_label(s1, format!("{} needs to live until here", value_kind));
1012                     }
1013                     _ => {
1014                         match sub_span {
1015                             Some(s) => {
1016                                 db.span_label(s, format!("{} needs to live until here",
1017                                                           value_kind));
1018                             }
1019                             None => {
1020                                 self.tcx.note_and_explain_region(
1021                                     &self.region_scope_tree,
1022                                     &mut db,
1023                                     "borrowed value must be valid for ",
1024                                     sub_scope,
1025                                     "...");
1026                             }
1027                         }
1028                         match super_span {
1029                             Some(s) => {
1030                                 db.span_label(s, format!("{} only lives until here", value_kind));
1031                             }
1032                             None => {
1033                                 self.tcx.note_and_explain_region(
1034                                     &self.region_scope_tree,
1035                                     &mut db,
1036                                     "...but borrowed value is only valid for ",
1037                                     super_scope,
1038                                     "");
1039                             }
1040                         }
1041                     }
1042                 }
1043
1044                 if let ty::ReScope(scope) = *super_scope {
1045                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1046                     match self.tcx.hir().find(node_id) {
1047                         Some(Node::Stmt(_)) => {
1048                             if *sub_scope != ty::ReStatic {
1049                                 db.note("consider using a `let` binding to increase its lifetime");
1050                             }
1051
1052                         }
1053                         _ => {}
1054                     }
1055                 }
1056
1057                 db.emit();
1058                 self.signal_error();
1059             }
1060             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1061                 let descr = self.cmt_to_path_or_string(err.cmt);
1062                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1063                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1064                     Some(lp) => {
1065                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1066                     }
1067                     None => self.cmt_to_cow_str(&err.cmt)
1068                 };
1069                 self.tcx.note_and_explain_region(
1070                     &self.region_scope_tree,
1071                     &mut db,
1072                     &format!("{} would have to be valid for ",
1073                             descr),
1074                     loan_scope,
1075                     "...");
1076                 self.tcx.note_and_explain_region(
1077                     &self.region_scope_tree,
1078                     &mut db,
1079                     &format!("...but {} is only valid for ", descr),
1080                     ptr_scope,
1081                     "");
1082
1083                 db.emit();
1084                 self.signal_error();
1085             }
1086         }
1087     }
1088
1089     pub fn report_aliasability_violation(&self,
1090                                          span: Span,
1091                                          kind: AliasableViolationKind,
1092                                          cause: mc::AliasableReason,
1093                                          cmt: &mc::cmt_<'tcx>) {
1094         let mut is_closure = false;
1095         let prefix = match kind {
1096             MutabilityViolation => {
1097                 "cannot assign to data"
1098             }
1099             BorrowViolation(euv::ClosureCapture(_)) |
1100             BorrowViolation(euv::OverloadedOperator) |
1101             BorrowViolation(euv::AddrOf) |
1102             BorrowViolation(euv::AutoRef) |
1103             BorrowViolation(euv::AutoUnsafe) |
1104             BorrowViolation(euv::RefBinding) |
1105             BorrowViolation(euv::MatchDiscriminant) => {
1106                 "cannot borrow data mutably"
1107             }
1108
1109             BorrowViolation(euv::ClosureInvocation) => {
1110                 is_closure = true;
1111                 "closure invocation"
1112             }
1113
1114             BorrowViolation(euv::ForLoop) => {
1115                 "`for` loop"
1116             }
1117         };
1118
1119         match cause {
1120             mc::AliasableStaticMut => {
1121                 // This path cannot occur. `static mut X` is not checked
1122                 // for aliasability violations.
1123                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1124             }
1125             mc::AliasableStatic | mc::AliasableBorrowed => {}
1126         };
1127         let blame = cmt.immutability_blame();
1128         let mut err = match blame {
1129             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1130                 // FIXME: the distinction between these 2 messages looks wrong.
1131                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1132                     // The aliasability violation with closure captures can
1133                     // happen for nested closures, so we know the enclosing
1134                     // closure incorrectly accepts an `Fn` while it needs to
1135                     // be `FnMut`.
1136                     "consider changing this to accept closures that implement `FnMut`"
1137
1138                 } else {
1139                     "consider changing this closure to take self by mutable reference"
1140                 };
1141                 let node_id = self.tcx.hir().local_def_id_to_node_id(id);
1142                 let help_span = self.tcx.hir().span(node_id);
1143                 self.cannot_act_on_capture_in_sharable_fn(span,
1144                                                           prefix,
1145                                                           (help_span, help_msg),
1146                                                           Origin::Ast)
1147             }
1148             _ =>  {
1149                 self.cannot_assign_into_immutable_reference(span, prefix,
1150                                                             Origin::Ast)
1151             }
1152         };
1153         self.note_immutability_blame(
1154             &mut err,
1155             blame,
1156             self.tcx.hir().hir_to_node_id(cmt.hir_id)
1157         );
1158
1159         if is_closure {
1160             err.help("closures behind references must be called via `&mut`");
1161         }
1162         err.emit();
1163         self.signal_error();
1164     }
1165
1166     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1167     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1168         // Check whether the argument is an immutable reference
1169         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1170         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1171             mutbl: hir::Mutability::MutImmutable,
1172             ref ty
1173         }) = pty.node {
1174             // Account for existing lifetimes when generating the message
1175             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1176                 Ok(snippet) => snippet,
1177                 _ => return None
1178             };
1179
1180             let lifetime_snippet = if !lifetime.is_elided() {
1181                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1182                     Ok(lifetime_snippet) => lifetime_snippet,
1183                     _ => return None
1184                 })
1185             } else {
1186                 String::new()
1187             };
1188             Some(format!("use `&{}mut {}` here to make mutable",
1189                          lifetime_snippet,
1190                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1191         } else {
1192             None
1193         }
1194     }
1195
1196     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1197         let pat = match self.tcx.hir().get(node_id) {
1198             Node::Binding(pat) => pat,
1199             node => bug!("bad node for local: {:?}", node)
1200         };
1201
1202         match pat.node {
1203             hir::PatKind::Binding(..) => {
1204                 *self.tables
1205                      .pat_binding_modes()
1206                      .get(pat.hir_id)
1207                      .expect("missing binding mode")
1208             }
1209             _ => bug!("local is not a binding: {:?}", pat)
1210         }
1211     }
1212
1213     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1214         let parent = self.tcx.hir().get_parent_node(node_id);
1215         let parent_node = self.tcx.hir().get(parent);
1216
1217         // The parent node is like a fn
1218         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1219             // `nid`'s parent's `Body`
1220             let fn_body = self.tcx.hir().body(fn_like.body());
1221             // Get the position of `node_id` in the arguments list
1222             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1223             if let Some(i) = arg_pos {
1224                 // The argument's `Ty`
1225                 (Some(&fn_like.decl().inputs[i]),
1226                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1227             } else {
1228                 (None, false)
1229             }
1230         } else {
1231             (None, false)
1232         }
1233     }
1234
1235     fn note_immutability_blame(&self,
1236                                db: &mut DiagnosticBuilder,
1237                                blame: Option<ImmutabilityBlame>,
1238                                error_node_id: ast::NodeId) {
1239         match blame {
1240             None => {}
1241             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1242             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1243                 self.note_immutable_local(db, error_node_id, node_id)
1244             }
1245             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1246                 match self.local_binding_mode(node_id) {
1247                     ty::BindByReference(..) => {
1248                         let let_span = self.tcx.hir().span(node_id);
1249                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1250                         if let Some(replace_str) = suggestion {
1251                             db.span_suggestion_with_applicability(
1252                                 let_span,
1253                                 "use a mutable reference instead",
1254                                 replace_str,
1255                                 // I believe this can be machine applicable,
1256                                 // but if there are multiple attempted uses of an immutable
1257                                 // reference, I don't know how rustfix handles it, it might
1258                                 // attempt fixing them multiple times.
1259                                 //                              @estebank
1260                                 Applicability::Unspecified,
1261                             );
1262                         }
1263                     }
1264                     ty::BindByValue(..) => {
1265                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1266                             if let Some(msg) =
1267                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1268                                 db.span_label(local_ty.span, msg);
1269                             }
1270                         }
1271                     }
1272                 }
1273             }
1274             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1275                 let node_id = match self.tcx.hir().as_local_node_id(field.did) {
1276                     Some(node_id) => node_id,
1277                     None => return
1278                 };
1279
1280                 if let Node::Field(ref field) = self.tcx.hir().get(node_id) {
1281                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1282                         db.span_label(field.ty.span, msg);
1283                     }
1284                 }
1285             }
1286         }
1287     }
1288
1289      // Suggest a fix when trying to mutably borrow an immutable local
1290      // binding: either to make the binding mutable (if its type is
1291      // not a mutable reference) or to avoid borrowing altogether
1292     fn note_immutable_local(&self,
1293                             db: &mut DiagnosticBuilder,
1294                             borrowed_node_id: ast::NodeId,
1295                             binding_node_id: ast::NodeId) {
1296         let let_span = self.tcx.hir().span(binding_node_id);
1297         if let ty::BindByValue(..) = self.local_binding_mode(binding_node_id) {
1298             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1299                 let (ty, is_implicit_self) = self.local_ty(binding_node_id);
1300                 if is_implicit_self && snippet != "self" {
1301                     // avoid suggesting `mut &self`.
1302                     return
1303                 }
1304                 if let Some(&hir::TyKind::Rptr(
1305                     _,
1306                     hir::MutTy {
1307                         mutbl: hir::MutMutable,
1308                         ..
1309                     },
1310                 )) = ty.map(|t| &t.node)
1311                 {
1312                     let borrow_expr_id = self.tcx.hir().get_parent_node(borrowed_node_id);
1313                     db.span_suggestion_with_applicability(
1314                         self.tcx.hir().span(borrow_expr_id),
1315                         "consider removing the `&mut`, as it is an \
1316                         immutable binding to a mutable reference",
1317                         snippet,
1318                         Applicability::MachineApplicable,
1319                     );
1320                 } else {
1321                     db.span_suggestion_with_applicability(
1322                         let_span,
1323                         "make this binding mutable",
1324                         format!("mut {}", snippet),
1325                         Applicability::MachineApplicable,
1326                     );
1327                 }
1328             }
1329         }
1330     }
1331
1332     fn report_out_of_scope_escaping_closure_capture(&self,
1333                                                     err: &BckError<'a, 'tcx>,
1334                                                     capture_span: Span)
1335     {
1336         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1337
1338         let suggestion =
1339             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1340                 Ok(string) => format!("move {}", string),
1341                 Err(_) => "move |<args>| <body>".to_string()
1342             };
1343
1344         self.cannot_capture_in_long_lived_closure(err.span,
1345                                                   &cmt_path_or_string,
1346                                                   capture_span,
1347                                                   Origin::Ast)
1348             .span_suggestion_with_applicability(
1349                  err.span,
1350                  &format!("to force the closure to take ownership of {} \
1351                            (and any other referenced variables), \
1352                            use the `move` keyword",
1353                            cmt_path_or_string),
1354                  suggestion,
1355                  Applicability::MachineApplicable,
1356             )
1357             .emit();
1358         self.signal_error();
1359     }
1360
1361     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1362         match *region {
1363             ty::ReScope(scope) => {
1364                 Some(self.tcx.sess.source_map().end_point(
1365                         scope.span(self.tcx, &self.region_scope_tree)))
1366             }
1367             _ => None
1368         }
1369     }
1370
1371     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder, err: &BckError<'a, 'tcx>,
1372                                     error_span: &Span) {
1373         match err.cmt.note {
1374             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1375                 // If this is an `Fn` closure, it simply can't mutate upvars.
1376                 // If it's an `FnMut` closure, the original variable was declared immutable.
1377                 // We need to determine which is the case here.
1378                 let kind = match err.cmt.upvar_cat().unwrap() {
1379                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1380                     _ => bug!()
1381                 };
1382                 if *kind == ty::ClosureKind::Fn {
1383                     let closure_node_id =
1384                         self.tcx.hir().local_def_id_to_node_id(upvar_id.closure_expr_id);
1385                     db.span_help(self.tcx.hir().span(closure_node_id),
1386                                  "consider changing this closure to take \
1387                                   self by mutable reference");
1388                 }
1389             }
1390             _ => {
1391                 if let Categorization::Deref(..) = err.cmt.cat {
1392                     db.span_label(*error_span, "cannot borrow as mutable");
1393                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1394                     let span = self.tcx.hir().span(local_id);
1395                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1396                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1397                             db.span_label(*error_span, "cannot reborrow mutably");
1398                             db.span_label(*error_span, "try removing `&mut` here");
1399                         } else {
1400                             db.span_label(*error_span, "cannot borrow mutably");
1401                         }
1402                     } else {
1403                         db.span_label(*error_span, "cannot borrow mutably");
1404                     }
1405                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1406                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1407                         db.span_label(*error_span,
1408                                       "cannot mutably borrow field of immutable binding");
1409                     }
1410                 }
1411             }
1412         }
1413     }
1414     pub fn append_loan_path_to_string(&self,
1415                                       loan_path: &LoanPath<'tcx>,
1416                                       out: &mut String) {
1417         match loan_path.kind {
1418             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id}, closure_expr_id: _ }) => {
1419                 out.push_str(&self.tcx.hir().name(self.tcx.hir().hir_to_node_id(id)).as_str());
1420             }
1421             LpVar(id) => {
1422                 out.push_str(&self.tcx.hir().name(id).as_str());
1423             }
1424
1425             LpDowncast(ref lp_base, variant_def_id) => {
1426                 out.push('(');
1427                 self.append_loan_path_to_string(&lp_base, out);
1428                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1429                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1430                 out.push(')');
1431             }
1432
1433             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1434                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1435                 out.push('.');
1436                 out.push_str(&info.as_str());
1437             }
1438
1439             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1440                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1441                 out.push_str("[..]");
1442             }
1443
1444             LpExtend(ref lp_base, _, LpDeref(_)) => {
1445                 out.push('*');
1446                 self.append_loan_path_to_string(&lp_base, out);
1447             }
1448         }
1449     }
1450
1451     pub fn append_autoderefd_loan_path_to_string(&self,
1452                                                  loan_path: &LoanPath<'tcx>,
1453                                                  out: &mut String) {
1454         match loan_path.kind {
1455             LpExtend(ref lp_base, _, LpDeref(_)) => {
1456                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1457                 // rules would normally allow users to omit the `*x`.
1458                 // So just serialize such paths to `x.f` or x[3]` respectively.
1459                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1460             }
1461
1462             LpDowncast(ref lp_base, variant_def_id) => {
1463                 out.push('(');
1464                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1465                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1466                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1467                 out.push(')');
1468             }
1469
1470             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1471                 self.append_loan_path_to_string(loan_path, out)
1472             }
1473         }
1474     }
1475
1476     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1477         let mut result = String::new();
1478         self.append_loan_path_to_string(loan_path, &mut result);
1479         result
1480     }
1481
1482     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1483         cmt.descriptive_string(self.tcx)
1484     }
1485
1486     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1487         match opt_loan_path(cmt) {
1488             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1489             None => self.cmt_to_cow_str(cmt).into_owned(),
1490         }
1491     }
1492 }
1493
1494 impl BitwiseOperator for LoanDataFlowOperator {
1495     #[inline]
1496     fn join(&self, succ: usize, pred: usize) -> usize {
1497         succ | pred // loans from both preds are in scope
1498     }
1499 }
1500
1501 impl DataFlowOperator for LoanDataFlowOperator {
1502     #[inline]
1503     fn initial_value(&self) -> bool {
1504         false // no loans in scope by default
1505     }
1506 }
1507
1508 impl<'tcx> fmt::Debug for InteriorKind {
1509     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1510         match *self {
1511             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1512             InteriorElement => write!(f, "[]"),
1513         }
1514     }
1515 }
1516
1517 impl<'tcx> fmt::Debug for Loan<'tcx> {
1518     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1519         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1520                self.index,
1521                self.loan_path,
1522                self.kind,
1523                self.gen_scope,
1524                self.kill_scope,
1525                self.restricted_paths)
1526     }
1527 }
1528
1529 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1530     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1531         match self.kind {
1532             LpVar(id) => {
1533                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().node_to_string(id)))
1534             }
1535
1536             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1537                 let s = ty::tls::with(|tcx| {
1538                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1539                     tcx.hir().node_to_string(var_node_id)
1540                 });
1541                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1542             }
1543
1544             LpDowncast(ref lp, variant_def_id) => {
1545                 let variant_str = if variant_def_id.is_local() {
1546                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1547                 } else {
1548                     format!("{:?}", variant_def_id)
1549                 };
1550                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1551             }
1552
1553             LpExtend(ref lp, _, LpDeref(_)) => {
1554                 write!(f, "{:?}.*", lp)
1555             }
1556
1557             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1558                 write!(f, "{:?}.{:?}", lp, interior)
1559             }
1560         }
1561     }
1562 }
1563
1564 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1565     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1566         match self.kind {
1567             LpVar(id) => {
1568                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().node_to_user_string(id)))
1569             }
1570
1571             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1572                 let s = ty::tls::with(|tcx| {
1573                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1574                     tcx.hir().node_to_string(var_node_id)
1575                 });
1576                 write!(f, "$({} captured by closure)", s)
1577             }
1578
1579             LpDowncast(ref lp, variant_def_id) => {
1580                 let variant_str = if variant_def_id.is_local() {
1581                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1582                 } else {
1583                     format!("{:?}", variant_def_id)
1584                 };
1585                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1586             }
1587
1588             LpExtend(ref lp, _, LpDeref(_)) => {
1589                 write!(f, "{}.*", lp)
1590             }
1591
1592             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1593                 write!(f, "{}.{:?}", lp, interior)
1594             }
1595         }
1596     }
1597 }