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 middle::expr_use_visitor as euv;
  46 use middle::mem_categorization as mc;
  47 use middle::mem_categorization::Categorization;
  48 use rustc::ty::{self, Ty};
  49 use rustc::infer::UpvarRegion;
  50 use syntax::ast;
  51 use syntax_pos::Span;
  52 use rustc::hir;
  53 use rustc::hir::def_id::DefIndex;
  54 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  55 use rustc::util::nodemap::FxHashMap;
  56
  57 use std::collections::hash_map::Entry;
  58
  59 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  60     pub fn closure_analyze(&self, body: &'gcx hir::Body) {
  61         InferBorrowKindVisitor { fcx: self }.visit_body(body);
  62
  63         // it's our job to process these.
  64         assert!(self.deferred_call_resolutions.borrow().is_empty());
  65     }
  66 }
  67
  68 struct InferBorrowKindVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  69     fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
  70 }
  71
  72 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for InferBorrowKindVisitor<'a, 'gcx, 'tcx> {
  73     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
  74         NestedVisitorMap::None
  75     }
  76
  77     fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
  78         match expr.node {
  79             hir::ExprClosure(cc, _, body_id, _, is_generator) => {
  80                 let body = self.fcx.tcx.hir.body(body_id);
  81                 self.visit_body(body);
  82                 self.fcx.analyze_closure((expr.id, expr.hir_id),
  83                                          expr.span,
  84                                          body,
  85                                          cc,
  86                                          is_generator);
  87             }
  88
  89             _ => { }
  90         }
  91
  92         intravisit::walk_expr(self, expr);
  93     }
  94 }
  95
  96 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  97     fn analyze_closure(&self,
  98                        (closure_node_id, closure_hir_id): (ast::NodeId, hir::HirId),
  99                        span: Span,
 100                        body: &hir::Body,
 101                        capture_clause: hir::CaptureClause,
 102                        gen: bool) {
 103         /*!
 104          * Analysis starting point.
 105          */
 106
 107         debug!("analyze_closure(id={:?}, body.id={:?})", closure_node_id, body.id());
 108
 109         let infer_kind = if gen {
 110             false
 111         } else {
 112             match self.tables
 113                       .borrow_mut()
 114                       .closure_kinds_mut()
 115                       .entry(closure_hir_id) {
 116                 Entry::Occupied(_) => false,
 117                 Entry::Vacant(entry) => {
 118                     debug!("check_closure: adding closure {:?} as Fn", closure_node_id);
 119                     entry.insert((ty::ClosureKind::Fn, None));
 120                     true
 121                 }
 122             }
 123         };
 124
 125         let closure_def_id = self.tcx.hir.local_def_id(closure_node_id);
 126
 127         self.tcx.with_freevars(closure_node_id, |freevars| {
 128             for freevar in freevars {
 129                 let var_def_id = freevar.def.def_id();
 130                 let upvar_id = ty::UpvarId {
 131                     var_id: var_def_id.index,
 132                     closure_expr_id: closure_def_id.index,
 133                 };
 134                 debug!("seed upvar_id {:?}", upvar_id);
 135
 136                 let capture_kind = match capture_clause {
 137                     hir::CaptureByValue => {
 138                         ty::UpvarCapture::ByValue
 139                     }
 140                     hir::CaptureByRef => {
 141                         let origin = UpvarRegion(upvar_id, span);
 142                         let freevar_region = self.next_region_var(origin);
 143                         let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
 144                                                              region: freevar_region };
 145                         ty::UpvarCapture::ByRef(upvar_borrow)
 146                     }
 147                 };
 148
 149                 self.tables.borrow_mut().upvar_capture_map.insert(upvar_id, capture_kind);
 150             }
 151         });
 152
 153         {
 154             let body_owner_def_id = self.tcx.hir.body_owner_def_id(body.id());
 155             let region_scope_tree = &self.tcx.region_scope_tree(body_owner_def_id);
 156             let mut delegate = InferBorrowKind {
 157                 fcx: self,
 158                 adjust_closure_kinds: FxHashMap(),
 159                 adjust_upvar_captures: ty::UpvarCaptureMap::default(),
 160             };
 161             euv::ExprUseVisitor::with_infer(&mut delegate,
 162                                             &self.infcx,
 163                                             self.param_env,
 164                                             region_scope_tree,
 165                                             &self.tables.borrow())
 166                 .consume_body(body);
 167
 168             // Write the adjusted values back into the main tables.
 169             if infer_kind {
 170                 if let Some(kind) = delegate.adjust_closure_kinds
 171                                             .remove(&closure_def_id.index) {
 172                     self.tables
 173                         .borrow_mut()
 174                         .closure_kinds_mut()
 175                         .insert(closure_hir_id, kind);
 176                 }
 177             }
 178             self.tables.borrow_mut().upvar_capture_map.extend(
 179                 delegate.adjust_upvar_captures);
 180         }
 181
 182         // Now that we've analyzed the closure, we know how each
 183         // variable is borrowed, and we know what traits the closure
 184         // implements (Fn vs FnMut etc). We now have some updates to do
 185         // with that information.
 186         //
 187         // Note that no closure type C may have an upvar of type C
 188         // (though it may reference itself via a trait object). This
 189         // results from the desugaring of closures to a struct like
 190         // `Foo<..., UV0...UVn>`. If one of those upvars referenced
 191         // C, then the type would have infinite size (and the
 192         // inference algorithm will reject it).
 193
 194         // Extract the type variables UV0...UVn.
 195         let (def_id, closure_substs) = match self.node_ty(closure_hir_id).sty {
 196             ty::TyClosure(def_id, substs) |
 197             ty::TyGenerator(def_id, substs, _) => (def_id, substs),
 198             ref t => {
 199                 span_bug!(
 200                     span,
 201                     "type of closure expr {:?} is not a closure {:?}",
 202                     closure_node_id, t);
 203             }
 204         };
 205
 206         // Equate the type variables with the actual types.
 207         let final_upvar_tys = self.final_upvar_tys(closure_node_id);
 208         debug!("analyze_closure: id={:?} closure_substs={:?} final_upvar_tys={:?}",
 209                closure_node_id, closure_substs, final_upvar_tys);
 210         for (upvar_ty, final_upvar_ty) in
 211             closure_substs.upvar_tys(def_id, self.tcx).zip(final_upvar_tys)
 212         {
 213             self.demand_eqtype(span, final_upvar_ty, upvar_ty);
 214         }
 215
 216         // If we are also inferred the closure kind here,
 217         // process any deferred resolutions.
 218         if infer_kind {
 219             let deferred_call_resolutions =
 220                 self.remove_deferred_call_resolutions(closure_def_id);
 221             for deferred_call_resolution in deferred_call_resolutions {
 222                 deferred_call_resolution.resolve(self);
 223             }
 224         }
 225     }
 226
 227     // Returns a list of `ClosureUpvar`s for each upvar.
 228     fn final_upvar_tys(&self, closure_id: ast::NodeId) -> Vec<Ty<'tcx>> {
 229         // Presently an unboxed closure type cannot "escape" out of a
 230         // function, so we will only encounter ones that originated in the
 231         // local crate or were inlined into it along with some function.
 232         // This may change if abstract return types of some sort are
 233         // implemented.
 234         let tcx = self.tcx;
 235         let closure_def_index = tcx.hir.local_def_id(closure_id).index;
 236
 237         tcx.with_freevars(closure_id, |freevars| {
 238             freevars.iter().map(|freevar| {
 239                 let var_def_id = freevar.def.def_id();
 240                 let var_node_id = tcx.hir.as_local_node_id(var_def_id).unwrap();
 241                 let freevar_ty = self.node_ty(tcx.hir.node_to_hir_id(var_node_id));
 242                 let upvar_id = ty::UpvarId {
 243                     var_id: var_def_id.index,
 244                     closure_expr_id: closure_def_index,
 245                 };
 246                 let capture = self.tables.borrow().upvar_capture(upvar_id);
 247
 248                 debug!("var_id={:?} freevar_ty={:?} capture={:?}",
 249                        var_node_id, freevar_ty, capture);
 250
 251                 match capture {
 252                     ty::UpvarCapture::ByValue => freevar_ty,
 253                     ty::UpvarCapture::ByRef(borrow) =>
 254                         tcx.mk_ref(borrow.region,
 255                                     ty::TypeAndMut {
 256                                         ty: freevar_ty,
 257                                         mutbl: borrow.kind.to_mutbl_lossy(),
 258                                     }),
 259                 }
 260             }).collect()
 261         })
 262     }
 263 }
 264
 265 struct InferBorrowKind<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 266     fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
 267     adjust_closure_kinds: FxHashMap<DefIndex, (ty::ClosureKind, Option<(Span, ast::Name)>)>,
 268     adjust_upvar_captures: ty::UpvarCaptureMap<'tcx>,
 269 }
 270
 271 impl<'a, 'gcx, 'tcx> InferBorrowKind<'a, 'gcx, 'tcx> {
 272     fn adjust_upvar_borrow_kind_for_consume(&mut self,
 273                                             cmt: mc::cmt<'tcx>,
 274                                             mode: euv::ConsumeMode)
 275     {
 276         debug!("adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
 277                cmt, mode);
 278
 279         // we only care about moves
 280         match mode {
 281             euv::Copy => { return; }
 282             euv::Move(_) => { }
 283         }
 284
 285         let tcx = self.fcx.tcx;
 286
 287         // watch out for a move of the deref of a borrowed pointer;
 288         // for that to be legal, the upvar would have to be borrowed
 289         // by value instead
 290         let guarantor = cmt.guarantor();
 291         debug!("adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
 292                guarantor);
 293         match guarantor.cat {
 294             Categorization::Deref(_, mc::BorrowedPtr(..)) |
 295             Categorization::Deref(_, mc::Implicit(..)) => {
 296                 match cmt.note {
 297                     mc::NoteUpvarRef(upvar_id) => {
 298                         debug!("adjust_upvar_borrow_kind_for_consume: \
 299                                 setting upvar_id={:?} to by value",
 300                                upvar_id);
 301
 302                         // to move out of an upvar, this must be a FnOnce closure
 303                         self.adjust_closure_kind(upvar_id.closure_expr_id,
 304                                                  ty::ClosureKind::FnOnce,
 305                                                  guarantor.span,
 306                                                  var_name(tcx, upvar_id.var_id));
 307
 308                         self.adjust_upvar_captures.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,
 318                                                  ty::ClosureKind::FnOnce,
 319                                                  guarantor.span,
 320                                                  var_name(tcx, upvar_id.var_id));
 321                     }
 322                     mc::NoteNone => {
 323                     }
 324                 }
 325             }
 326             _ => { }
 327         }
 328     }
 329
 330     /// Indicates that `cmt` is being directly mutated (e.g., assigned
 331     /// to). If cmt contains any by-ref upvars, this implies that
 332     /// those upvars must be borrowed using an `&mut` borrow.
 333     fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
 334         debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})",
 335                cmt);
 336
 337         match cmt.cat.clone() {
 338             Categorization::Deref(base, mc::Unique) |
 339             Categorization::Interior(base, _) |
 340             Categorization::Downcast(base, _) => {
 341                 // Interior or owned data is mutable if base is
 342                 // mutable, so iterate to the base.
 343                 self.adjust_upvar_borrow_kind_for_mut(base);
 344             }
 345
 346             Categorization::Deref(base, mc::BorrowedPtr(..)) |
 347             Categorization::Deref(base, mc::Implicit(..)) => {
 348                 if !self.try_adjust_upvar_deref(cmt, ty::MutBorrow) {
 349                     // assignment to deref of an `&mut`
 350                     // borrowed pointer implies that the
 351                     // pointer itself must be unique, but not
 352                     // necessarily *mutable*
 353                     self.adjust_upvar_borrow_kind_for_unique(base);
 354                 }
 355             }
 356
 357             Categorization::Deref(_, mc::UnsafePtr(..)) |
 358             Categorization::StaticItem |
 359             Categorization::Rvalue(..) |
 360             Categorization::Local(_) |
 361             Categorization::Upvar(..) => {
 362                 return;
 363             }
 364         }
 365     }
 366
 367     fn adjust_upvar_borrow_kind_for_unique(&mut self, cmt: mc::cmt<'tcx>) {
 368         debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})",
 369                cmt);
 370
 371         match cmt.cat.clone() {
 372             Categorization::Deref(base, mc::Unique) |
 373             Categorization::Interior(base, _) |
 374             Categorization::Downcast(base, _) => {
 375                 // Interior or owned data is unique if base is
 376                 // unique.
 377                 self.adjust_upvar_borrow_kind_for_unique(base);
 378             }
 379
 380             Categorization::Deref(base, mc::BorrowedPtr(..)) |
 381             Categorization::Deref(base, mc::Implicit(..)) => {
 382                 if !self.try_adjust_upvar_deref(cmt, ty::UniqueImmBorrow) {
 383                     // for a borrowed pointer to be unique, its
 384                     // base must be unique
 385                     self.adjust_upvar_borrow_kind_for_unique(base);
 386                 }
 387             }
 388
 389             Categorization::Deref(_, mc::UnsafePtr(..)) |
 390             Categorization::StaticItem |
 391             Categorization::Rvalue(..) |
 392             Categorization::Local(_) |
 393             Categorization::Upvar(..) => {
 394             }
 395         }
 396     }
 397
 398     fn try_adjust_upvar_deref(&mut self,
 399                               cmt: mc::cmt<'tcx>,
 400                               borrow_kind: ty::BorrowKind)
 401                               -> bool
 402     {
 403         assert!(match borrow_kind {
 404             ty::MutBorrow => true,
 405             ty::UniqueImmBorrow => true,
 406
 407             // imm borrows never require adjusting any kinds, so we don't wind up here
 408             ty::ImmBorrow => false,
 409         });
 410
 411         let tcx = self.fcx.tcx;
 412
 413         match cmt.note {
 414             mc::NoteUpvarRef(upvar_id) => {
 415                 // if this is an implicit deref of an
 416                 // upvar, then we need to modify the
 417                 // borrow_kind of the upvar to make sure it
 418                 // is inferred to mutable if necessary
 419                 self.adjust_upvar_borrow_kind(upvar_id, borrow_kind);
 420
 421                 // also need to be in an FnMut closure since this is not an ImmBorrow
 422                 self.adjust_closure_kind(upvar_id.closure_expr_id,
 423                                          ty::ClosureKind::FnMut,
 424                                          cmt.span,
 425                                          var_name(tcx, upvar_id.var_id));
 426
 427                 true
 428             }
 429             mc::NoteClosureEnv(upvar_id) => {
 430                 // this kind of deref occurs in a `move` closure, or
 431                 // for a by-value upvar; in either case, to mutate an
 432                 // upvar, we need to be an FnMut closure
 433                 self.adjust_closure_kind(upvar_id.closure_expr_id,
 434                                          ty::ClosureKind::FnMut,
 435                                          cmt.span,
 436                                          var_name(tcx, upvar_id.var_id));
 437
 438                 true
 439             }
 440             mc::NoteNone => {
 441                 false
 442             }
 443         }
 444     }
 445
 446     /// We infer the borrow_kind with which to borrow upvars in a stack closure.
 447     /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
 448     /// moving from left to right as needed (but never right to left).
 449     /// Here the argument `mutbl` is the borrow_kind that is required by
 450     /// some particular use.
 451     fn adjust_upvar_borrow_kind(&mut self,
 452                                 upvar_id: ty::UpvarId,
 453                                 kind: ty::BorrowKind) {
 454         let upvar_capture = self.adjust_upvar_captures.get(&upvar_id).cloned()
 455             .unwrap_or_else(|| self.fcx.tables.borrow().upvar_capture(upvar_id));
 456         debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
 457                upvar_id, upvar_capture, kind);
 458
 459         match upvar_capture {
 460             ty::UpvarCapture::ByValue => {
 461                 // Upvar is already by-value, the strongest criteria.
 462             }
 463             ty::UpvarCapture::ByRef(mut upvar_borrow) => {
 464                 match (upvar_borrow.kind, kind) {
 465                     // Take RHS:
 466                     (ty::ImmBorrow, ty::UniqueImmBorrow) |
 467                     (ty::ImmBorrow, ty::MutBorrow) |
 468                     (ty::UniqueImmBorrow, ty::MutBorrow) => {
 469                         upvar_borrow.kind = kind;
 470                         self.adjust_upvar_captures.insert(upvar_id,
 471                             ty::UpvarCapture::ByRef(upvar_borrow));
 472                     }
 473                     // Take LHS:
 474                     (ty::ImmBorrow, ty::ImmBorrow) |
 475                     (ty::UniqueImmBorrow, ty::ImmBorrow) |
 476                     (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
 477                     (ty::MutBorrow, _) => {
 478                     }
 479                 }
 480             }
 481         }
 482     }
 483
 484     fn adjust_closure_kind(&mut self,
 485                            closure_id: DefIndex,
 486                            new_kind: ty::ClosureKind,
 487                            upvar_span: Span,
 488                            var_name: ast::Name) {
 489         debug!("adjust_closure_kind(closure_id={:?}, new_kind={:?}, upvar_span={:?}, var_name={})",
 490                closure_id, new_kind, upvar_span, var_name);
 491
 492         let closure_kind = self.adjust_closure_kinds.get(&closure_id).cloned()
 493             .or_else(|| {
 494                 let closure_id = self.fcx.tcx.hir.def_index_to_hir_id(closure_id);
 495                 self.fcx.tables.borrow().closure_kinds().get(closure_id).cloned()
 496             });
 497
 498         if let Some((existing_kind, _)) = closure_kind {
 499             debug!("adjust_closure_kind: closure_id={:?}, existing_kind={:?}, new_kind={:?}",
 500                    closure_id, existing_kind, new_kind);
 501
 502             match (existing_kind, new_kind) {
 503                 (ty::ClosureKind::Fn, ty::ClosureKind::Fn) |
 504                 (ty::ClosureKind::FnMut, ty::ClosureKind::Fn) |
 505                 (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut) |
 506                 (ty::ClosureKind::FnOnce, _) => {
 507                     // no change needed
 508                 }
 509
 510                 (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) |
 511                 (ty::ClosureKind::Fn, ty::ClosureKind::FnOnce) |
 512                 (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
 513                     // new kind is stronger than the old kind
 514                     self.adjust_closure_kinds.insert(
 515                         closure_id,
 516                         (new_kind, Some((upvar_span, var_name)))
 517                     );
 518                 }
 519             }
 520         }
 521     }
 522 }
 523
 524 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'gcx, 'tcx> {
 525     fn consume(&mut self,
 526                _consume_id: ast::NodeId,
 527                _consume_span: Span,
 528                cmt: mc::cmt<'tcx>,
 529                mode: euv::ConsumeMode)
 530     {
 531         debug!("consume(cmt={:?},mode={:?})", cmt, mode);
 532         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 533     }
 534
 535     fn matched_pat(&mut self,
 536                    _matched_pat: &hir::Pat,
 537                    _cmt: mc::cmt<'tcx>,
 538                    _mode: euv::MatchMode)
 539     {}
 540
 541     fn consume_pat(&mut self,
 542                    _consume_pat: &hir::Pat,
 543                    cmt: mc::cmt<'tcx>,
 544                    mode: euv::ConsumeMode)
 545     {
 546         debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
 547         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 548     }
 549
 550     fn borrow(&mut self,
 551               borrow_id: ast::NodeId,
 552               _borrow_span: Span,
 553               cmt: mc::cmt<'tcx>,
 554               _loan_region: ty::Region<'tcx>,
 555               bk: ty::BorrowKind,
 556               _loan_cause: euv::LoanCause)
 557     {
 558         debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
 559                borrow_id, cmt, bk);
 560
 561         match bk {
 562             ty::ImmBorrow => { }
 563             ty::UniqueImmBorrow => {
 564                 self.adjust_upvar_borrow_kind_for_unique(cmt);
 565             }
 566             ty::MutBorrow => {
 567                 self.adjust_upvar_borrow_kind_for_mut(cmt);
 568             }
 569         }
 570     }
 571
 572     fn decl_without_init(&mut self,
 573                          _id: ast::NodeId,
 574                          _span: Span)
 575     {}
 576
 577     fn mutate(&mut self,
 578               _assignment_id: ast::NodeId,
 579               _assignment_span: Span,
 580               assignee_cmt: mc::cmt<'tcx>,
 581               _mode: euv::MutateMode)
 582     {
 583         debug!("mutate(assignee_cmt={:?})",
 584                assignee_cmt);
 585
 586         self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);
 587     }
 588 }
 589
 590 fn var_name(tcx: ty::TyCtxt, var_def_index: DefIndex) -> ast::Name {
 591     let var_node_id = tcx.hir.def_index_to_node_id(var_def_index);
 592     tcx.hir.name(var_node_id)
 593 }