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