src/librustc_typeck/check/upvar.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! ### Inferring borrow kinds for upvars
  12 //!
  13 //! Whenever there is a closure expression, we need to determine how each
  14 //! upvar is used. We do this by initially assigning each upvar an
  15 //! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
  16 //! "escalating" the kind as needed. The borrow kind proceeds according to
  17 //! the following lattice:
  18 //!
  19 //!     ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
  20 //!
  21 //! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
  22 //! will promote its borrow kind to mutable borrow. If we see an `&mut x`
  23 //! we'll do the same. Naturally, this applies not just to the upvar, but
  24 //! to everything owned by `x`, so the result is the same for something
  25 //! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
  26 //! struct). These adjustments are performed in
  27 //! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
  28 //! from there).
  29 //!
  30 //! The fact that we are inferring borrow kinds as we go results in a
  31 //! semi-hacky interaction with mem-categorization. In particular,
  32 //! mem-categorization will query the current borrow kind as it
  33 //! categorizes, and we'll return the *current* value, but this may get
  34 //! adjusted later. Therefore, in this module, we generally ignore the
  35 //! borrow kind (and derived mutabilities) that are returned from
  36 //! mem-categorization, since they may be inaccurate. (Another option
  37 //! would be to use a unification scheme, where instead of returning a
  38 //! concrete borrow kind like `ty::ImmBorrow`, we return a
  39 //! `ty::InferBorrow(upvar_id)` or something like that, but this would
  40 //! then mean that all later passes would have to check for these figments
  41 //! and report an error, and it just seems like more mess in the end.)
  42
  43 use super::FnCtxt;
  44
  45 use check::demand;
  46 use middle::expr_use_visitor as euv;
  47 use middle::mem_categorization as mc;
  48 use middle::mem_categorization::Categorization;
  49 use middle::ty::{self, Ty};
  50 use middle::infer::{InferCtxt, UpvarRegion};
  51 use std::collections::HashSet;
  52 use syntax::ast;
  53 use syntax::codemap::Span;
  54 use rustc_front::hir;
  55 use rustc_front::intravisit::{self, Visitor};
  56
  57 ///////////////////////////////////////////////////////////////////////////
  58 // PUBLIC ENTRY POINTS
  59
  60 pub fn closure_analyze_fn(fcx: &FnCtxt,
  61                           _id: ast::NodeId,
  62                           _decl: &hir::FnDecl,
  63                           body: &hir::Block)
  64 {
  65     let mut seed = SeedBorrowKind::new(fcx);
  66     seed.visit_block(body);
  67     let closures_with_inferred_kinds = seed.closures_with_inferred_kinds;
  68
  69     let mut adjust = AdjustBorrowKind::new(fcx, &closures_with_inferred_kinds);
  70     adjust.visit_block(body);
  71
  72     // it's our job to process these.
  73     assert!(fcx.inh.deferred_call_resolutions.borrow().is_empty());
  74 }
  75
  76 pub fn closure_analyze_const(fcx: &FnCtxt,
  77                              body: &hir::Expr)
  78 {
  79     let mut seed = SeedBorrowKind::new(fcx);
  80     seed.visit_expr(body);
  81     let closures_with_inferred_kinds = seed.closures_with_inferred_kinds;
  82
  83     let mut adjust = AdjustBorrowKind::new(fcx, &closures_with_inferred_kinds);
  84     adjust.visit_expr(body);
  85
  86     // it's our job to process these.
  87     assert!(fcx.inh.deferred_call_resolutions.borrow().is_empty());
  88 }
  89
  90 ///////////////////////////////////////////////////////////////////////////
  91 // SEED BORROW KIND
  92
  93 struct SeedBorrowKind<'a,'tcx:'a> {
  94     fcx: &'a FnCtxt<'a,'tcx>,
  95     closures_with_inferred_kinds: HashSet<ast::NodeId>,
  96 }
  97
  98 impl<'a, 'tcx, 'v> Visitor<'v> for SeedBorrowKind<'a, 'tcx> {
  99     fn visit_expr(&mut self, expr: &hir::Expr) {
 100         match expr.node {
 101             hir::ExprClosure(cc, _, ref body) => {
 102                 self.check_closure(expr, cc, &**body);
 103             }
 104
 105             _ => { }
 106         }
 107
 108         intravisit::walk_expr(self, expr);
 109     }
 110 }
 111
 112 impl<'a,'tcx> SeedBorrowKind<'a,'tcx> {
 113     fn new(fcx: &'a FnCtxt<'a,'tcx>) -> SeedBorrowKind<'a,'tcx> {
 114         SeedBorrowKind { fcx: fcx, closures_with_inferred_kinds: HashSet::new() }
 115     }
 116
 117     fn tcx(&self) -> &'a ty::ctxt<'tcx> {
 118         self.fcx.tcx()
 119     }
 120
 121     fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
 122         self.fcx.infcx()
 123     }
 124
 125     fn check_closure(&mut self,
 126                      expr: &hir::Expr,
 127                      capture_clause: hir::CaptureClause,
 128                      _body: &hir::Block)
 129     {
 130         let closure_def_id = self.tcx().map.local_def_id(expr.id);
 131         if !self.fcx.inh.tables.borrow().closure_kinds.contains_key(&closure_def_id) {
 132             self.closures_with_inferred_kinds.insert(expr.id);
 133             self.fcx.inh.tables.borrow_mut().closure_kinds
 134                                             .insert(closure_def_id, ty::FnClosureKind);
 135             debug!("check_closure: adding closure_id={:?} to closures_with_inferred_kinds",
 136                    closure_def_id);
 137         }
 138
 139         self.tcx().with_freevars(expr.id, |freevars| {
 140             for freevar in freevars {
 141                 let var_node_id = freevar.def.var_id();
 142                 let upvar_id = ty::UpvarId { var_id: var_node_id,
 143                                              closure_expr_id: expr.id };
 144                 debug!("seed upvar_id {:?}", upvar_id);
 145
 146                 let capture_kind = match capture_clause {
 147                     hir::CaptureByValue => {
 148                         ty::UpvarCapture::ByValue
 149                     }
 150                     hir::CaptureByRef => {
 151                         let origin = UpvarRegion(upvar_id, expr.span);
 152                         let freevar_region = self.infcx().next_region_var(origin);
 153                         let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
 154                                                              region: freevar_region };
 155                         ty::UpvarCapture::ByRef(upvar_borrow)
 156                     }
 157                 };
 158
 159                 self.fcx.inh.tables.borrow_mut().upvar_capture_map.insert(upvar_id, capture_kind);
 160             }
 161         });
 162     }
 163 }
 164
 165 ///////////////////////////////////////////////////////////////////////////
 166 // ADJUST BORROW KIND
 167
 168 struct AdjustBorrowKind<'a,'tcx:'a> {
 169     fcx: &'a FnCtxt<'a,'tcx>,
 170     closures_with_inferred_kinds: &'a HashSet<ast::NodeId>,
 171 }
 172
 173 impl<'a,'tcx> AdjustBorrowKind<'a,'tcx> {
 174     fn new(fcx: &'a FnCtxt<'a,'tcx>,
 175            closures_with_inferred_kinds: &'a HashSet<ast::NodeId>)
 176            -> AdjustBorrowKind<'a,'tcx> {
 177         AdjustBorrowKind { fcx: fcx, closures_with_inferred_kinds: closures_with_inferred_kinds }
 178     }
 179
 180     fn analyze_closure(&mut self,
 181                        id: ast::NodeId,
 182                        span: Span,
 183                        decl: &hir::FnDecl,
 184                        body: &hir::Block) {
 185         /*!
 186          * Analysis starting point.
 187          */
 188
 189         debug!("analyze_closure(id={:?}, body.id={:?})", id, body.id);
 190
 191         {
 192             let mut euv = euv::ExprUseVisitor::new(self, self.fcx.infcx());
 193             euv.walk_fn(decl, body);
 194         }
 195
 196         // Now that we've analyzed the closure, we know how each
 197         // variable is borrowed, and we know what traits the closure
 198         // implements (Fn vs FnMut etc). We now have some updates to do
 199         // with that information.
 200         //
 201         // Note that no closure type C may have an upvar of type C
 202         // (though it may reference itself via a trait object). This
 203         // results from the desugaring of closures to a struct like
 204         // `Foo<..., UV0...UVn>`. If one of those upvars referenced
 205         // C, then the type would have infinite size (and the
 206         // inference algorithm will reject it).
 207
 208         // Extract the type variables UV0...UVn.
 209         let closure_substs = match self.fcx.node_ty(id).sty {
 210             ty::TyClosure(_, ref substs) => substs,
 211             ref t => {
 212                 self.fcx.tcx().sess.span_bug(
 213                     span,
 214                     &format!("type of closure expr {:?} is not a closure {:?}",
 215                              id, t));
 216             }
 217         };
 218
 219         // Equate the type variables with the actual types.
 220         let final_upvar_tys = self.final_upvar_tys(id);
 221         debug!("analyze_closure: id={:?} closure_substs={:?} final_upvar_tys={:?}",
 222                id, closure_substs, final_upvar_tys);
 223         for (&upvar_ty, final_upvar_ty) in closure_substs.upvar_tys.iter().zip(final_upvar_tys) {
 224             demand::eqtype(self.fcx, span, final_upvar_ty, upvar_ty);
 225         }
 226
 227         // Now we must process and remove any deferred resolutions,
 228         // since we have a concrete closure kind.
 229         let closure_def_id = self.fcx.tcx().map.local_def_id(id);
 230         if self.closures_with_inferred_kinds.contains(&id) {
 231             let mut deferred_call_resolutions =
 232                 self.fcx.remove_deferred_call_resolutions(closure_def_id);
 233             for deferred_call_resolution in &mut deferred_call_resolutions {
 234                 deferred_call_resolution.resolve(self.fcx);
 235             }
 236         }
 237     }
 238
 239     // Returns a list of `ClosureUpvar`s for each upvar.
 240     fn final_upvar_tys(&mut self, closure_id: ast::NodeId) -> Vec<Ty<'tcx>> {
 241         // Presently an unboxed closure type cannot "escape" out of a
 242         // function, so we will only encounter ones that originated in the
 243         // local crate or were inlined into it along with some function.
 244         // This may change if abstract return types of some sort are
 245         // implemented.
 246         let tcx = self.fcx.tcx();
 247         tcx.with_freevars(closure_id, |freevars| {
 248             freevars.iter()
 249                     .map(|freevar| {
 250                         let freevar_node_id = freevar.def.var_id();
 251                         let freevar_ty = self.fcx.node_ty(freevar_node_id);
 252                         let upvar_id = ty::UpvarId {
 253                             var_id: freevar_node_id,
 254                             closure_expr_id: closure_id
 255                         };
 256                         let capture = self.fcx.infcx().upvar_capture(upvar_id).unwrap();
 257
 258                         debug!("freevar_node_id={:?} freevar_ty={:?} capture={:?}",
 259                                freevar_node_id, freevar_ty, capture);
 260
 261                         match capture {
 262                             ty::UpvarCapture::ByValue => freevar_ty,
 263                             ty::UpvarCapture::ByRef(borrow) =>
 264                                 tcx.mk_ref(tcx.mk_region(borrow.region),
 265                                            ty::TypeAndMut {
 266                                                ty: freevar_ty,
 267                                                mutbl: borrow.kind.to_mutbl_lossy(),
 268                                            }),
 269                         }
 270                     })
 271                     .collect()
 272             })
 273     }
 274
 275     fn adjust_upvar_borrow_kind_for_consume(&self,
 276                                             cmt: mc::cmt<'tcx>,
 277                                             mode: euv::ConsumeMode)
 278     {
 279         debug!("adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
 280                cmt, mode);
 281
 282         // we only care about moves
 283         match mode {
 284             euv::Copy => { return; }
 285             euv::Move(_) => { }
 286         }
 287
 288         // watch out for a move of the deref of a borrowed pointer;
 289         // for that to be legal, the upvar would have to be borrowed
 290         // by value instead
 291         let guarantor = cmt.guarantor();
 292         debug!("adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
 293                guarantor);
 294         match guarantor.cat {
 295             Categorization::Deref(_, _, mc::BorrowedPtr(..)) |
 296             Categorization::Deref(_, _, mc::Implicit(..)) => {
 297                 match cmt.note {
 298                     mc::NoteUpvarRef(upvar_id) => {
 299                         debug!("adjust_upvar_borrow_kind_for_consume: \
 300                                 setting upvar_id={:?} to by value",
 301                                upvar_id);
 302
 303                         // to move out of an upvar, this must be a FnOnce closure
 304                         self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
 305
 306                         let upvar_capture_map =
 307                             &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
 308                         upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
 309                     }
 310                     mc::NoteClosureEnv(upvar_id) => {
 311                         // we get just a closureenv ref if this is a
 312                         // `move` closure, or if the upvar has already
 313                         // been inferred to by-value. In any case, we
 314                         // must still adjust the kind of the closure
 315                         // to be a FnOnce closure to permit moves out
 316                         // of the environment.
 317                         self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
 318                     }
 319                     mc::NoteNone => {
 320                     }
 321                 }
 322             }
 323             _ => { }
 324         }
 325     }
 326
 327     /// Indicates that `cmt` is being directly mutated (e.g., assigned
 328     /// to). If cmt contains any by-ref upvars, this implies that
 329     /// those upvars must be borrowed using an `&mut` borrow.
 330     fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
 331         debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})",
 332                cmt);
 333
 334         match cmt.cat.clone() {
 335             Categorization::Deref(base, _, mc::Unique) |
 336             Categorization::Interior(base, _) |
 337             Categorization::Downcast(base, _) => {
 338                 // Interior or owned data is mutable if base is
 339                 // mutable, so iterate to the base.
 340                 self.adjust_upvar_borrow_kind_for_mut(base);
 341             }
 342
 343             Categorization::Deref(base, _, mc::BorrowedPtr(..)) |
 344             Categorization::Deref(base, _, mc::Implicit(..)) => {
 345                 if !self.try_adjust_upvar_deref(&cmt.note, ty::MutBorrow) {
 346                     // assignment to deref of an `&mut`
 347                     // borrowed pointer implies that the
 348                     // pointer itself must be unique, but not
 349                     // necessarily *mutable*
 350                     self.adjust_upvar_borrow_kind_for_unique(base);
 351                 }
 352             }
 353
 354             Categorization::Deref(_, _, mc::UnsafePtr(..)) |
 355             Categorization::StaticItem |
 356             Categorization::Rvalue(_) |
 357             Categorization::Local(_) |
 358             Categorization::Upvar(..) => {
 359                 return;
 360             }
 361         }
 362     }
 363
 364     fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
 365         debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})",
 366                cmt);
 367
 368         match cmt.cat.clone() {
 369             Categorization::Deref(base, _, mc::Unique) |
 370             Categorization::Interior(base, _) |
 371             Categorization::Downcast(base, _) => {
 372                 // Interior or owned data is unique if base is
 373                 // unique.
 374                 self.adjust_upvar_borrow_kind_for_unique(base);
 375             }
 376
 377             Categorization::Deref(base, _, mc::BorrowedPtr(..)) |
 378             Categorization::Deref(base, _, mc::Implicit(..)) => {
 379                 if !self.try_adjust_upvar_deref(&cmt.note, ty::UniqueImmBorrow) {
 380                     // for a borrowed pointer to be unique, its
 381                     // base must be unique
 382                     self.adjust_upvar_borrow_kind_for_unique(base);
 383                 }
 384             }
 385
 386             Categorization::Deref(_, _, mc::UnsafePtr(..)) |
 387             Categorization::StaticItem |
 388             Categorization::Rvalue(_) |
 389             Categorization::Local(_) |
 390             Categorization::Upvar(..) => {
 391             }
 392         }
 393     }
 394
 395     fn try_adjust_upvar_deref(&self,
 396                               note: &mc::Note,
 397                               borrow_kind: ty::BorrowKind)
 398                               -> bool
 399     {
 400         assert!(match borrow_kind {
 401             ty::MutBorrow => true,
 402             ty::UniqueImmBorrow => true,
 403
 404             // imm borrows never require adjusting any kinds, so we don't wind up here
 405             ty::ImmBorrow => false,
 406         });
 407
 408         match *note {
 409             mc::NoteUpvarRef(upvar_id) => {
 410                 // if this is an implicit deref of an
 411                 // upvar, then we need to modify the
 412                 // borrow_kind of the upvar to make sure it
 413                 // is inferred to mutable if necessary
 414                 {
 415                     let upvar_capture_map = &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
 416                     let ub = upvar_capture_map.get_mut(&upvar_id).unwrap();
 417                     self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
 418                 }
 419
 420                 // also need to be in an FnMut closure since this is not an ImmBorrow
 421                 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
 422
 423                 true
 424             }
 425             mc::NoteClosureEnv(upvar_id) => {
 426                 // this kind of deref occurs in a `move` closure, or
 427                 // for a by-value upvar; in either case, to mutate an
 428                 // upvar, we need to be an FnMut closure
 429                 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
 430
 431                 true
 432             }
 433             mc::NoteNone => {
 434                 false
 435             }
 436         }
 437     }
 438
 439     /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
 440     /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
 441     /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
 442     /// some particular use.
 443     fn adjust_upvar_borrow_kind(&self,
 444                                 upvar_id: ty::UpvarId,
 445                                 upvar_capture: &mut ty::UpvarCapture,
 446                                 kind: ty::BorrowKind) {
 447         debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
 448                upvar_id, upvar_capture, kind);
 449
 450         match *upvar_capture {
 451             ty::UpvarCapture::ByValue => {
 452                 // Upvar is already by-value, the strongest criteria.
 453             }
 454             ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
 455                 match (upvar_borrow.kind, kind) {
 456                     // Take RHS:
 457                     (ty::ImmBorrow, ty::UniqueImmBorrow) |
 458                     (ty::ImmBorrow, ty::MutBorrow) |
 459                     (ty::UniqueImmBorrow, ty::MutBorrow) => {
 460                         upvar_borrow.kind = kind;
 461                     }
 462                     // Take LHS:
 463                     (ty::ImmBorrow, ty::ImmBorrow) |
 464                     (ty::UniqueImmBorrow, ty::ImmBorrow) |
 465                     (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
 466                     (ty::MutBorrow, _) => {
 467                     }
 468                 }
 469             }
 470         }
 471     }
 472
 473     fn adjust_closure_kind(&self,
 474                            closure_id: ast::NodeId,
 475                            new_kind: ty::ClosureKind) {
 476         debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
 477                closure_id, new_kind);
 478
 479         if !self.closures_with_inferred_kinds.contains(&closure_id) {
 480             return;
 481         }
 482
 483         let closure_def_id = self.fcx.tcx().map.local_def_id(closure_id);
 484         let closure_kinds = &mut self.fcx.inh.tables.borrow_mut().closure_kinds;
 485         let existing_kind = *closure_kinds.get(&closure_def_id).unwrap();
 486
 487         debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
 488                closure_id, existing_kind, new_kind);
 489
 490         match (existing_kind, new_kind) {
 491             (ty::FnClosureKind, ty::FnClosureKind) |
 492             (ty::FnMutClosureKind, ty::FnClosureKind) |
 493             (ty::FnMutClosureKind, ty::FnMutClosureKind) |
 494             (ty::FnOnceClosureKind, _) => {
 495                 // no change needed
 496             }
 497
 498             (ty::FnClosureKind, ty::FnMutClosureKind) |
 499             (ty::FnClosureKind, ty::FnOnceClosureKind) |
 500             (ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
 501                 // new kind is stronger than the old kind
 502                 closure_kinds.insert(closure_def_id, new_kind);
 503             }
 504         }
 505     }
 506 }
 507
 508 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
 509     fn visit_fn(&mut self,
 510                 fn_kind: intravisit::FnKind<'v>,
 511                 decl: &'v hir::FnDecl,
 512                 body: &'v hir::Block,
 513                 span: Span,
 514                 id: ast::NodeId)
 515     {
 516         intravisit::walk_fn(self, fn_kind, decl, body, span);
 517         self.analyze_closure(id, span, decl, body);
 518     }
 519 }
 520
 521 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
 522     fn consume(&mut self,
 523                _consume_id: ast::NodeId,
 524                _consume_span: Span,
 525                cmt: mc::cmt<'tcx>,
 526                mode: euv::ConsumeMode)
 527     {
 528         debug!("consume(cmt={:?},mode={:?})", cmt, mode);
 529         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 530     }
 531
 532     fn matched_pat(&mut self,
 533                    _matched_pat: &hir::Pat,
 534                    _cmt: mc::cmt<'tcx>,
 535                    _mode: euv::MatchMode)
 536     {}
 537
 538     fn consume_pat(&mut self,
 539                    _consume_pat: &hir::Pat,
 540                    cmt: mc::cmt<'tcx>,
 541                    mode: euv::ConsumeMode)
 542     {
 543         debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
 544         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 545     }
 546
 547     fn borrow(&mut self,
 548               borrow_id: ast::NodeId,
 549               _borrow_span: Span,
 550               cmt: mc::cmt<'tcx>,
 551               _loan_region: ty::Region,
 552               bk: ty::BorrowKind,
 553               _loan_cause: euv::LoanCause)
 554     {
 555         debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
 556                borrow_id, cmt, bk);
 557
 558         match bk {
 559             ty::ImmBorrow => { }
 560             ty::UniqueImmBorrow => {
 561                 self.adjust_upvar_borrow_kind_for_unique(cmt);
 562             }
 563             ty::MutBorrow => {
 564                 self.adjust_upvar_borrow_kind_for_mut(cmt);
 565             }
 566         }
 567     }
 568
 569     fn decl_without_init(&mut self,
 570                          _id: ast::NodeId,
 571                          _span: Span)
 572     {}
 573
 574     fn mutate(&mut self,
 575               _assignment_id: ast::NodeId,
 576               _assignment_span: Span,
 577               assignee_cmt: mc::cmt<'tcx>,
 578               _mode: euv::MutateMode)
 579     {
 580         debug!("mutate(assignee_cmt={:?})",
 581                assignee_cmt);
 582
 583         self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);
 584     }
 585 }