src/librustc_borrowck/borrowck/check_loans.rs

   1 // Copyright 2012-2013 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 // ----------------------------------------------------------------------
  12 // Checking loans
  13 //
  14 // Phase 2 of check: we walk down the tree and check that:
  15 // 1. assignments are always made to mutable locations;
  16 // 2. loans made in overlapping scopes do not conflict
  17 // 3. assignments do not affect things loaned out as immutable
  18 // 4. moves do not affect things loaned out in any way
  19 use self::UseError::*;
  20
  21 use borrowck::*;
  22 use borrowck::InteriorKind::{InteriorElement, InteriorField};
  23 use rustc::middle::expr_use_visitor as euv;
  24 use rustc::middle::expr_use_visitor::MutateMode;
  25 use rustc::middle::mem_categorization as mc;
  26 use rustc::middle::mem_categorization::Categorization;
  27 use rustc::middle::region;
  28 use rustc::ty::{self, TyCtxt};
  29 use syntax::ast;
  30 use syntax_pos::Span;
  31 use rustc::hir;
  32 use rustc_mir::util::borrowck_errors::{BorrowckErrors, Origin};
  33
  34 use std::rc::Rc;
  35
  36 // FIXME (#16118): These functions are intended to allow the borrow checker to
  37 // be less precise in its handling of Box while still allowing moves out of a
  38 // Box. They should be removed when Unique is removed from LoanPath.
  39
  40 fn owned_ptr_base_path<'a, 'tcx>(loan_path: &'a LoanPath<'tcx>) -> &'a LoanPath<'tcx> {
  41     //! Returns the base of the leftmost dereference of an Unique in
  42     //! `loan_path`. If there is no dereference of an Unique in `loan_path`,
  43     //! then it just returns `loan_path` itself.
  44
  45     return match helper(loan_path) {
  46         Some(new_loan_path) => new_loan_path,
  47         None => loan_path.clone()
  48     };
  49
  50     fn helper<'a, 'tcx>(loan_path: &'a LoanPath<'tcx>) -> Option<&'a LoanPath<'tcx>> {
  51         match loan_path.kind {
  52             LpVar(_) | LpUpvar(_) => None,
  53             LpExtend(ref lp_base, _, LpDeref(mc::Unique)) => {
  54                 match helper(&lp_base) {
  55                     v @ Some(_) => v,
  56                     None => Some(&lp_base)
  57                 }
  58             }
  59             LpDowncast(ref lp_base, _) |
  60             LpExtend(ref lp_base, ..) => helper(&lp_base)
  61         }
  62     }
  63 }
  64
  65 fn owned_ptr_base_path_rc<'tcx>(loan_path: &Rc<LoanPath<'tcx>>) -> Rc<LoanPath<'tcx>> {
  66     //! The equivalent of `owned_ptr_base_path` for an &Rc<LoanPath> rather than
  67     //! a &LoanPath.
  68
  69     return match helper(loan_path) {
  70         Some(new_loan_path) => new_loan_path,
  71         None => loan_path.clone()
  72     };
  73
  74     fn helper<'tcx>(loan_path: &Rc<LoanPath<'tcx>>) -> Option<Rc<LoanPath<'tcx>>> {
  75         match loan_path.kind {
  76             LpVar(_) | LpUpvar(_) => None,
  77             LpExtend(ref lp_base, _, LpDeref(mc::Unique)) => {
  78                 match helper(lp_base) {
  79                     v @ Some(_) => v,
  80                     None => Some(lp_base.clone())
  81                 }
  82             }
  83             LpDowncast(ref lp_base, _) |
  84             LpExtend(ref lp_base, ..) => helper(lp_base)
  85         }
  86     }
  87 }
  88
  89 struct CheckLoanCtxt<'a, 'tcx: 'a> {
  90     bccx: &'a BorrowckCtxt<'a, 'tcx>,
  91     dfcx_loans: &'a LoanDataFlow<'a, 'tcx>,
  92     move_data: &'a move_data::FlowedMoveData<'a, 'tcx>,
  93     all_loans: &'a [Loan<'tcx>],
  94     param_env: ty::ParamEnv<'tcx>,
  95 }
  96
  97 impl<'a, 'tcx> euv::Delegate<'tcx> for CheckLoanCtxt<'a, 'tcx> {
  98     fn consume(&mut self,
  99                consume_id: ast::NodeId,
 100                consume_span: Span,
 101                cmt: mc::cmt<'tcx>,
 102                mode: euv::ConsumeMode) {
 103         debug!("consume(consume_id={}, cmt={:?}, mode={:?})",
 104                consume_id, cmt, mode);
 105
 106         let hir_id = self.tcx().hir.node_to_hir_id(consume_id);
 107         self.consume_common(hir_id.local_id, consume_span, cmt, mode);
 108     }
 109
 110     fn matched_pat(&mut self,
 111                    _matched_pat: &hir::Pat,
 112                    _cmt: mc::cmt,
 113                    _mode: euv::MatchMode) { }
 114
 115     fn consume_pat(&mut self,
 116                    consume_pat: &hir::Pat,
 117                    cmt: mc::cmt<'tcx>,
 118                    mode: euv::ConsumeMode) {
 119         debug!("consume_pat(consume_pat={:?}, cmt={:?}, mode={:?})",
 120                consume_pat,
 121                cmt,
 122                mode);
 123
 124         self.consume_common(consume_pat.hir_id.local_id, consume_pat.span, cmt, mode);
 125     }
 126
 127     fn borrow(&mut self,
 128               borrow_id: ast::NodeId,
 129               borrow_span: Span,
 130               cmt: mc::cmt<'tcx>,
 131               loan_region: ty::Region<'tcx>,
 132               bk: ty::BorrowKind,
 133               loan_cause: euv::LoanCause)
 134     {
 135         debug!("borrow(borrow_id={}, cmt={:?}, loan_region={:?}, \
 136                bk={:?}, loan_cause={:?})",
 137                borrow_id, cmt, loan_region,
 138                bk, loan_cause);
 139
 140         let hir_id = self.tcx().hir.node_to_hir_id(borrow_id);
 141         if let Some(lp) = opt_loan_path(&cmt) {
 142             let moved_value_use_kind = match loan_cause {
 143                 euv::ClosureCapture(_) => MovedInCapture,
 144                 _ => MovedInUse,
 145             };
 146             self.check_if_path_is_moved(hir_id.local_id, borrow_span, moved_value_use_kind, &lp);
 147         }
 148
 149         self.check_for_conflicting_loans(hir_id.local_id);
 150     }
 151
 152     fn mutate(&mut self,
 153               assignment_id: ast::NodeId,
 154               assignment_span: Span,
 155               assignee_cmt: mc::cmt<'tcx>,
 156               mode: euv::MutateMode)
 157     {
 158         debug!("mutate(assignment_id={}, assignee_cmt={:?})",
 159                assignment_id, assignee_cmt);
 160
 161         if let Some(lp) = opt_loan_path(&assignee_cmt) {
 162             match mode {
 163                 MutateMode::Init | MutateMode::JustWrite => {
 164                     // In a case like `path = 1`, then path does not
 165                     // have to be *FULLY* initialized, but we still
 166                     // must be careful lest it contains derefs of
 167                     // pointers.
 168                     let hir_id = self.tcx().hir.node_to_hir_id(assignee_cmt.id);
 169                     self.check_if_assigned_path_is_moved(hir_id.local_id,
 170                                                          assignment_span,
 171                                                          MovedInUse,
 172                                                          &lp);
 173                 }
 174                 MutateMode::WriteAndRead => {
 175                     // In a case like `path += 1`, then path must be
 176                     // fully initialized, since we will read it before
 177                     // we write it.
 178                     let hir_id = self.tcx().hir.node_to_hir_id(assignee_cmt.id);
 179                     self.check_if_path_is_moved(hir_id.local_id,
 180                                                 assignment_span,
 181                                                 MovedInUse,
 182                                                 &lp);
 183                 }
 184             }
 185         }
 186         self.check_assignment(self.tcx().hir.node_to_hir_id(assignment_id).local_id,
 187                               assignment_span, assignee_cmt);
 188     }
 189
 190     fn decl_without_init(&mut self, _id: ast::NodeId, _span: Span) { }
 191 }
 192
 193 pub fn check_loans<'a, 'b, 'c, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
 194                                      dfcx_loans: &LoanDataFlow<'b, 'tcx>,
 195                                      move_data: &move_data::FlowedMoveData<'c, 'tcx>,
 196                                      all_loans: &[Loan<'tcx>],
 197                                      body: &hir::Body) {
 198     debug!("check_loans(body id={})", body.value.id);
 199
 200     let def_id = bccx.tcx.hir.body_owner_def_id(body.id());
 201     let param_env = bccx.tcx.param_env(def_id);
 202     let mut clcx = CheckLoanCtxt {
 203         bccx,
 204         dfcx_loans,
 205         move_data,
 206         all_loans,
 207         param_env,
 208     };
 209     euv::ExprUseVisitor::new(&mut clcx, bccx.tcx, param_env, &bccx.region_scope_tree, bccx.tables)
 210         .consume_body(body);
 211 }
 212
 213 #[derive(PartialEq)]
 214 enum UseError<'tcx> {
 215     UseOk,
 216     UseWhileBorrowed(/*loan*/Rc<LoanPath<'tcx>>, /*loan*/Span)
 217 }
 218
 219 fn compatible_borrow_kinds(borrow_kind1: ty::BorrowKind,
 220                            borrow_kind2: ty::BorrowKind)
 221                            -> bool {
 222     borrow_kind1 == ty::ImmBorrow && borrow_kind2 == ty::ImmBorrow
 223 }
 224
 225 impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
 226     pub fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.bccx.tcx }
 227
 228     pub fn each_issued_loan<F>(&self, node: hir::ItemLocalId, mut op: F) -> bool where
 229         F: FnMut(&Loan<'tcx>) -> bool,
 230     {
 231         //! Iterates over each loan that has been issued
 232         //! on entrance to `node`, regardless of whether it is
 233         //! actually *in scope* at that point.  Sometimes loans
 234         //! are issued for future scopes and thus they may have been
 235         //! *issued* but not yet be in effect.
 236
 237         self.dfcx_loans.each_bit_on_entry(node, |loan_index| {
 238             let loan = &self.all_loans[loan_index];
 239             op(loan)
 240         })
 241     }
 242
 243     pub fn each_in_scope_loan<F>(&self, scope: region::Scope, mut op: F) -> bool where
 244         F: FnMut(&Loan<'tcx>) -> bool,
 245     {
 246         //! Like `each_issued_loan()`, but only considers loans that are
 247         //! currently in scope.
 248
 249         self.each_issued_loan(scope.item_local_id(), |loan| {
 250             if self.bccx.region_scope_tree.is_subscope_of(scope, loan.kill_scope) {
 251                 op(loan)
 252             } else {
 253                 true
 254             }
 255         })
 256     }
 257
 258     fn each_in_scope_loan_affecting_path<F>(&self,
 259                                             scope: region::Scope,
 260                                             loan_path: &LoanPath<'tcx>,
 261                                             mut op: F)
 262                                             -> bool where
 263         F: FnMut(&Loan<'tcx>) -> bool,
 264     {
 265         //! Iterates through all of the in-scope loans affecting `loan_path`,
 266         //! calling `op`, and ceasing iteration if `false` is returned.
 267
 268         // First, we check for a loan restricting the path P being used. This
 269         // accounts for borrows of P but also borrows of subpaths, like P.a.b.
 270         // Consider the following example:
 271         //
 272         //     let x = &mut a.b.c; // Restricts a, a.b, and a.b.c
 273         //     let y = a;          // Conflicts with restriction
 274
 275         let loan_path = owned_ptr_base_path(loan_path);
 276         let cont = self.each_in_scope_loan(scope, |loan| {
 277             let mut ret = true;
 278             for restr_path in &loan.restricted_paths {
 279                 if **restr_path == *loan_path {
 280                     if !op(loan) {
 281                         ret = false;
 282                         break;
 283                     }
 284                 }
 285             }
 286             ret
 287         });
 288
 289         if !cont {
 290             return false;
 291         }
 292
 293         // Next, we must check for *loans* (not restrictions) on the path P or
 294         // any base path. This rejects examples like the following:
 295         //
 296         //     let x = &mut a.b;
 297         //     let y = a.b.c;
 298         //
 299         // Limiting this search to *loans* and not *restrictions* means that
 300         // examples like the following continue to work:
 301         //
 302         //     let x = &mut a.b;
 303         //     let y = a.c;
 304
 305         let mut loan_path = loan_path;
 306         loop {
 307             match loan_path.kind {
 308                 LpVar(_) | LpUpvar(_) => {
 309                     break;
 310                 }
 311                 LpDowncast(ref lp_base, _) |
 312                 LpExtend(ref lp_base, ..) => {
 313                     loan_path = &lp_base;
 314                 }
 315             }
 316
 317             let cont = self.each_in_scope_loan(scope, |loan| {
 318                 if *loan.loan_path == *loan_path {
 319                     op(loan)
 320                 } else {
 321                     true
 322                 }
 323             });
 324
 325             if !cont {
 326                 return false;
 327             }
 328         }
 329
 330         return true;
 331     }
 332
 333     pub fn loans_generated_by(&self, node: hir::ItemLocalId) -> Vec<usize> {
 334         //! Returns a vector of the loans that are generated as
 335         //! we enter `node`.
 336
 337         let mut result = Vec::new();
 338         self.dfcx_loans.each_gen_bit(node, |loan_index| {
 339             result.push(loan_index);
 340             true
 341         });
 342         return result;
 343     }
 344
 345     pub fn check_for_conflicting_loans(&self, node: hir::ItemLocalId) {
 346         //! Checks to see whether any of the loans that are issued
 347         //! on entrance to `node` conflict with loans that have already been
 348         //! issued when we enter `node` (for example, we do not
 349         //! permit two `&mut` borrows of the same variable).
 350         //!
 351         //! (Note that some loans can be *issued* without necessarily
 352         //! taking effect yet.)
 353
 354         debug!("check_for_conflicting_loans(node={:?})", node);
 355
 356         let new_loan_indices = self.loans_generated_by(node);
 357         debug!("new_loan_indices = {:?}", new_loan_indices);
 358
 359         for &new_loan_index in &new_loan_indices {
 360             self.each_issued_loan(node, |issued_loan| {
 361                 let new_loan = &self.all_loans[new_loan_index];
 362                 // Only report an error for the first issued loan that conflicts
 363                 // to avoid O(n^2) errors.
 364                 self.report_error_if_loans_conflict(issued_loan, new_loan)
 365             });
 366         }
 367
 368         for (i, &x) in new_loan_indices.iter().enumerate() {
 369             let old_loan = &self.all_loans[x];
 370             for &y in &new_loan_indices[(i+1) ..] {
 371                 let new_loan = &self.all_loans[y];
 372                 self.report_error_if_loans_conflict(old_loan, new_loan);
 373             }
 374         }
 375     }
 376
 377     pub fn report_error_if_loans_conflict(&self,
 378                                           old_loan: &Loan<'tcx>,
 379                                           new_loan: &Loan<'tcx>)
 380                                           -> bool {
 381         //! Checks whether `old_loan` and `new_loan` can safely be issued
 382         //! simultaneously.
 383
 384         debug!("report_error_if_loans_conflict(old_loan={:?}, new_loan={:?})",
 385                old_loan,
 386                new_loan);
 387
 388         // Should only be called for loans that are in scope at the same time.
 389         assert!(self.bccx.region_scope_tree.scopes_intersect(old_loan.kill_scope,
 390                                                        new_loan.kill_scope));
 391
 392         self.report_error_if_loan_conflicts_with_restriction(
 393             old_loan, new_loan, old_loan, new_loan) &&
 394         self.report_error_if_loan_conflicts_with_restriction(
 395             new_loan, old_loan, old_loan, new_loan)
 396     }
 397
 398     pub fn report_error_if_loan_conflicts_with_restriction(&self,
 399                                                            loan1: &Loan<'tcx>,
 400                                                            loan2: &Loan<'tcx>,
 401                                                            old_loan: &Loan<'tcx>,
 402                                                            new_loan: &Loan<'tcx>)
 403                                                            -> bool {
 404         //! Checks whether the restrictions introduced by `loan1` would
 405         //! prohibit `loan2`. Returns false if an error is reported.
 406
 407         debug!("report_error_if_loan_conflicts_with_restriction(\
 408                 loan1={:?}, loan2={:?})",
 409                loan1,
 410                loan2);
 411
 412         if compatible_borrow_kinds(loan1.kind, loan2.kind) {
 413             return true;
 414         }
 415
 416         let loan2_base_path = owned_ptr_base_path_rc(&loan2.loan_path);
 417         for restr_path in &loan1.restricted_paths {
 418             if *restr_path != loan2_base_path { continue; }
 419
 420             // If new_loan is something like `x.a`, and old_loan is something like `x.b`, we would
 421             // normally generate a rather confusing message (in this case, for multiple mutable
 422             // borrows):
 423             //
 424             //     error: cannot borrow `x.b` as mutable more than once at a time
 425             //     note: previous borrow of `x.a` occurs here; the mutable borrow prevents
 426             //     subsequent moves, borrows, or modification of `x.a` until the borrow ends
 427             //
 428             // What we want to do instead is get the 'common ancestor' of the two borrow paths and
 429             // use that for most of the message instead, giving is something like this:
 430             //
 431             //     error: cannot borrow `x` as mutable more than once at a time
 432             //     note: previous borrow of `x` occurs here (through borrowing `x.a`); the mutable
 433             //     borrow prevents subsequent moves, borrows, or modification of `x` until the
 434             //     borrow ends
 435
 436             let common = new_loan.loan_path.common(&old_loan.loan_path);
 437             let (nl, ol, new_loan_msg, old_loan_msg) = {
 438                 if new_loan.loan_path.has_fork(&old_loan.loan_path) && common.is_some() {
 439                     let nl = self.bccx.loan_path_to_string(&common.unwrap());
 440                     let ol = nl.clone();
 441                     let new_loan_msg = format!(" (via `{}`)",
 442                                                self.bccx.loan_path_to_string(
 443                                                    &new_loan.loan_path));
 444                     let old_loan_msg = format!(" (via `{}`)",
 445                                                self.bccx.loan_path_to_string(
 446                                                    &old_loan.loan_path));
 447                     (nl, ol, new_loan_msg, old_loan_msg)
 448                 } else {
 449                     (self.bccx.loan_path_to_string(&new_loan.loan_path),
 450                      self.bccx.loan_path_to_string(&old_loan.loan_path),
 451                      String::new(),
 452                      String::new())
 453                 }
 454             };
 455
 456             let ol_pronoun = if new_loan.loan_path == old_loan.loan_path {
 457                 "it".to_string()
 458             } else {
 459                 format!("`{}`", ol)
 460             };
 461
 462             // We want to assemble all the relevant locations for the error.
 463             //
 464             // 1. Where did the new loan occur.
 465             //    - if due to closure creation, where was the variable used in closure?
 466             // 2. Where did old loan occur.
 467             // 3. Where does old loan expire.
 468
 469             let previous_end_span =
 470                 old_loan.kill_scope.span(self.tcx(), &self.bccx.region_scope_tree).end_point();
 471
 472             let mut err = match (new_loan.kind, old_loan.kind) {
 473                 (ty::MutBorrow, ty::MutBorrow) =>
 474                     self.bccx.cannot_mutably_borrow_multiply(
 475                         new_loan.span, &nl, &new_loan_msg, old_loan.span, &old_loan_msg,
 476                         previous_end_span, Origin::Ast),
 477                 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) =>
 478                     self.bccx.cannot_uniquely_borrow_by_two_closures(
 479                         new_loan.span, &nl, old_loan.span, previous_end_span, Origin::Ast),
 480                 (ty::UniqueImmBorrow, _) =>
 481                     self.bccx.cannot_uniquely_borrow_by_one_closure(
 482                         new_loan.span, &nl, &new_loan_msg,
 483                         old_loan.span, &ol_pronoun, &old_loan_msg, previous_end_span, Origin::Ast),
 484                 (_, ty::UniqueImmBorrow) => {
 485                     let new_loan_str = &new_loan.kind.to_user_str();
 486                     self.bccx.cannot_reborrow_already_uniquely_borrowed(
 487                         new_loan.span, &nl, &new_loan_msg, new_loan_str,
 488                         old_loan.span, &old_loan_msg, previous_end_span, Origin::Ast)
 489                 }
 490                 (..) =>
 491                     self.bccx.cannot_reborrow_already_borrowed(
 492                         new_loan.span,
 493                         &nl, &new_loan_msg, &new_loan.kind.to_user_str(),
 494                         old_loan.span, &ol_pronoun, &old_loan.kind.to_user_str(), &old_loan_msg,
 495                         previous_end_span, Origin::Ast)
 496             };
 497
 498             match new_loan.cause {
 499                 euv::ClosureCapture(span) => {
 500                     err.span_label(
 501                         span,
 502                         format!("borrow occurs due to use of `{}` in closure", nl));
 503                 }
 504                 _ => { }
 505             }
 506
 507             match old_loan.cause {
 508                 euv::ClosureCapture(span) => {
 509                     err.span_label(
 510                         span,
 511                         format!("previous borrow occurs due to use of `{}` in closure",
 512                                  ol));
 513                 }
 514                 _ => { }
 515             }
 516
 517             err.emit();
 518             return false;
 519         }
 520
 521         true
 522     }
 523
 524     fn consume_common(&self,
 525                       id: hir::ItemLocalId,
 526                       span: Span,
 527                       cmt: mc::cmt<'tcx>,
 528                       mode: euv::ConsumeMode) {
 529         if let Some(lp) = opt_loan_path(&cmt) {
 530             let moved_value_use_kind = match mode {
 531                 euv::Copy => {
 532                     self.check_for_copy_of_frozen_path(id, span, &lp);
 533                     MovedInUse
 534                 }
 535                 euv::Move(_) => {
 536                     match self.move_data.kind_of_move_of_path(id, &lp) {
 537                         None => {
 538                             // Sometimes moves don't have a move kind;
 539                             // this either means that the original move
 540                             // was from something illegal to move,
 541                             // or was moved from referent of an unsafe
 542                             // pointer or something like that.
 543                             MovedInUse
 544                         }
 545                         Some(move_kind) => {
 546                             self.check_for_move_of_borrowed_path(id, span,
 547                                                                  &lp, move_kind);
 548                             if move_kind == move_data::Captured {
 549                                 MovedInCapture
 550                             } else {
 551                                 MovedInUse
 552                             }
 553                         }
 554                     }
 555                 }
 556             };
 557
 558             self.check_if_path_is_moved(id, span, moved_value_use_kind, &lp);
 559         }
 560     }
 561
 562     fn check_for_copy_of_frozen_path(&self,
 563                                      id: hir::ItemLocalId,
 564                                      span: Span,
 565                                      copy_path: &LoanPath<'tcx>) {
 566         match self.analyze_restrictions_on_use(id, copy_path, ty::ImmBorrow) {
 567             UseOk => { }
 568             UseWhileBorrowed(loan_path, loan_span) => {
 569                 let desc = self.bccx.loan_path_to_string(copy_path);
 570                 self.bccx.cannot_use_when_mutably_borrowed(
 571                         span, &desc,
 572                         loan_span, &self.bccx.loan_path_to_string(&loan_path),
 573                         Origin::Ast)
 574                     .emit();
 575             }
 576         }
 577     }
 578
 579     fn check_for_move_of_borrowed_path(&self,
 580                                        id: hir::ItemLocalId,
 581                                        span: Span,
 582                                        move_path: &LoanPath<'tcx>,
 583                                        move_kind: move_data::MoveKind) {
 584         // We want to detect if there are any loans at all, so we search for
 585         // any loans incompatible with MutBorrrow, since all other kinds of
 586         // loans are incompatible with that.
 587         match self.analyze_restrictions_on_use(id, move_path, ty::MutBorrow) {
 588             UseOk => { }
 589             UseWhileBorrowed(loan_path, loan_span) => {
 590                 let mut err = match move_kind {
 591                     move_data::Captured => {
 592                         let mut err = self.bccx.cannot_move_into_closure(
 593                             span, &self.bccx.loan_path_to_string(move_path), Origin::Ast);
 594                         err.span_label(
 595                             loan_span,
 596                             format!("borrow of `{}` occurs here",
 597                                     &self.bccx.loan_path_to_string(&loan_path))
 598                             );
 599                         err.span_label(
 600                             span,
 601                             "move into closure occurs here"
 602                             );
 603                         err
 604                     }
 605                     move_data::Declared |
 606                     move_data::MoveExpr |
 607                     move_data::MovePat => {
 608                         let desc = self.bccx.loan_path_to_string(move_path);
 609                         let mut err = self.bccx.cannot_move_when_borrowed(span, &desc, Origin::Ast);
 610                         err.span_label(
 611                             loan_span,
 612                             format!("borrow of `{}` occurs here",
 613                                     &self.bccx.loan_path_to_string(&loan_path))
 614                             );
 615                         err.span_label(
 616                             span,
 617                             format!("move out of `{}` occurs here",
 618                                 &self.bccx.loan_path_to_string(move_path))
 619                             );
 620                         err
 621                     }
 622                 };
 623
 624                 err.emit();
 625             }
 626         }
 627     }
 628
 629     pub fn analyze_restrictions_on_use(&self,
 630                                        expr_id: hir::ItemLocalId,
 631                                        use_path: &LoanPath<'tcx>,
 632                                        borrow_kind: ty::BorrowKind)
 633                                        -> UseError<'tcx> {
 634         debug!("analyze_restrictions_on_use(expr_id={:?}, use_path={:?})",
 635                expr_id, use_path);
 636
 637         let mut ret = UseOk;
 638
 639         self.each_in_scope_loan_affecting_path(
 640             region::Scope::Node(expr_id), use_path, |loan| {
 641             if !compatible_borrow_kinds(loan.kind, borrow_kind) {
 642                 ret = UseWhileBorrowed(loan.loan_path.clone(), loan.span);
 643                 false
 644             } else {
 645                 true
 646             }
 647         });
 648
 649         return ret;
 650     }
 651
 652     /// Reports an error if `expr` (which should be a path)
 653     /// is using a moved/uninitialized value
 654     fn check_if_path_is_moved(&self,
 655                               id: hir::ItemLocalId,
 656                               span: Span,
 657                               use_kind: MovedValueUseKind,
 658                               lp: &Rc<LoanPath<'tcx>>) {
 659         debug!("check_if_path_is_moved(id={:?}, use_kind={:?}, lp={:?})",
 660                id, use_kind, lp);
 661
 662         // FIXME: if you find yourself tempted to cut and paste
 663         // the body below and then specializing the error reporting,
 664         // consider refactoring this instead!
 665
 666         let base_lp = owned_ptr_base_path_rc(lp);
 667         self.move_data.each_move_of(id, &base_lp, |the_move, moved_lp| {
 668             self.bccx.report_use_of_moved_value(
 669                 span,
 670                 use_kind,
 671                 &lp,
 672                 the_move,
 673                 moved_lp,
 674                 self.param_env);
 675             false
 676         });
 677     }
 678
 679     /// Reports an error if assigning to `lp` will use a
 680     /// moved/uninitialized value. Mainly this is concerned with
 681     /// detecting derefs of uninitialized pointers.
 682     ///
 683     /// For example:
 684     ///
 685     /// ```
 686     /// let a: i32;
 687     /// a = 10; // ok, even though a is uninitialized
 688     /// ```
 689     ///
 690     /// ```
 691     /// struct Point { x: u32, y: u32 }
 692     /// let mut p: Point;
 693     /// p.x = 22; // ok, even though `p` is uninitialized
 694     /// ```
 695     ///
 696     /// ```compile_fail,E0381
 697     /// # struct Point { x: u32, y: u32 }
 698     /// let mut p: Box<Point>;
 699     /// (*p).x = 22; // not ok, p is uninitialized, can't deref
 700     /// ```
 701     fn check_if_assigned_path_is_moved(&self,
 702                                        id: hir::ItemLocalId,
 703                                        span: Span,
 704                                        use_kind: MovedValueUseKind,
 705                                        lp: &Rc<LoanPath<'tcx>>)
 706     {
 707         match lp.kind {
 708             LpVar(_) | LpUpvar(_) => {
 709                 // assigning to `x` does not require that `x` is initialized
 710             }
 711             LpDowncast(ref lp_base, _) => {
 712                 // assigning to `(P->Variant).f` is ok if assigning to `P` is ok
 713                 self.check_if_assigned_path_is_moved(id, span,
 714                                                      use_kind, lp_base);
 715             }
 716             LpExtend(ref lp_base, _, LpInterior(_, InteriorField(_))) => {
 717                 match lp_base.to_type().sty {
 718                     ty::TyAdt(def, _) if def.has_dtor(self.tcx()) => {
 719                         // In the case where the owner implements drop, then
 720                         // the path must be initialized to prevent a case of
 721                         // partial reinitialization
 722                         //
 723                         // FIXME: could refactor via hypothetical
 724                         // generalized check_if_path_is_moved
 725                         let loan_path = owned_ptr_base_path_rc(lp_base);
 726                         self.move_data.each_move_of(id, &loan_path, |_, _| {
 727                             self.bccx
 728                                 .report_partial_reinitialization_of_uninitialized_structure(
 729                                     span,
 730                                     &loan_path);
 731                             false
 732                         });
 733                         return;
 734                     },
 735                     _ => {},
 736                 }
 737
 738                 // assigning to `P.f` is ok if assigning to `P` is ok
 739                 self.check_if_assigned_path_is_moved(id, span,
 740                                                      use_kind, lp_base);
 741             }
 742             LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) |
 743             LpExtend(ref lp_base, _, LpDeref(_)) => {
 744                 // assigning to `P[i]` requires `P` is initialized
 745                 // assigning to `(*P)` requires `P` is initialized
 746                 self.check_if_path_is_moved(id, span, use_kind, lp_base);
 747             }
 748         }
 749     }
 750
 751     fn check_assignment(&self,
 752                         assignment_id: hir::ItemLocalId,
 753                         assignment_span: Span,
 754                         assignee_cmt: mc::cmt<'tcx>) {
 755         debug!("check_assignment(assignee_cmt={:?})", assignee_cmt);
 756
 757         // Check that we don't invalidate any outstanding loans
 758         if let Some(loan_path) = opt_loan_path(&assignee_cmt) {
 759             let scope = region::Scope::Node(assignment_id);
 760             self.each_in_scope_loan_affecting_path(scope, &loan_path, |loan| {
 761                 self.report_illegal_mutation(assignment_span, &loan_path, loan);
 762                 false
 763             });
 764         }
 765
 766         // Check for reassignments to (immutable) local variables. This
 767         // needs to be done here instead of in check_loans because we
 768         // depend on move data.
 769         if let Categorization::Local(local_id) = assignee_cmt.cat {
 770             let lp = opt_loan_path(&assignee_cmt).unwrap();
 771             self.move_data.each_assignment_of(assignment_id, &lp, |assign| {
 772                 if assignee_cmt.mutbl.is_mutable() {
 773                     let hir_id = self.bccx.tcx.hir.node_to_hir_id(local_id);
 774                     self.bccx.used_mut_nodes.borrow_mut().insert(hir_id);
 775                 } else {
 776                     self.bccx.report_reassigned_immutable_variable(
 777                         assignment_span,
 778                         &lp,
 779                         assign);
 780                 }
 781                 false
 782             });
 783             return
 784         }
 785     }
 786
 787     pub fn report_illegal_mutation(&self,
 788                                    span: Span,
 789                                    loan_path: &LoanPath<'tcx>,
 790                                    loan: &Loan) {
 791         self.bccx.cannot_assign_to_borrowed(
 792             span, loan.span, &self.bccx.loan_path_to_string(loan_path), Origin::Ast)
 793             .emit();
 794     }
 795 }