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::visit::{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         visit::walk_expr(self, expr);
 109     }
 110
 111     // Skip all items; they aren't in the same context.
 112     fn visit_item(&mut self, _: &'v hir::Item) { }
 113 }
 114
 115 impl<'a,'tcx> SeedBorrowKind<'a,'tcx> {
 116     fn new(fcx: &'a FnCtxt<'a,'tcx>) -> SeedBorrowKind<'a,'tcx> {
 117         SeedBorrowKind { fcx: fcx, closures_with_inferred_kinds: HashSet::new() }
 118     }
 119
 120     fn tcx(&self) -> &'a ty::ctxt<'tcx> {
 121         self.fcx.tcx()
 122     }
 123
 124     fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
 125         self.fcx.infcx()
 126     }
 127
 128     fn check_closure(&mut self,
 129                      expr: &hir::Expr,
 130                      capture_clause: hir::CaptureClause,
 131                      _body: &hir::Block)
 132     {
 133         let closure_def_id = self.tcx().map.local_def_id(expr.id);
 134         if !self.fcx.inh.tables.borrow().closure_kinds.contains_key(&closure_def_id) {
 135             self.closures_with_inferred_kinds.insert(expr.id);
 136             self.fcx.inh.tables.borrow_mut().closure_kinds
 137                                             .insert(closure_def_id, ty::FnClosureKind);
 138             debug!("check_closure: adding closure_id={:?} to closures_with_inferred_kinds",
 139                    closure_def_id);
 140         }
 141
 142         self.tcx().with_freevars(expr.id, |freevars| {
 143             for freevar in freevars {
 144                 let var_node_id = freevar.def.var_id();
 145                 let upvar_id = ty::UpvarId { var_id: var_node_id,
 146                                              closure_expr_id: expr.id };
 147                 debug!("seed upvar_id {:?}", upvar_id);
 148
 149                 let capture_kind = match capture_clause {
 150                     hir::CaptureByValue => {
 151                         ty::UpvarCapture::ByValue
 152                     }
 153                     hir::CaptureByRef => {
 154                         let origin = UpvarRegion(upvar_id, expr.span);
 155                         let freevar_region = self.infcx().next_region_var(origin);
 156                         let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
 157                                                              region: freevar_region };
 158                         ty::UpvarCapture::ByRef(upvar_borrow)
 159                     }
 160                 };
 161
 162                 self.fcx.inh.tables.borrow_mut().upvar_capture_map.insert(upvar_id, capture_kind);
 163             }
 164         });
 165     }
 166 }
 167
 168 ///////////////////////////////////////////////////////////////////////////
 169 // ADJUST BORROW KIND
 170
 171 struct AdjustBorrowKind<'a,'tcx:'a> {
 172     fcx: &'a FnCtxt<'a,'tcx>,
 173     closures_with_inferred_kinds: &'a HashSet<ast::NodeId>,
 174 }
 175
 176 impl<'a,'tcx> AdjustBorrowKind<'a,'tcx> {
 177     fn new(fcx: &'a FnCtxt<'a,'tcx>,
 178            closures_with_inferred_kinds: &'a HashSet<ast::NodeId>)
 179            -> AdjustBorrowKind<'a,'tcx> {
 180         AdjustBorrowKind { fcx: fcx, closures_with_inferred_kinds: closures_with_inferred_kinds }
 181     }
 182
 183     fn analyze_closure(&mut self,
 184                        id: ast::NodeId,
 185                        span: Span,
 186                        decl: &hir::FnDecl,
 187                        body: &hir::Block) {
 188         /*!
 189          * Analysis starting point.
 190          */
 191
 192         debug!("analyze_closure(id={:?}, body.id={:?})", id, body.id);
 193
 194         {
 195             let mut euv = euv::ExprUseVisitor::new(self, self.fcx.infcx());
 196             euv.walk_fn(decl, body);
 197         }
 198
 199         // Now that we've analyzed the closure, we know how each
 200         // variable is borrowed, and we know what traits the closure
 201         // implements (Fn vs FnMut etc). We now have some updates to do
 202         // with that information.
 203         //
 204         // Note that no closure type C may have an upvar of type C
 205         // (though it may reference itself via a trait object). This
 206         // results from the desugaring of closures to a struct like
 207         // `Foo<..., UV0...UVn>`. If one of those upvars referenced
 208         // C, then the type would have infinite size (and the
 209         // inference algorithm will reject it).
 210
 211         // Extract the type variables UV0...UVn.
 212         let closure_substs = match self.fcx.node_ty(id).sty {
 213             ty::TyClosure(_, ref substs) => substs,
 214             ref t => {
 215                 self.fcx.tcx().sess.span_bug(
 216                     span,
 217                     &format!("type of closure expr {:?} is not a closure {:?}",
 218                              id, t));
 219             }
 220         };
 221
 222         // Equate the type variables with the actual types.
 223         let final_upvar_tys = self.final_upvar_tys(id);
 224         debug!("analyze_closure: id={:?} closure_substs={:?} final_upvar_tys={:?}",
 225                id, closure_substs, final_upvar_tys);
 226         for (&upvar_ty, final_upvar_ty) in closure_substs.upvar_tys.iter().zip(final_upvar_tys) {
 227             demand::eqtype(self.fcx, span, final_upvar_ty, upvar_ty);
 228         }
 229
 230         // Now we must process and remove any deferred resolutions,
 231         // since we have a concrete closure kind.
 232         let closure_def_id = self.fcx.tcx().map.local_def_id(id);
 233         if self.closures_with_inferred_kinds.contains(&id) {
 234             let mut deferred_call_resolutions =
 235                 self.fcx.remove_deferred_call_resolutions(closure_def_id);
 236             for deferred_call_resolution in &mut deferred_call_resolutions {
 237                 deferred_call_resolution.resolve(self.fcx);
 238             }
 239         }
 240     }
 241
 242     // Returns a list of `ClosureUpvar`s for each upvar.
 243     fn final_upvar_tys(&mut self, closure_id: ast::NodeId) -> Vec<Ty<'tcx>> {
 244         // Presently an unboxed closure type cannot "escape" out of a
 245         // function, so we will only encounter ones that originated in the
 246         // local crate or were inlined into it along with some function.
 247         // This may change if abstract return types of some sort are
 248         // implemented.
 249         let tcx = self.fcx.tcx();
 250         tcx.with_freevars(closure_id, |freevars| {
 251             freevars.iter()
 252                     .map(|freevar| {
 253                         let freevar_node_id = freevar.def.var_id();
 254                         let freevar_ty = self.fcx.node_ty(freevar_node_id);
 255                         let upvar_id = ty::UpvarId {
 256                             var_id: freevar_node_id,
 257                             closure_expr_id: closure_id
 258                         };
 259                         let capture = self.fcx.infcx().upvar_capture(upvar_id).unwrap();
 260
 261                         debug!("freevar_node_id={:?} freevar_ty={:?} capture={:?}",
 262                                freevar_node_id, freevar_ty, capture);
 263
 264                         match capture {
 265                             ty::UpvarCapture::ByValue => freevar_ty,
 266                             ty::UpvarCapture::ByRef(borrow) =>
 267                                 tcx.mk_ref(tcx.mk_region(borrow.region),
 268                                            ty::TypeAndMut {
 269                                                ty: freevar_ty,
 270                                                mutbl: borrow.kind.to_mutbl_lossy(),
 271                                            }),
 272                         }
 273                     })
 274                     .collect()
 275             })
 276     }
 277
 278     fn adjust_upvar_borrow_kind_for_consume(&self,
 279                                             cmt: mc::cmt<'tcx>,
 280                                             mode: euv::ConsumeMode)
 281     {
 282         debug!("adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
 283                cmt, mode);
 284
 285         // we only care about moves
 286         match mode {
 287             euv::Copy => { return; }
 288             euv::Move(_) => { }
 289         }
 290
 291         // watch out for a move of the deref of a borrowed pointer;
 292         // for that to be legal, the upvar would have to be borrowed
 293         // by value instead
 294         let guarantor = cmt.guarantor();
 295         debug!("adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
 296                guarantor);
 297         match guarantor.cat {
 298             Categorization::Deref(_, _, mc::BorrowedPtr(..)) |
 299             Categorization::Deref(_, _, mc::Implicit(..)) => {
 300                 match cmt.note {
 301                     mc::NoteUpvarRef(upvar_id) => {
 302                         debug!("adjust_upvar_borrow_kind_for_consume: \
 303                                 setting upvar_id={:?} to by value",
 304                                upvar_id);
 305
 306                         // to move out of an upvar, this must be a FnOnce closure
 307                         self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
 308
 309                         let upvar_capture_map =
 310                             &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
 311                         upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
 312                     }
 313                     mc::NoteClosureEnv(upvar_id) => {
 314                         // we get just a closureenv ref if this is a
 315                         // `move` closure, or if the upvar has already
 316                         // been inferred to by-value. In any case, we
 317                         // must still adjust the kind of the closure
 318                         // to be a FnOnce closure to permit moves out
 319                         // of the environment.
 320                         self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
 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.note, 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(&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.note, 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(&self,
 399                               note: &mc::Note,
 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         match *note {
 412             mc::NoteUpvarRef(upvar_id) => {
 413                 // if this is an implicit deref of an
 414                 // upvar, then we need to modify the
 415                 // borrow_kind of the upvar to make sure it
 416                 // is inferred to mutable if necessary
 417                 {
 418                     let upvar_capture_map = &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
 419                     let ub = upvar_capture_map.get_mut(&upvar_id).unwrap();
 420                     self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
 421                 }
 422
 423                 // also need to be in an FnMut closure since this is not an ImmBorrow
 424                 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
 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, ty::FnMutClosureKind);
 433
 434                 true
 435             }
 436             mc::NoteNone => {
 437                 false
 438             }
 439         }
 440     }
 441
 442     /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
 443     /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
 444     /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
 445     /// some particular use.
 446     fn adjust_upvar_borrow_kind(&self,
 447                                 upvar_id: ty::UpvarId,
 448                                 upvar_capture: &mut ty::UpvarCapture,
 449                                 kind: ty::BorrowKind) {
 450         debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
 451                upvar_id, upvar_capture, kind);
 452
 453         match *upvar_capture {
 454             ty::UpvarCapture::ByValue => {
 455                 // Upvar is already by-value, the strongest criteria.
 456             }
 457             ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
 458                 match (upvar_borrow.kind, kind) {
 459                     // Take RHS:
 460                     (ty::ImmBorrow, ty::UniqueImmBorrow) |
 461                     (ty::ImmBorrow, ty::MutBorrow) |
 462                     (ty::UniqueImmBorrow, ty::MutBorrow) => {
 463                         upvar_borrow.kind = kind;
 464                     }
 465                     // Take LHS:
 466                     (ty::ImmBorrow, ty::ImmBorrow) |
 467                     (ty::UniqueImmBorrow, ty::ImmBorrow) |
 468                     (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
 469                     (ty::MutBorrow, _) => {
 470                     }
 471                 }
 472             }
 473         }
 474     }
 475
 476     fn adjust_closure_kind(&self,
 477                            closure_id: ast::NodeId,
 478                            new_kind: ty::ClosureKind) {
 479         debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
 480                closure_id, new_kind);
 481
 482         if !self.closures_with_inferred_kinds.contains(&closure_id) {
 483             return;
 484         }
 485
 486         let closure_def_id = self.fcx.tcx().map.local_def_id(closure_id);
 487         let closure_kinds = &mut self.fcx.inh.tables.borrow_mut().closure_kinds;
 488         let existing_kind = *closure_kinds.get(&closure_def_id).unwrap();
 489
 490         debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
 491                closure_id, existing_kind, new_kind);
 492
 493         match (existing_kind, new_kind) {
 494             (ty::FnClosureKind, ty::FnClosureKind) |
 495             (ty::FnMutClosureKind, ty::FnClosureKind) |
 496             (ty::FnMutClosureKind, ty::FnMutClosureKind) |
 497             (ty::FnOnceClosureKind, _) => {
 498                 // no change needed
 499             }
 500
 501             (ty::FnClosureKind, ty::FnMutClosureKind) |
 502             (ty::FnClosureKind, ty::FnOnceClosureKind) |
 503             (ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
 504                 // new kind is stronger than the old kind
 505                 closure_kinds.insert(closure_def_id, new_kind);
 506             }
 507         }
 508     }
 509 }
 510
 511 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
 512     fn visit_fn(&mut self,
 513                 fn_kind: visit::FnKind<'v>,
 514                 decl: &'v hir::FnDecl,
 515                 body: &'v hir::Block,
 516                 span: Span,
 517                 id: ast::NodeId)
 518     {
 519         visit::walk_fn(self, fn_kind, decl, body, span);
 520         self.analyze_closure(id, span, decl, body);
 521     }
 522
 523     // Skip all items; they aren't in the same context.
 524     fn visit_item(&mut self, _: &'v hir::Item) { }
 525 }
 526
 527 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
 528     fn consume(&mut self,
 529                _consume_id: ast::NodeId,
 530                _consume_span: Span,
 531                cmt: mc::cmt<'tcx>,
 532                mode: euv::ConsumeMode)
 533     {
 534         debug!("consume(cmt={:?},mode={:?})", cmt, mode);
 535         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 536     }
 537
 538     fn matched_pat(&mut self,
 539                    _matched_pat: &hir::Pat,
 540                    _cmt: mc::cmt<'tcx>,
 541                    _mode: euv::MatchMode)
 542     {}
 543
 544     fn consume_pat(&mut self,
 545                    _consume_pat: &hir::Pat,
 546                    cmt: mc::cmt<'tcx>,
 547                    mode: euv::ConsumeMode)
 548     {
 549         debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
 550         self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
 551     }
 552
 553     fn borrow(&mut self,
 554               borrow_id: ast::NodeId,
 555               _borrow_span: Span,
 556               cmt: mc::cmt<'tcx>,
 557               _loan_region: ty::Region,
 558               bk: ty::BorrowKind,
 559               _loan_cause: euv::LoanCause)
 560     {
 561         debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
 562                borrow_id, cmt, bk);
 563
 564         match bk {
 565             ty::ImmBorrow => { }
 566             ty::UniqueImmBorrow => {
 567                 self.adjust_upvar_borrow_kind_for_unique(cmt);
 568             }
 569             ty::MutBorrow => {
 570                 self.adjust_upvar_borrow_kind_for_mut(cmt);
 571             }
 572         }
 573     }
 574
 575     fn decl_without_init(&mut self,
 576                          _id: ast::NodeId,
 577                          _span: Span)
 578     {}
 579
 580     fn mutate(&mut self,
 581               _assignment_id: ast::NodeId,
 582               _assignment_span: Span,
 583               assignee_cmt: mc::cmt<'tcx>,
 584               _mode: euv::MutateMode)
 585     {
 586         debug!("mutate(assignee_cmt={:?})",
 587                assignee_cmt);
 588
 589         self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);
 590     }
 591 }