src/librustc_borrowck/borrowck/mod.rs

   1 //! See The Book chapter on the borrow checker for more details.
   2
   3 #![allow(non_camel_case_types)]
   4
   5 pub use LoanPathKind::*;
   6 pub use LoanPathElem::*;
   7 pub use bckerr_code::*;
   8 pub use AliasableViolationKind::*;
   9 pub use MovedValueUseKind::*;
  10
  11 use InteriorKind::*;
  12
  13 use rustc::hir::HirId;
  14 use rustc::hir::Node;
  15 use rustc::hir::map::blocks::FnLikeNode;
  16 use rustc::cfg;
  17 use rustc::middle::borrowck::{BorrowCheckResult, SignalledError};
  18 use rustc::hir::def_id::{DefId, LocalDefId};
  19 use rustc::middle::expr_use_visitor as euv;
  20 use rustc::middle::mem_categorization as mc;
  21 use rustc::middle::mem_categorization::Categorization;
  22 use rustc::middle::mem_categorization::ImmutabilityBlame;
  23 use rustc::middle::region;
  24 use rustc::middle::free_region::RegionRelations;
  25 use rustc::ty::{self, Ty, TyCtxt};
  26 use rustc::ty::query::Providers;
  27 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  28 use rustc_mir::util::suggest_ref_mut;
  29 use rustc::util::nodemap::FxHashSet;
  30
  31 use std::borrow::Cow;
  32 use std::cell::{Cell, RefCell};
  33 use std::fmt;
  34 use std::rc::Rc;
  35 use rustc_data_structures::sync::Lrc;
  36 use std::hash::{Hash, Hasher};
  37 use syntax::ast;
  38 use syntax_pos::{MultiSpan, Span};
  39 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
  40 use log::debug;
  41
  42 use rustc::hir;
  43
  44 use crate::dataflow::{DataFlowContext, BitwiseOperator, DataFlowOperator, KillFrom};
  45
  46 pub mod check_loans;
  47
  48 pub mod gather_loans;
  49
  50 pub mod move_data;
  51
  52 mod unused;
  53
  54 #[derive(Clone, Copy)]
  55 pub struct LoanDataFlowOperator;
  56
  57 pub type LoanDataFlow<'a, 'tcx> = DataFlowContext<'a, 'tcx, LoanDataFlowOperator>;
  58
  59 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
  60     tcx.par_body_owners(|body_owner_def_id| {
  61         tcx.ensure().borrowck(body_owner_def_id);
  62     });
  63 }
  64
  65 pub fn provide(providers: &mut Providers<'_>) {
  66     *providers = Providers {
  67         borrowck,
  68         ..*providers
  69     };
  70 }
  71
  72 /// Collection of conclusions determined via borrow checker analyses.
  73 pub struct AnalysisData<'a, 'tcx: 'a> {
  74     pub all_loans: Vec<Loan<'tcx>>,
  75     pub loans: DataFlowContext<'a, 'tcx, LoanDataFlowOperator>,
  76     pub move_data: move_data::FlowedMoveData<'a, 'tcx>,
  77 }
  78
  79 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
  80     -> Lrc<BorrowCheckResult>
  81 {
  82     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
  83
  84     debug!("borrowck(body_owner_def_id={:?})", owner_def_id);
  85
  86     let owner_id = tcx.hir().as_local_node_id(owner_def_id).unwrap();
  87
  88     match tcx.hir().get(owner_id) {
  89         Node::StructCtor(_) |
  90         Node::Variant(_) => {
  91             // We get invoked with anything that has MIR, but some of
  92             // those things (notably the synthesized constructors from
  93             // tuple structs/variants) do not have an associated body
  94             // and do not need borrowchecking.
  95             return Lrc::new(BorrowCheckResult {
  96                 used_mut_nodes: Default::default(),
  97                 signalled_any_error: SignalledError::NoErrorsSeen,
  98             })
  99         }
 100         _ => { }
 101     }
 102
 103     let body_id = tcx.hir().body_owned_by(owner_id);
 104     let tables = tcx.typeck_tables_of(owner_def_id);
 105     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 106     let body = tcx.hir().body(body_id);
 107     let mut bccx = BorrowckCtxt {
 108         tcx,
 109         tables,
 110         region_scope_tree,
 111         owner_def_id,
 112         body,
 113         used_mut_nodes: Default::default(),
 114         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 115     };
 116
 117     // Eventually, borrowck will always read the MIR, but at the
 118     // moment we do not. So, for now, we always force MIR to be
 119     // constructed for a given fn, since this may result in errors
 120     // being reported and we want that to happen.
 121     //
 122     // Note that `mir_validated` is a "stealable" result; the
 123     // thief, `optimized_mir()`, forces borrowck, so we know that
 124     // is not yet stolen.
 125     tcx.ensure().mir_validated(owner_def_id);
 126
 127     // option dance because you can't capture an uninitialized variable
 128     // by mut-ref.
 129     let mut cfg = None;
 130     if let Some(AnalysisData { all_loans,
 131                                loans: loan_dfcx,
 132                                move_data: flowed_moves }) =
 133         build_borrowck_dataflow_data(&mut bccx, false, body_id,
 134                                      |bccx| {
 135                                          cfg = Some(cfg::CFG::new(bccx.tcx, &body));
 136                                          cfg.as_mut().unwrap()
 137                                      })
 138     {
 139         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
 140     }
 141
 142     if !tcx.use_mir_borrowck() {
 143         unused::check(&mut bccx, body);
 144     }
 145
 146     Lrc::new(BorrowCheckResult {
 147         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
 148         signalled_any_error: bccx.signalled_any_error.into_inner(),
 149     })
 150 }
 151
 152 fn build_borrowck_dataflow_data<'a, 'c, 'tcx, F>(this: &mut BorrowckCtxt<'a, 'tcx>,
 153                                                  force_analysis: bool,
 154                                                  body_id: hir::BodyId,
 155                                                  get_cfg: F)
 156                                                  -> Option<AnalysisData<'a, 'tcx>>
 157     where F: FnOnce(&mut BorrowckCtxt<'a, 'tcx>) -> &'c cfg::CFG
 158 {
 159     // Check the body of fn items.
 160     let (all_loans, move_data) =
 161         gather_loans::gather_loans_in_fn(this, body_id);
 162
 163     if !force_analysis && move_data.is_empty() && all_loans.is_empty() {
 164         // large arrays of data inserted as constants can take a lot of
 165         // time and memory to borrow-check - see issue #36799. However,
 166         // they don't have places, so no borrow-check is actually needed.
 167         // Recognize that case and skip borrow-checking.
 168         debug!("skipping loan propagation for {:?} because of no loans", body_id);
 169         return None;
 170     } else {
 171         debug!("propagating loans in {:?}", body_id);
 172     }
 173
 174     let cfg = get_cfg(this);
 175     let mut loan_dfcx =
 176         DataFlowContext::new(this.tcx,
 177                              "borrowck",
 178                              Some(this.body),
 179                              cfg,
 180                              LoanDataFlowOperator,
 181                              all_loans.len());
 182     for (loan_idx, loan) in all_loans.iter().enumerate() {
 183         loan_dfcx.add_gen(loan.gen_scope.item_local_id(), loan_idx);
 184         loan_dfcx.add_kill(KillFrom::ScopeEnd,
 185                            loan.kill_scope.item_local_id(),
 186                            loan_idx);
 187     }
 188     loan_dfcx.add_kills_from_flow_exits(cfg);
 189     loan_dfcx.propagate(cfg, this.body);
 190
 191     let flowed_moves = move_data::FlowedMoveData::new(move_data,
 192                                                       this,
 193                                                       cfg,
 194                                                       this.body);
 195
 196     Some(AnalysisData { all_loans,
 197                         loans: loan_dfcx,
 198                         move_data:flowed_moves })
 199 }
 200
 201 /// Accessor for introspective clients inspecting `AnalysisData` and
 202 /// the `BorrowckCtxt` itself , e.g., the flowgraph visualizer.
 203 pub fn build_borrowck_dataflow_data_for_fn<'a, 'tcx>(
 204     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 205     body_id: hir::BodyId,
 206     cfg: &cfg::CFG)
 207     -> (BorrowckCtxt<'a, 'tcx>, AnalysisData<'a, 'tcx>)
 208 {
 209     let owner_id = tcx.hir().body_owner(body_id);
 210     let owner_def_id = tcx.hir().local_def_id(owner_id);
 211     let tables = tcx.typeck_tables_of(owner_def_id);
 212     let region_scope_tree = tcx.region_scope_tree(owner_def_id);
 213     let body = tcx.hir().body(body_id);
 214     let mut bccx = BorrowckCtxt {
 215         tcx,
 216         tables,
 217         region_scope_tree,
 218         owner_def_id,
 219         body,
 220         used_mut_nodes: Default::default(),
 221         signalled_any_error: Cell::new(SignalledError::NoErrorsSeen),
 222     };
 223
 224     let dataflow_data = build_borrowck_dataflow_data(&mut bccx, true, body_id, |_| cfg);
 225     (bccx, dataflow_data.unwrap())
 226 }
 227
 228 // ----------------------------------------------------------------------
 229 // Type definitions
 230
 231 pub struct BorrowckCtxt<'a, 'tcx: 'a> {
 232     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 233
 234     // tables for the current thing we are checking; set to
 235     // Some in `borrowck_fn` and cleared later
 236     tables: &'a ty::TypeckTables<'tcx>,
 237
 238     region_scope_tree: Lrc<region::ScopeTree>,
 239
 240     owner_def_id: DefId,
 241
 242     body: &'tcx hir::Body,
 243
 244     used_mut_nodes: RefCell<FxHashSet<HirId>>,
 245
 246     signalled_any_error: Cell<SignalledError>,
 247 }
 248
 249
 250 impl<'a, 'tcx: 'a> BorrowckCtxt<'a, 'tcx> {
 251     fn signal_error(&self) {
 252         self.signalled_any_error.set(SignalledError::SawSomeError);
 253     }
 254 }
 255
 256 impl<'a, 'b, 'tcx: 'b> BorrowckErrors<'a> for &'a BorrowckCtxt<'b, 'tcx> {
 257     fn struct_span_err_with_code<S: Into<MultiSpan>>(self,
 258                                                      sp: S,
 259                                                      msg: &str,
 260                                                      code: DiagnosticId)
 261                                                      -> DiagnosticBuilder<'a>
 262     {
 263         self.tcx.sess.struct_span_err_with_code(sp, msg, code)
 264     }
 265
 266     fn struct_span_err<S: Into<MultiSpan>>(self,
 267                                            sp: S,
 268                                            msg: &str)
 269                                            -> DiagnosticBuilder<'a>
 270     {
 271         self.tcx.sess.struct_span_err(sp, msg)
 272     }
 273
 274     fn cancel_if_wrong_origin(self,
 275                               mut diag: DiagnosticBuilder<'a>,
 276                               o: Origin)
 277                               -> DiagnosticBuilder<'a>
 278     {
 279         if !o.should_emit_errors(self.tcx.borrowck_mode()) {
 280             self.tcx.sess.diagnostic().cancel(&mut diag);
 281         }
 282         diag
 283     }
 284 }
 285
 286 ///////////////////////////////////////////////////////////////////////////
 287 // Loans and loan paths
 288
 289 /// Record of a loan that was issued.
 290 pub struct Loan<'tcx> {
 291     index: usize,
 292     loan_path: Rc<LoanPath<'tcx>>,
 293     kind: ty::BorrowKind,
 294     restricted_paths: Vec<Rc<LoanPath<'tcx>>>,
 295
 296     /// gen_scope indicates where loan is introduced. Typically the
 297     /// loan is introduced at the point of the borrow, but in some
 298     /// cases, notably method arguments, the loan may be introduced
 299     /// only later, once it comes into scope. See also
 300     /// `GatherLoanCtxt::compute_gen_scope`.
 301     gen_scope: region::Scope,
 302
 303     /// kill_scope indicates when the loan goes out of scope. This is
 304     /// either when the lifetime expires or when the local variable
 305     /// which roots the loan-path goes out of scope, whichever happens
 306     /// faster. See also `GatherLoanCtxt::compute_kill_scope`.
 307     kill_scope: region::Scope,
 308     span: Span,
 309     cause: euv::LoanCause,
 310 }
 311
 312 impl<'tcx> Loan<'tcx> {
 313     pub fn loan_path(&self) -> Rc<LoanPath<'tcx>> {
 314         self.loan_path.clone()
 315     }
 316 }
 317
 318 #[derive(Eq)]
 319 pub struct LoanPath<'tcx> {
 320     kind: LoanPathKind<'tcx>,
 321     ty: Ty<'tcx>,
 322 }
 323
 324 impl<'tcx> PartialEq for LoanPath<'tcx> {
 325     fn eq(&self, that: &LoanPath<'tcx>) -> bool {
 326         self.kind == that.kind
 327     }
 328 }
 329
 330 impl<'tcx> Hash for LoanPath<'tcx> {
 331     fn hash<H: Hasher>(&self, state: &mut H) {
 332         self.kind.hash(state);
 333     }
 334 }
 335
 336 #[derive(PartialEq, Eq, Hash, Debug)]
 337 pub enum LoanPathKind<'tcx> {
 338     LpVar(ast::NodeId),                         // `x` in README.md
 339     LpUpvar(ty::UpvarId),                       // `x` captured by-value into closure
 340     LpDowncast(Rc<LoanPath<'tcx>>, DefId), // `x` downcast to particular enum variant
 341     LpExtend(Rc<LoanPath<'tcx>>, mc::MutabilityCategory, LoanPathElem<'tcx>)
 342 }
 343
 344 impl<'tcx> LoanPath<'tcx> {
 345     fn new(kind: LoanPathKind<'tcx>, ty: Ty<'tcx>) -> LoanPath<'tcx> {
 346         LoanPath { kind: kind, ty: ty }
 347     }
 348
 349     fn to_type(&self) -> Ty<'tcx> { self.ty }
 350
 351     fn has_downcast(&self) -> bool {
 352         match self.kind {
 353             LpDowncast(_, _) => true,
 354             LpExtend(ref lp, _, LpInterior(_, _)) => {
 355                 lp.has_downcast()
 356             }
 357             _ => false,
 358         }
 359     }
 360 }
 361
 362 // FIXME (pnkfelix): See discussion here
 363 // https://github.com/pnkfelix/rust/commit/
 364 //     b2b39e8700e37ad32b486b9a8409b50a8a53aa51#commitcomment-7892003
 365 const DOWNCAST_PRINTED_OPERATOR: &'static str = " as ";
 366
 367 // A local, "cleaned" version of `mc::InteriorKind` that drops
 368 // information that is not relevant to loan-path analysis. (In
 369 // particular, the distinction between how precisely an array-element
 370 // is tracked is irrelevant here.)
 371 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 372 pub enum InteriorKind {
 373     InteriorField(mc::FieldIndex),
 374     InteriorElement,
 375 }
 376
 377 trait ToInteriorKind { fn cleaned(self) -> InteriorKind; }
 378 impl ToInteriorKind for mc::InteriorKind {
 379     fn cleaned(self) -> InteriorKind {
 380         match self {
 381             mc::InteriorField(name) => InteriorField(name),
 382             mc::InteriorElement(_) => InteriorElement,
 383         }
 384     }
 385 }
 386
 387 // This can be:
 388 // - a pointer dereference (`*P` in README.md)
 389 // - a field reference, with an optional definition of the containing
 390 //   enum variant (`P.f` in README.md)
 391 // `DefId` is present when the field is part of struct that is in
 392 // a variant of an enum. For instance in:
 393 // `enum E { X { foo: u32 }, Y { foo: u32 }}`
 394 // each `foo` is qualified by the definitition id of the variant (`X` or `Y`).
 395 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 396 pub enum LoanPathElem<'tcx> {
 397     LpDeref(mc::PointerKind<'tcx>),
 398     LpInterior(Option<DefId>, InteriorKind),
 399 }
 400
 401 fn closure_to_block(closure_id: LocalDefId,
 402                     tcx: TyCtxt<'_, '_, '_>) -> ast::NodeId {
 403     let closure_id = tcx.hir().local_def_id_to_node_id(closure_id);
 404     match tcx.hir().get(closure_id) {
 405         Node::Expr(expr) => match expr.node {
 406             hir::ExprKind::Closure(.., body_id, _, _) => {
 407                 tcx.hir().hir_to_node_id(body_id.hir_id)
 408             }
 409             _ => {
 410                 bug!("encountered non-closure id: {}", closure_id)
 411             }
 412         },
 413         _ => bug!("encountered non-expr id: {}", closure_id)
 414     }
 415 }
 416
 417 impl<'a, 'tcx> LoanPath<'tcx> {
 418     pub fn kill_scope(&self, bccx: &BorrowckCtxt<'a, 'tcx>) -> region::Scope {
 419         match self.kind {
 420             LpVar(local_id) => {
 421                 let hir_id = bccx.tcx.hir().node_to_hir_id(local_id);
 422                 bccx.region_scope_tree.var_scope(hir_id.local_id)
 423             }
 424             LpUpvar(upvar_id) => {
 425                 let block_id = closure_to_block(upvar_id.closure_expr_id, bccx.tcx);
 426                 let hir_id = bccx.tcx.hir().node_to_hir_id(block_id);
 427                 region::Scope { id: hir_id.local_id, data: region::ScopeData::Node }
 428             }
 429             LpDowncast(ref base, _) |
 430             LpExtend(ref base, ..) => base.kill_scope(bccx),
 431         }
 432     }
 433
 434     fn has_fork(&self, other: &LoanPath<'tcx>) -> bool {
 435         match (&self.kind, &other.kind) {
 436             (&LpExtend(ref base, _, LpInterior(opt_variant_id, id)),
 437              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) =>
 438                 if id == id2 && opt_variant_id == opt_variant_id2 {
 439                     base.has_fork(&base2)
 440                 } else {
 441                     true
 442                 },
 443             (&LpExtend(ref base, _, LpDeref(_)), _) => base.has_fork(other),
 444             (_, &LpExtend(ref base, _, LpDeref(_))) => self.has_fork(&base),
 445             _ => false,
 446         }
 447     }
 448
 449     fn depth(&self) -> usize {
 450         match self.kind {
 451             LpExtend(ref base, _, LpDeref(_)) => base.depth(),
 452             LpExtend(ref base, _, LpInterior(..)) => base.depth() + 1,
 453             _ => 0,
 454         }
 455     }
 456
 457     fn common(&self, other: &LoanPath<'tcx>) -> Option<LoanPath<'tcx>> {
 458         match (&self.kind, &other.kind) {
 459             (&LpExtend(ref base, a, LpInterior(opt_variant_id, id)),
 460              &LpExtend(ref base2, _, LpInterior(opt_variant_id2, id2))) => {
 461                 if id == id2 && opt_variant_id == opt_variant_id2 {
 462                     base.common(&base2).map(|x| {
 463                         let xd = x.depth();
 464                         if base.depth() == xd && base2.depth() == xd {
 465                             LoanPath {
 466                                 kind: LpExtend(Rc::new(x), a, LpInterior(opt_variant_id, id)),
 467                                 ty: self.ty,
 468                             }
 469                         } else {
 470                             x
 471                         }
 472                     })
 473                 } else {
 474                     base.common(&base2)
 475                 }
 476             }
 477             (&LpExtend(ref base, _, LpDeref(_)), _) => base.common(other),
 478             (_, &LpExtend(ref other, _, LpDeref(_))) => self.common(&other),
 479             (&LpVar(id), &LpVar(id2)) => {
 480                 if id == id2 {
 481                     Some(LoanPath { kind: LpVar(id), ty: self.ty })
 482                 } else {
 483                     None
 484                 }
 485             }
 486             (&LpUpvar(id), &LpUpvar(id2)) => {
 487                 if id == id2 {
 488                     Some(LoanPath { kind: LpUpvar(id), ty: self.ty })
 489                 } else {
 490                     None
 491                 }
 492             }
 493             _ => None,
 494         }
 495     }
 496 }
 497
 498 // Avoid "cannot borrow immutable field `self.x` as mutable" as that implies that a field *can* be
 499 // mutable independently of the struct it belongs to. (#35937)
 500 pub fn opt_loan_path_is_field<'tcx>(cmt: &mc::cmt_<'tcx>) -> (Option<Rc<LoanPath<'tcx>>>, bool) {
 501     let new_lp = |v: LoanPathKind<'tcx>| Rc::new(LoanPath::new(v, cmt.ty));
 502
 503     match cmt.cat {
 504         Categorization::Rvalue(..) |
 505         Categorization::ThreadLocal(..) |
 506         Categorization::StaticItem => {
 507             (None, false)
 508         }
 509
 510         Categorization::Local(id) => {
 511             (Some(new_lp(LpVar(id))), false)
 512         }
 513
 514         Categorization::Upvar(mc::Upvar { id, .. }) => {
 515             (Some(new_lp(LpUpvar(id))), false)
 516         }
 517
 518         Categorization::Deref(ref cmt_base, pk) => {
 519             let lp = opt_loan_path_is_field(cmt_base);
 520             (lp.0.map(|lp| {
 521                 new_lp(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
 522             }), lp.1)
 523         }
 524
 525         Categorization::Interior(ref cmt_base, ik) => {
 526             (opt_loan_path(cmt_base).map(|lp| {
 527                 let opt_variant_id = match cmt_base.cat {
 528                     Categorization::Downcast(_, did) =>  Some(did),
 529                     _ => None
 530                 };
 531                 new_lp(LpExtend(lp, cmt.mutbl, LpInterior(opt_variant_id, ik.cleaned())))
 532             }), true)
 533         }
 534
 535         Categorization::Downcast(ref cmt_base, variant_def_id) => {
 536             let lp = opt_loan_path_is_field(cmt_base);
 537             (lp.0.map(|lp| {
 538                 new_lp(LpDowncast(lp, variant_def_id))
 539             }), lp.1)
 540         }
 541     }
 542 }
 543
 544 /// Computes the `LoanPath` (if any) for a `cmt`.
 545 /// Note that this logic is somewhat duplicated in
 546 /// the method `compute()` found in `gather_loans::restrictions`,
 547 /// which allows it to share common loan path pieces as it
 548 /// traverses the CMT.
 549 pub fn opt_loan_path<'tcx>(cmt: &mc::cmt_<'tcx>) -> Option<Rc<LoanPath<'tcx>>> {
 550     opt_loan_path_is_field(cmt).0
 551 }
 552
 553 ///////////////////////////////////////////////////////////////////////////
 554 // Errors
 555
 556 // Errors that can occur
 557 #[derive(Debug, PartialEq)]
 558 pub enum bckerr_code<'tcx> {
 559     err_mutbl,
 560     /// superscope, subscope, loan cause
 561     err_out_of_scope(ty::Region<'tcx>, ty::Region<'tcx>, euv::LoanCause),
 562     err_borrowed_pointer_too_short(ty::Region<'tcx>, ty::Region<'tcx>), // loan, ptr
 563 }
 564
 565 // Combination of an error code and the categorization of the expression
 566 // that caused it
 567 #[derive(Debug, PartialEq)]
 568 pub struct BckError<'c, 'tcx: 'c> {
 569     span: Span,
 570     cause: AliasableViolationKind,
 571     cmt: &'c mc::cmt_<'tcx>,
 572     code: bckerr_code<'tcx>
 573 }
 574
 575 #[derive(Copy, Clone, Debug, PartialEq)]
 576 pub enum AliasableViolationKind {
 577     MutabilityViolation,
 578     BorrowViolation(euv::LoanCause)
 579 }
 580
 581 #[derive(Copy, Clone, Debug)]
 582 pub enum MovedValueUseKind {
 583     MovedInUse,
 584     MovedInCapture,
 585 }
 586
 587 ///////////////////////////////////////////////////////////////////////////
 588 // Misc
 589
 590 impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
 591     pub fn is_subregion_of(&self,
 592                            r_sub: ty::Region<'tcx>,
 593                            r_sup: ty::Region<'tcx>)
 594                            -> bool
 595     {
 596         let region_rels = RegionRelations::new(self.tcx,
 597                                                self.owner_def_id,
 598                                                &self.region_scope_tree,
 599                                                &self.tables.free_region_map);
 600         region_rels.is_subregion_of(r_sub, r_sup)
 601     }
 602
 603     pub fn report(&self, err: BckError<'a, 'tcx>) {
 604         // Catch and handle some particular cases.
 605         match (&err.code, &err.cause) {
 606             (&err_out_of_scope(&ty::ReScope(_), &ty::ReStatic, _),
 607              &BorrowViolation(euv::ClosureCapture(span))) |
 608             (&err_out_of_scope(&ty::ReScope(_), &ty::ReEarlyBound(..), _),
 609              &BorrowViolation(euv::ClosureCapture(span))) |
 610             (&err_out_of_scope(&ty::ReScope(_), &ty::ReFree(..), _),
 611              &BorrowViolation(euv::ClosureCapture(span))) => {
 612                 return self.report_out_of_scope_escaping_closure_capture(&err, span);
 613             }
 614             _ => { }
 615         }
 616
 617         self.report_bckerr(&err);
 618     }
 619
 620     pub fn report_use_of_moved_value(&self,
 621                                      use_span: Span,
 622                                      use_kind: MovedValueUseKind,
 623                                      lp: &LoanPath<'tcx>,
 624                                      the_move: &move_data::Move,
 625                                      moved_lp: &LoanPath<'tcx>) {
 626         let (verb, verb_participle) = match use_kind {
 627             MovedInUse => ("use", "used"),
 628             MovedInCapture => ("capture", "captured"),
 629         };
 630
 631         let (_ol, _moved_lp_msg, mut err, need_note) = match the_move.kind {
 632             move_data::Declared => {
 633                 // If this is an uninitialized variable, just emit a simple warning
 634                 // and return.
 635                 self.cannot_act_on_uninitialized_variable(use_span,
 636                                                           verb,
 637                                                           &self.loan_path_to_string(lp),
 638                                                           Origin::Ast)
 639                     .span_label(use_span, format!("use of possibly uninitialized `{}`",
 640                                                   self.loan_path_to_string(lp)))
 641                     .emit();
 642                 self.signal_error();
 643                 return;
 644             }
 645             _ => {
 646                 // If moved_lp is something like `x.a`, and lp is something like `x.b`, we would
 647                 // normally generate a rather confusing message:
 648                 //
 649                 //     error: use of moved value: `x.b`
 650                 //     note: `x.a` moved here...
 651                 //
 652                 // What we want to do instead is get the 'common ancestor' of the two moves and
 653                 // use that for most of the message instead, giving is something like this:
 654                 //
 655                 //     error: use of moved value: `x`
 656                 //     note: `x` moved here (through moving `x.a`)...
 657
 658                 let common = moved_lp.common(lp);
 659                 let has_common = common.is_some();
 660                 let has_fork = moved_lp.has_fork(lp);
 661                 let (nl, ol, moved_lp_msg) =
 662                     if has_fork && has_common {
 663                         let nl = self.loan_path_to_string(&common.unwrap());
 664                         let ol = nl.clone();
 665                         let moved_lp_msg = format!(" (through moving `{}`)",
 666                                                    self.loan_path_to_string(moved_lp));
 667                         (nl, ol, moved_lp_msg)
 668                     } else {
 669                         (self.loan_path_to_string(lp),
 670                          self.loan_path_to_string(moved_lp),
 671                          String::new())
 672                     };
 673
 674                 let partial = moved_lp.depth() > lp.depth();
 675                 let msg = if !has_fork && partial { "partially " }
 676                           else if has_fork && !has_common { "collaterally "}
 677                 else { "" };
 678                 let mut err = self.cannot_act_on_moved_value(use_span,
 679                                                              verb,
 680                                                              msg,
 681                                                              Some(nl),
 682                                                              Origin::Ast);
 683                 let need_note = match lp.ty.sty {
 684                     ty::Closure(id, _) => {
 685                         let node_id = self.tcx.hir().as_local_node_id(id).unwrap();
 686                         let hir_id = self.tcx.hir().node_to_hir_id(node_id);
 687                         if let Some((span, name)) = self.tables.closure_kind_origins().get(hir_id) {
 688                             err.span_note(*span, &format!(
 689                                 "closure cannot be invoked more than once because \
 690                                 it moves the variable `{}` out of its environment",
 691                                 name
 692                             ));
 693                             false
 694                         } else {
 695                             true
 696                         }
 697                     }
 698                     _ => true,
 699                 };
 700                 (ol, moved_lp_msg, err, need_note)
 701             }
 702         };
 703
 704         // Get type of value and span where it was previously
 705         // moved.
 706         let node_id = self.tcx.hir().hir_to_node_id(hir::HirId {
 707             owner: self.body.value.hir_id.owner,
 708             local_id: the_move.id
 709         });
 710         let (move_span, move_note) = match the_move.kind {
 711             move_data::Declared => {
 712                 unreachable!();
 713             }
 714
 715             move_data::MoveExpr |
 716             move_data::MovePat => (self.tcx.hir().span(node_id), ""),
 717
 718             move_data::Captured =>
 719                 (match self.tcx.hir().expect_expr(node_id).node {
 720                     hir::ExprKind::Closure(.., fn_decl_span, _) => fn_decl_span,
 721                     ref r => bug!("Captured({:?}) maps to non-closure: {:?}",
 722                                   the_move.id, r),
 723                 }, " (into closure)"),
 724         };
 725
 726         // Annotate the use and the move in the span. Watch out for
 727         // the case where the use and the move are the same. This
 728         // means the use is in a loop.
 729         err = if use_span == move_span {
 730             err.span_label(
 731                 use_span,
 732                 format!("value moved{} here in previous iteration of loop",
 733                          move_note));
 734             err
 735         } else {
 736             err.span_label(use_span, format!("value {} here after move", verb_participle));
 737             err.span_label(move_span, format!("value moved{} here", move_note));
 738             err
 739         };
 740
 741         if need_note {
 742             err.note(&format!(
 743                 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 744                 if moved_lp.has_downcast() {
 745                     "the value".to_string()
 746                 } else {
 747                     format!("`{}`", self.loan_path_to_string(moved_lp))
 748                 },
 749                 moved_lp.ty));
 750         }
 751
 752         // Note: we used to suggest adding a `ref binding` or calling
 753         // `clone` but those suggestions have been removed because
 754         // they are often not what you actually want to do, and were
 755         // not considered particularly helpful.
 756
 757         err.emit();
 758         self.signal_error();
 759     }
 760
 761     pub fn report_partial_reinitialization_of_uninitialized_structure(
 762             &self,
 763             span: Span,
 764             lp: &LoanPath<'tcx>) {
 765         self.cannot_partially_reinit_an_uninit_struct(span,
 766                                                       &self.loan_path_to_string(lp),
 767                                                       Origin::Ast)
 768             .emit();
 769         self.signal_error();
 770     }
 771
 772     pub fn report_reassigned_immutable_variable(&self,
 773                                                 span: Span,
 774                                                 lp: &LoanPath<'tcx>,
 775                                                 assign:
 776                                                 &move_data::Assignment) {
 777         let mut err = self.cannot_reassign_immutable(span,
 778                                                      &self.loan_path_to_string(lp),
 779                                                      false,
 780                                                      Origin::Ast);
 781         err.span_label(span, "cannot assign twice to immutable variable");
 782         if span != assign.span {
 783             err.span_label(assign.span, format!("first assignment to `{}`",
 784                                                 self.loan_path_to_string(lp)));
 785         }
 786         err.emit();
 787         self.signal_error();
 788     }
 789
 790     fn report_bckerr(&self, err: &BckError<'a, 'tcx>) {
 791         let error_span = err.span.clone();
 792
 793         match err.code {
 794             err_mutbl => {
 795                 let descr: Cow<'static, str> = match err.cmt.note {
 796                     mc::NoteClosureEnv(_) | mc::NoteUpvarRef(_) => {
 797                         self.cmt_to_cow_str(&err.cmt)
 798                     }
 799                     _ => match opt_loan_path_is_field(&err.cmt) {
 800                         (None, true) => {
 801                             format!("{} of {} binding",
 802                                     self.cmt_to_cow_str(&err.cmt),
 803                                     err.cmt.mutbl.to_user_str()).into()
 804
 805                         }
 806                         (None, false) => {
 807                             format!("{} {}",
 808                                     err.cmt.mutbl.to_user_str(),
 809                                     self.cmt_to_cow_str(&err.cmt)).into()
 810
 811                         }
 812                         (Some(lp), true) => {
 813                             format!("{} `{}` of {} binding",
 814                                     self.cmt_to_cow_str(&err.cmt),
 815                                     self.loan_path_to_string(&lp),
 816                                     err.cmt.mutbl.to_user_str()).into()
 817                         }
 818                         (Some(lp), false) => {
 819                             format!("{} {} `{}`",
 820                                     err.cmt.mutbl.to_user_str(),
 821                                     self.cmt_to_cow_str(&err.cmt),
 822                                     self.loan_path_to_string(&lp)).into()
 823                         }
 824                     }
 825                 };
 826
 827                 let mut db = match err.cause {
 828                     MutabilityViolation => {
 829                         let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
 830                         if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
 831                             let node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
 832                             let sp = self.tcx.hir().span(node_id);
 833                             let fn_closure_msg = "`Fn` closures cannot capture their enclosing \
 834                                                   environment for modifications";
 835                             match (self.tcx.sess.source_map().span_to_snippet(sp), &err.cmt.cat) {
 836                                 (_, &Categorization::Upvar(mc::Upvar {
 837                                     kind: ty::ClosureKind::Fn, ..
 838                                 })) => {
 839                                     db.note(fn_closure_msg);
 840                                     // we should point at the cause for this closure being
 841                                     // identified as `Fn` (like in signature of method this
 842                                     // closure was passed into)
 843                                 }
 844                                 (Ok(ref snippet), ref cat) => {
 845                                     let msg = &format!("consider making `{}` mutable", snippet);
 846                                     let suggestion = format!("mut {}", snippet);
 847
 848                                     if let &Categorization::Deref(ref cmt, _) = cat {
 849                                         if let Categorization::Upvar(mc::Upvar {
 850                                             kind: ty::ClosureKind::Fn, ..
 851                                         }) = cmt.cat {
 852                                             db.note(fn_closure_msg);
 853                                         } else {
 854                                             db.span_suggestion(
 855                                                 sp,
 856                                                 msg,
 857                                                 suggestion,
 858                                                 Applicability::Unspecified,
 859                                             );
 860                                         }
 861                                     } else {
 862                                         db.span_suggestion(
 863                                             sp,
 864                                             msg,
 865                                             suggestion,
 866                                             Applicability::Unspecified,
 867                                         );
 868                                     }
 869                                 }
 870                                 _ => {
 871                                     db.span_help(sp, "consider making this binding mutable");
 872                                 }
 873                             }
 874                         }
 875
 876                         db
 877                     }
 878                     BorrowViolation(euv::ClosureCapture(_)) => {
 879                         self.closure_cannot_assign_to_borrowed(error_span, &descr, Origin::Ast)
 880                     }
 881                     BorrowViolation(euv::OverloadedOperator) |
 882                     BorrowViolation(euv::AddrOf) |
 883                     BorrowViolation(euv::RefBinding) |
 884                     BorrowViolation(euv::AutoRef) |
 885                     BorrowViolation(euv::AutoUnsafe) |
 886                     BorrowViolation(euv::ForLoop) |
 887                     BorrowViolation(euv::MatchDiscriminant) => {
 888                         self.cannot_borrow_path_as_mutable(error_span, &descr, Origin::Ast)
 889                     }
 890                     BorrowViolation(euv::ClosureInvocation) => {
 891                         span_bug!(err.span,
 892                             "err_mutbl with a closure invocation");
 893                     }
 894                 };
 895
 896                 // We add a special note about `IndexMut`, if the source of this error
 897                 // is the fact that `Index` is implemented, but `IndexMut` is not. Needing
 898                 // to implement two traits for "one operator" is not very intuitive for
 899                 // many programmers.
 900                 if err.cmt.note == mc::NoteIndex {
 901                     let node_id = self.tcx.hir().hir_to_node_id(err.cmt.hir_id);
 902                     let node =  self.tcx.hir().get(node_id);
 903
 904                     // This pattern probably always matches.
 905                     if let Node::Expr(
 906                         hir::Expr { node: hir::ExprKind::Index(lhs, _), ..}
 907                     ) = node {
 908                         let ty = self.tables.expr_ty(lhs);
 909
 910                         db.help(&format!(
 911                             "trait `IndexMut` is required to modify indexed content, but \
 912                              it is not implemented for `{}`",
 913                             ty
 914                         ));
 915                     }
 916                 }
 917
 918                 self.note_and_explain_mutbl_error(&mut db, &err, &error_span);
 919                 self.note_immutability_blame(
 920                     &mut db,
 921                     err.cmt.immutability_blame(),
 922                     self.tcx.hir().hir_to_node_id(err.cmt.hir_id)
 923                 );
 924                 db.emit();
 925                 self.signal_error();
 926             }
 927             err_out_of_scope(super_scope, sub_scope, cause) => {
 928                 let msg = match opt_loan_path(&err.cmt) {
 929                     None => "borrowed value".to_string(),
 930                     Some(lp) => {
 931                         format!("`{}`", self.loan_path_to_string(&lp))
 932                     }
 933                 };
 934
 935                 let mut db = self.path_does_not_live_long_enough(error_span, &msg, Origin::Ast);
 936                 let value_kind = match err.cmt.cat {
 937                     mc::Categorization::Rvalue(..) => "temporary value",
 938                     _ => "borrowed value",
 939                 };
 940
 941                 let is_closure = match cause {
 942                     euv::ClosureCapture(s) => {
 943                         // The primary span starts out as the closure creation point.
 944                         // Change the primary span here to highlight the use of the variable
 945                         // in the closure, because it seems more natural. Highlight
 946                         // closure creation point as a secondary span.
 947                         match db.span.primary_span() {
 948                             Some(primary) => {
 949                                 db.span = MultiSpan::from_span(s);
 950                                 db.span_label(primary, "capture occurs here");
 951                                 db.span_label(s, format!("{} does not live long enough",
 952                                                          value_kind));
 953                                 true
 954                             }
 955                             None => false
 956                         }
 957                     }
 958                     _ => {
 959                         db.span_label(error_span, format!("{} does not live long enough",
 960                                                           value_kind));
 961                         false
 962                     }
 963                 };
 964
 965                 let sub_span = self.region_end_span(sub_scope);
 966                 let super_span = self.region_end_span(super_scope);
 967
 968                 match (sub_span, super_span) {
 969                     (Some(s1), Some(s2)) if s1 == s2 => {
 970                         if !is_closure {
 971                             let msg = match opt_loan_path(&err.cmt) {
 972                                 None => value_kind.to_string(),
 973                                 Some(lp) => {
 974                                     format!("`{}`", self.loan_path_to_string(&lp))
 975                                 }
 976                             };
 977                             db.span_label(s1,
 978                                           format!("{} dropped here while still borrowed", msg));
 979                         } else {
 980                             db.span_label(s1, format!("{} dropped before borrower", value_kind));
 981                         }
 982                         db.note("values in a scope are dropped in the opposite order \
 983                                 they are created");
 984                     }
 985                     (Some(s1), Some(s2)) if !is_closure => {
 986                         let msg = match opt_loan_path(&err.cmt) {
 987                             None => value_kind.to_string(),
 988                             Some(lp) => {
 989                                 format!("`{}`", self.loan_path_to_string(&lp))
 990                             }
 991                         };
 992                         db.span_label(s2, format!("{} dropped here while still borrowed", msg));
 993                         db.span_label(s1, format!("{} needs to live until here", value_kind));
 994                     }
 995                     _ => {
 996                         match sub_span {
 997                             Some(s) => {
 998                                 db.span_label(s, format!("{} needs to live until here",
 999                                                           value_kind));
1000                             }
1001                             None => {
1002                                 self.tcx.note_and_explain_region(
1003                                     &self.region_scope_tree,
1004                                     &mut db,
1005                                     "borrowed value must be valid for ",
1006                                     sub_scope,
1007                                     "...");
1008                             }
1009                         }
1010                         match super_span {
1011                             Some(s) => {
1012                                 db.span_label(s, format!("{} only lives until here", value_kind));
1013                             }
1014                             None => {
1015                                 self.tcx.note_and_explain_region(
1016                                     &self.region_scope_tree,
1017                                     &mut db,
1018                                     "...but borrowed value is only valid for ",
1019                                     super_scope,
1020                                     "");
1021                             }
1022                         }
1023                     }
1024                 }
1025
1026                 if let ty::ReScope(scope) = *super_scope {
1027                     let node_id = scope.node_id(self.tcx, &self.region_scope_tree);
1028                     match self.tcx.hir().find(node_id) {
1029                         Some(Node::Stmt(_)) => {
1030                             if *sub_scope != ty::ReStatic {
1031                                 db.note("consider using a `let` binding to increase its lifetime");
1032                             }
1033
1034                         }
1035                         _ => {}
1036                     }
1037                 }
1038
1039                 db.emit();
1040                 self.signal_error();
1041             }
1042             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {
1043                 let descr = self.cmt_to_path_or_string(err.cmt);
1044                 let mut db = self.lifetime_too_short_for_reborrow(error_span, &descr, Origin::Ast);
1045                 let descr: Cow<'static, str> = match opt_loan_path(&err.cmt) {
1046                     Some(lp) => {
1047                         format!("`{}`", self.loan_path_to_string(&lp)).into()
1048                     }
1049                     None => self.cmt_to_cow_str(&err.cmt)
1050                 };
1051                 self.tcx.note_and_explain_region(
1052                     &self.region_scope_tree,
1053                     &mut db,
1054                     &format!("{} would have to be valid for ",
1055                             descr),
1056                     loan_scope,
1057                     "...");
1058                 self.tcx.note_and_explain_region(
1059                     &self.region_scope_tree,
1060                     &mut db,
1061                     &format!("...but {} is only valid for ", descr),
1062                     ptr_scope,
1063                     "");
1064
1065                 db.emit();
1066                 self.signal_error();
1067             }
1068         }
1069     }
1070
1071     pub fn report_aliasability_violation(&self,
1072                                          span: Span,
1073                                          kind: AliasableViolationKind,
1074                                          cause: mc::AliasableReason,
1075                                          cmt: &mc::cmt_<'tcx>) {
1076         let mut is_closure = false;
1077         let prefix = match kind {
1078             MutabilityViolation => {
1079                 "cannot assign to data"
1080             }
1081             BorrowViolation(euv::ClosureCapture(_)) |
1082             BorrowViolation(euv::OverloadedOperator) |
1083             BorrowViolation(euv::AddrOf) |
1084             BorrowViolation(euv::AutoRef) |
1085             BorrowViolation(euv::AutoUnsafe) |
1086             BorrowViolation(euv::RefBinding) |
1087             BorrowViolation(euv::MatchDiscriminant) => {
1088                 "cannot borrow data mutably"
1089             }
1090
1091             BorrowViolation(euv::ClosureInvocation) => {
1092                 is_closure = true;
1093                 "closure invocation"
1094             }
1095
1096             BorrowViolation(euv::ForLoop) => {
1097                 "`for` loop"
1098             }
1099         };
1100
1101         match cause {
1102             mc::AliasableStaticMut => {
1103                 // This path cannot occur. `static mut X` is not checked
1104                 // for aliasability violations.
1105                 span_bug!(span, "aliasability violation for static mut `{}`", prefix)
1106             }
1107             mc::AliasableStatic | mc::AliasableBorrowed => {}
1108         };
1109         let blame = cmt.immutability_blame();
1110         let mut err = match blame {
1111             Some(ImmutabilityBlame::ClosureEnv(id)) => {
1112                 // FIXME: the distinction between these 2 messages looks wrong.
1113                 let help_msg = if let BorrowViolation(euv::ClosureCapture(_)) = kind {
1114                     // The aliasability violation with closure captures can
1115                     // happen for nested closures, so we know the enclosing
1116                     // closure incorrectly accepts an `Fn` while it needs to
1117                     // be `FnMut`.
1118                     "consider changing this to accept closures that implement `FnMut`"
1119
1120                 } else {
1121                     "consider changing this closure to take self by mutable reference"
1122                 };
1123                 let node_id = self.tcx.hir().local_def_id_to_node_id(id);
1124                 let help_span = self.tcx.hir().span(node_id);
1125                 self.cannot_act_on_capture_in_sharable_fn(span,
1126                                                           prefix,
1127                                                           (help_span, help_msg),
1128                                                           Origin::Ast)
1129             }
1130             _ =>  {
1131                 self.cannot_assign_into_immutable_reference(span, prefix,
1132                                                             Origin::Ast)
1133             }
1134         };
1135         self.note_immutability_blame(
1136             &mut err,
1137             blame,
1138             self.tcx.hir().hir_to_node_id(cmt.hir_id)
1139         );
1140
1141         if is_closure {
1142             err.help("closures behind references must be called via `&mut`");
1143         }
1144         err.emit();
1145         self.signal_error();
1146     }
1147
1148     /// Given a type, if it is an immutable reference, return a suggestion to make it mutable
1149     fn suggest_mut_for_immutable(&self, pty: &hir::Ty, is_implicit_self: bool) -> Option<String> {
1150         // Check whether the argument is an immutable reference
1151         debug!("suggest_mut_for_immutable({:?}, {:?})", pty, is_implicit_self);
1152         if let hir::TyKind::Rptr(lifetime, hir::MutTy {
1153             mutbl: hir::Mutability::MutImmutable,
1154             ref ty
1155         }) = pty.node {
1156             // Account for existing lifetimes when generating the message
1157             let pointee_snippet = match self.tcx.sess.source_map().span_to_snippet(ty.span) {
1158                 Ok(snippet) => snippet,
1159                 _ => return None
1160             };
1161
1162             let lifetime_snippet = if !lifetime.is_elided() {
1163                 format!("{} ", match self.tcx.sess.source_map().span_to_snippet(lifetime.span) {
1164                     Ok(lifetime_snippet) => lifetime_snippet,
1165                     _ => return None
1166                 })
1167             } else {
1168                 String::new()
1169             };
1170             Some(format!("use `&{}mut {}` here to make mutable",
1171                          lifetime_snippet,
1172                          if is_implicit_self { "self" } else { &*pointee_snippet }))
1173         } else {
1174             None
1175         }
1176     }
1177
1178     fn local_binding_mode(&self, node_id: ast::NodeId) -> ty::BindingMode {
1179         let pat = match self.tcx.hir().get(node_id) {
1180             Node::Binding(pat) => pat,
1181             node => bug!("bad node for local: {:?}", node)
1182         };
1183
1184         match pat.node {
1185             hir::PatKind::Binding(..) => {
1186                 *self.tables
1187                      .pat_binding_modes()
1188                      .get(pat.hir_id)
1189                      .expect("missing binding mode")
1190             }
1191             _ => bug!("local is not a binding: {:?}", pat)
1192         }
1193     }
1194
1195     fn local_ty(&self, node_id: ast::NodeId) -> (Option<&hir::Ty>, bool) {
1196         let parent = self.tcx.hir().get_parent_node(node_id);
1197         let parent_node = self.tcx.hir().get(parent);
1198
1199         // The parent node is like a fn
1200         if let Some(fn_like) = FnLikeNode::from_node(parent_node) {
1201             // `nid`'s parent's `Body`
1202             let fn_body = self.tcx.hir().body(fn_like.body());
1203             // Get the position of `node_id` in the arguments list
1204             let arg_pos = fn_body.arguments.iter().position(|arg| arg.pat.id == node_id);
1205             if let Some(i) = arg_pos {
1206                 // The argument's `Ty`
1207                 (Some(&fn_like.decl().inputs[i]),
1208                  i == 0 && fn_like.decl().implicit_self.has_implicit_self())
1209             } else {
1210                 (None, false)
1211             }
1212         } else {
1213             (None, false)
1214         }
1215     }
1216
1217     fn note_immutability_blame(&self,
1218                                db: &mut DiagnosticBuilder<'_>,
1219                                blame: Option<ImmutabilityBlame<'_>>,
1220                                error_node_id: ast::NodeId) {
1221         match blame {
1222             None => {}
1223             Some(ImmutabilityBlame::ClosureEnv(_)) => {}
1224             Some(ImmutabilityBlame::ImmLocal(node_id)) => {
1225                 self.note_immutable_local(db, error_node_id, node_id)
1226             }
1227             Some(ImmutabilityBlame::LocalDeref(node_id)) => {
1228                 match self.local_binding_mode(node_id) {
1229                     ty::BindByReference(..) => {
1230                         let let_span = self.tcx.hir().span(node_id);
1231                         let suggestion = suggest_ref_mut(self.tcx, let_span);
1232                         if let Some(replace_str) = suggestion {
1233                             db.span_suggestion(
1234                                 let_span,
1235                                 "use a mutable reference instead",
1236                                 replace_str,
1237                                 // I believe this can be machine applicable,
1238                                 // but if there are multiple attempted uses of an immutable
1239                                 // reference, I don't know how rustfix handles it, it might
1240                                 // attempt fixing them multiple times.
1241                                 //                              @estebank
1242                                 Applicability::Unspecified,
1243                             );
1244                         }
1245                     }
1246                     ty::BindByValue(..) => {
1247                         if let (Some(local_ty), is_implicit_self) = self.local_ty(node_id) {
1248                             if let Some(msg) =
1249                                  self.suggest_mut_for_immutable(local_ty, is_implicit_self) {
1250                                 db.span_label(local_ty.span, msg);
1251                             }
1252                         }
1253                     }
1254                 }
1255             }
1256             Some(ImmutabilityBlame::AdtFieldDeref(_, field)) => {
1257                 let node_id = match self.tcx.hir().as_local_node_id(field.did) {
1258                     Some(node_id) => node_id,
1259                     None => return
1260                 };
1261
1262                 if let Node::Field(ref field) = self.tcx.hir().get(node_id) {
1263                     if let Some(msg) = self.suggest_mut_for_immutable(&field.ty, false) {
1264                         db.span_label(field.ty.span, msg);
1265                     }
1266                 }
1267             }
1268         }
1269     }
1270
1271      // Suggest a fix when trying to mutably borrow an immutable local
1272      // binding: either to make the binding mutable (if its type is
1273      // not a mutable reference) or to avoid borrowing altogether
1274     fn note_immutable_local(&self,
1275                             db: &mut DiagnosticBuilder<'_>,
1276                             borrowed_node_id: ast::NodeId,
1277                             binding_node_id: ast::NodeId) {
1278         let let_span = self.tcx.hir().span(binding_node_id);
1279         if let ty::BindByValue(..) = self.local_binding_mode(binding_node_id) {
1280             if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(let_span) {
1281                 let (ty, is_implicit_self) = self.local_ty(binding_node_id);
1282                 if is_implicit_self && snippet != "self" {
1283                     // avoid suggesting `mut &self`.
1284                     return
1285                 }
1286                 if let Some(&hir::TyKind::Rptr(
1287                     _,
1288                     hir::MutTy {
1289                         mutbl: hir::MutMutable,
1290                         ..
1291                     },
1292                 )) = ty.map(|t| &t.node)
1293                 {
1294                     let borrow_expr_id = self.tcx.hir().get_parent_node(borrowed_node_id);
1295                     db.span_suggestion(
1296                         self.tcx.hir().span(borrow_expr_id),
1297                         "consider removing the `&mut`, as it is an \
1298                         immutable binding to a mutable reference",
1299                         snippet,
1300                         Applicability::MachineApplicable,
1301                     );
1302                 } else {
1303                     db.span_suggestion(
1304                         let_span,
1305                         "make this binding mutable",
1306                         format!("mut {}", snippet),
1307                         Applicability::MachineApplicable,
1308                     );
1309                 }
1310             }
1311         }
1312     }
1313
1314     fn report_out_of_scope_escaping_closure_capture(&self,
1315                                                     err: &BckError<'a, 'tcx>,
1316                                                     capture_span: Span)
1317     {
1318         let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
1319
1320         let suggestion =
1321             match self.tcx.sess.source_map().span_to_snippet(err.span) {
1322                 Ok(string) => format!("move {}", string),
1323                 Err(_) => "move |<args>| <body>".to_string()
1324             };
1325
1326         self.cannot_capture_in_long_lived_closure(err.span,
1327                                                   &cmt_path_or_string,
1328                                                   capture_span,
1329                                                   Origin::Ast)
1330             .span_suggestion(
1331                  err.span,
1332                  &format!("to force the closure to take ownership of {} \
1333                            (and any other referenced variables), \
1334                            use the `move` keyword",
1335                            cmt_path_or_string),
1336                  suggestion,
1337                  Applicability::MachineApplicable,
1338             )
1339             .emit();
1340         self.signal_error();
1341     }
1342
1343     fn region_end_span(&self, region: ty::Region<'tcx>) -> Option<Span> {
1344         match *region {
1345             ty::ReScope(scope) => {
1346                 Some(self.tcx.sess.source_map().end_point(
1347                         scope.span(self.tcx, &self.region_scope_tree)))
1348             }
1349             _ => None
1350         }
1351     }
1352
1353     fn note_and_explain_mutbl_error(&self, db: &mut DiagnosticBuilder<'_>, err: &BckError<'a, 'tcx>,
1354                                     error_span: &Span) {
1355         match err.cmt.note {
1356             mc::NoteClosureEnv(upvar_id) | mc::NoteUpvarRef(upvar_id) => {
1357                 // If this is an `Fn` closure, it simply can't mutate upvars.
1358                 // If it's an `FnMut` closure, the original variable was declared immutable.
1359                 // We need to determine which is the case here.
1360                 let kind = match err.cmt.upvar_cat().unwrap() {
1361                     Categorization::Upvar(mc::Upvar { kind, .. }) => kind,
1362                     _ => bug!()
1363                 };
1364                 if *kind == ty::ClosureKind::Fn {
1365                     let closure_node_id =
1366                         self.tcx.hir().local_def_id_to_node_id(upvar_id.closure_expr_id);
1367                     db.span_help(self.tcx.hir().span(closure_node_id),
1368                                  "consider changing this closure to take \
1369                                   self by mutable reference");
1370                 }
1371             }
1372             _ => {
1373                 if let Categorization::Deref(..) = err.cmt.cat {
1374                     db.span_label(*error_span, "cannot borrow as mutable");
1375                 } else if let Categorization::Local(local_id) = err.cmt.cat {
1376                     let span = self.tcx.hir().span(local_id);
1377                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1378                         if snippet.starts_with("ref mut ") || snippet.starts_with("&mut ") {
1379                             db.span_label(*error_span, "cannot reborrow mutably");
1380                             db.span_label(*error_span, "try removing `&mut` here");
1381                         } else {
1382                             db.span_label(*error_span, "cannot borrow mutably");
1383                         }
1384                     } else {
1385                         db.span_label(*error_span, "cannot borrow mutably");
1386                     }
1387                 } else if let Categorization::Interior(ref cmt, _) = err.cmt.cat {
1388                     if let mc::MutabilityCategory::McImmutable = cmt.mutbl {
1389                         db.span_label(*error_span,
1390                                       "cannot mutably borrow field of immutable binding");
1391                     }
1392                 }
1393             }
1394         }
1395     }
1396     pub fn append_loan_path_to_string(&self,
1397                                       loan_path: &LoanPath<'tcx>,
1398                                       out: &mut String) {
1399         match loan_path.kind {
1400             LpUpvar(ty::UpvarId { var_path: ty::UpvarPath { hir_id: id}, closure_expr_id: _ }) => {
1401                 out.push_str(&self.tcx.hir().name(self.tcx.hir().hir_to_node_id(id)).as_str());
1402             }
1403             LpVar(id) => {
1404                 out.push_str(&self.tcx.hir().name(id).as_str());
1405             }
1406
1407             LpDowncast(ref lp_base, variant_def_id) => {
1408                 out.push('(');
1409                 self.append_loan_path_to_string(&lp_base, out);
1410                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1411                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1412                 out.push(')');
1413             }
1414
1415             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(mc::FieldIndex(_, info)))) => {
1416                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1417                 out.push('.');
1418                 out.push_str(&info.as_str());
1419             }
1420
1421             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) => {
1422                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1423                 out.push_str("[..]");
1424             }
1425
1426             LpExtend(ref lp_base, _, LpDeref(_)) => {
1427                 out.push('*');
1428                 self.append_loan_path_to_string(&lp_base, out);
1429             }
1430         }
1431     }
1432
1433     pub fn append_autoderefd_loan_path_to_string(&self,
1434                                                  loan_path: &LoanPath<'tcx>,
1435                                                  out: &mut String) {
1436         match loan_path.kind {
1437             LpExtend(ref lp_base, _, LpDeref(_)) => {
1438                 // For a path like `(*x).f` or `(*x)[3]`, autoderef
1439                 // rules would normally allow users to omit the `*x`.
1440                 // So just serialize such paths to `x.f` or x[3]` respectively.
1441                 self.append_autoderefd_loan_path_to_string(&lp_base, out)
1442             }
1443
1444             LpDowncast(ref lp_base, variant_def_id) => {
1445                 out.push('(');
1446                 self.append_autoderefd_loan_path_to_string(&lp_base, out);
1447                 out.push_str(DOWNCAST_PRINTED_OPERATOR);
1448                 out.push_str(&self.tcx.item_path_str(variant_def_id));
1449                 out.push(')');
1450             }
1451
1452             LpVar(..) | LpUpvar(..) | LpExtend(.., LpInterior(..)) => {
1453                 self.append_loan_path_to_string(loan_path, out)
1454             }
1455         }
1456     }
1457
1458     pub fn loan_path_to_string(&self, loan_path: &LoanPath<'tcx>) -> String {
1459         let mut result = String::new();
1460         self.append_loan_path_to_string(loan_path, &mut result);
1461         result
1462     }
1463
1464     pub fn cmt_to_cow_str(&self, cmt: &mc::cmt_<'tcx>) -> Cow<'static, str> {
1465         cmt.descriptive_string(self.tcx)
1466     }
1467
1468     pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
1469         match opt_loan_path(cmt) {
1470             Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
1471             None => self.cmt_to_cow_str(cmt).into_owned(),
1472         }
1473     }
1474 }
1475
1476 impl BitwiseOperator for LoanDataFlowOperator {
1477     #[inline]
1478     fn join(&self, succ: usize, pred: usize) -> usize {
1479         succ | pred // loans from both preds are in scope
1480     }
1481 }
1482
1483 impl DataFlowOperator for LoanDataFlowOperator {
1484     #[inline]
1485     fn initial_value(&self) -> bool {
1486         false // no loans in scope by default
1487     }
1488 }
1489
1490 impl<'tcx> fmt::Debug for InteriorKind {
1491     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1492         match *self {
1493             InteriorField(mc::FieldIndex(_, info)) => write!(f, "{}", info),
1494             InteriorElement => write!(f, "[]"),
1495         }
1496     }
1497 }
1498
1499 impl<'tcx> fmt::Debug for Loan<'tcx> {
1500     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1501         write!(f, "Loan_{}({:?}, {:?}, {:?}-{:?}, {:?})",
1502                self.index,
1503                self.loan_path,
1504                self.kind,
1505                self.gen_scope,
1506                self.kill_scope,
1507                self.restricted_paths)
1508     }
1509 }
1510
1511 impl<'tcx> fmt::Debug for LoanPath<'tcx> {
1512     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1513         match self.kind {
1514             LpVar(id) => {
1515                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().node_to_string(id)))
1516             }
1517
1518             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath {hir_id: var_id}, closure_expr_id }) => {
1519                 let s = ty::tls::with(|tcx| {
1520                     let var_node_id = tcx.hir().hir_to_node_id(var_id);
1521                     tcx.hir().node_to_string(var_node_id)
1522                 });
1523                 write!(f, "$({} captured by id={:?})", s, closure_expr_id)
1524             }
1525
1526             LpDowncast(ref lp, variant_def_id) => {
1527                 let variant_str = if variant_def_id.is_local() {
1528                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1529                 } else {
1530                     format!("{:?}", variant_def_id)
1531                 };
1532                 write!(f, "({:?}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1533             }
1534
1535             LpExtend(ref lp, _, LpDeref(_)) => {
1536                 write!(f, "{:?}.*", lp)
1537             }
1538
1539             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1540                 write!(f, "{:?}.{:?}", lp, interior)
1541             }
1542         }
1543     }
1544 }
1545
1546 impl<'tcx> fmt::Display for LoanPath<'tcx> {
1547     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1548         match self.kind {
1549             LpVar(id) => {
1550                 write!(f, "$({})", ty::tls::with(|tcx| tcx.hir().node_to_user_string(id)))
1551             }
1552
1553             LpUpvar(ty::UpvarId{ var_path: ty::UpvarPath { hir_id }, closure_expr_id: _ }) => {
1554                 let s = ty::tls::with(|tcx| {
1555                     let var_node_id = tcx.hir().hir_to_node_id(hir_id);
1556                     tcx.hir().node_to_string(var_node_id)
1557                 });
1558                 write!(f, "$({} captured by closure)", s)
1559             }
1560
1561             LpDowncast(ref lp, variant_def_id) => {
1562                 let variant_str = if variant_def_id.is_local() {
1563                     ty::tls::with(|tcx| tcx.item_path_str(variant_def_id))
1564                 } else {
1565                     format!("{:?}", variant_def_id)
1566                 };
1567                 write!(f, "({}{}{})", lp, DOWNCAST_PRINTED_OPERATOR, variant_str)
1568             }
1569
1570             LpExtend(ref lp, _, LpDeref(_)) => {
1571                 write!(f, "{}.*", lp)
1572             }
1573
1574             LpExtend(ref lp, _, LpInterior(_, ref interior)) => {
1575                 write!(f, "{}.{:?}", lp, interior)
1576             }
1577         }
1578     }
1579 }