src/librustc/middle/expr_use_visitor.rs

   1 // Copyright 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 //! A different sort of visitor for walking fn bodies.  Unlike the
  12 //! normal visitor, which just walks the entire body in one shot, the
  13 //! `ExprUseVisitor` determines how expressions are being used.
  14
  15 pub use self::MutateMode::*;
  16 pub use self::LoanCause::*;
  17 pub use self::ConsumeMode::*;
  18 pub use self::MoveReason::*;
  19 pub use self::MatchMode::*;
  20 use self::TrackMatchMode::*;
  21 use self::OverloadedCallType::*;
  22
  23 use middle::{def, region, pat_util};
  24 use middle::mem_categorization as mc;
  25 use middle::mem_categorization::Typer;
  26 use middle::ty::{self};
  27 use middle::ty::{MethodCall, MethodObject, MethodTraitObject};
  28 use middle::ty::{MethodOrigin, MethodParam, MethodTypeParam};
  29 use middle::ty::{MethodStatic, MethodStaticClosure};
  30 use util::ppaux::Repr;
  31
  32 use syntax::{ast, ast_util};
  33 use syntax::ptr::P;
  34 use syntax::codemap::Span;
  35
  36 ///////////////////////////////////////////////////////////////////////////
  37 // The Delegate trait
  38
  39 /// This trait defines the callbacks you can expect to receive when
  40 /// employing the ExprUseVisitor.
  41 pub trait Delegate<'tcx> {
  42     // The value found at `cmt` is either copied or moved, depending
  43     // on mode.
  44     fn consume(&mut self,
  45                consume_id: ast::NodeId,
  46                consume_span: Span,
  47                cmt: mc::cmt<'tcx>,
  48                mode: ConsumeMode);
  49
  50     // The value found at `cmt` has been determined to match the
  51     // pattern binding `matched_pat`, and its subparts are being
  52     // copied or moved depending on `mode`.  Note that `matched_pat`
  53     // is called on all variant/structs in the pattern (i.e., the
  54     // interior nodes of the pattern's tree structure) while
  55     // consume_pat is called on the binding identifiers in the pattern
  56     // (which are leaves of the pattern's tree structure).
  57     //
  58     // Note that variants/structs and identifiers are disjoint; thus
  59     // `matched_pat` and `consume_pat` are never both called on the
  60     // same input pattern structure (though of `consume_pat` can be
  61     // called on a subpart of an input passed to `matched_pat).
  62     fn matched_pat(&mut self,
  63                    matched_pat: &ast::Pat,
  64                    cmt: mc::cmt<'tcx>,
  65                    mode: MatchMode);
  66
  67     // The value found at `cmt` is either copied or moved via the
  68     // pattern binding `consume_pat`, depending on mode.
  69     fn consume_pat(&mut self,
  70                    consume_pat: &ast::Pat,
  71                    cmt: mc::cmt<'tcx>,
  72                    mode: ConsumeMode);
  73
  74     // The value found at `borrow` is being borrowed at the point
  75     // `borrow_id` for the region `loan_region` with kind `bk`.
  76     fn borrow(&mut self,
  77               borrow_id: ast::NodeId,
  78               borrow_span: Span,
  79               cmt: mc::cmt<'tcx>,
  80               loan_region: ty::Region,
  81               bk: ty::BorrowKind,
  82               loan_cause: LoanCause);
  83
  84     // The local variable `id` is declared but not initialized.
  85     fn decl_without_init(&mut self,
  86                          id: ast::NodeId,
  87                          span: Span);
  88
  89     // The path at `cmt` is being assigned to.
  90     fn mutate(&mut self,
  91               assignment_id: ast::NodeId,
  92               assignment_span: Span,
  93               assignee_cmt: mc::cmt<'tcx>,
  94               mode: MutateMode);
  95 }
  96
  97 #[derive(Copy, Clone, PartialEq, Debug)]
  98 pub enum LoanCause {
  99     ClosureCapture(Span),
 100     AddrOf,
 101     AutoRef,
 102     AutoUnsafe,
 103     RefBinding,
 104     OverloadedOperator,
 105     ClosureInvocation,
 106     ForLoop,
 107     MatchDiscriminant
 108 }
 109
 110 #[derive(Copy, Clone, PartialEq, Debug)]
 111 pub enum ConsumeMode {
 112     Copy,                // reference to x where x has a type that copies
 113     Move(MoveReason),    // reference to x where x has a type that moves
 114 }
 115
 116 #[derive(Copy, Clone, PartialEq, Debug)]
 117 pub enum MoveReason {
 118     DirectRefMove,
 119     PatBindingMove,
 120     CaptureMove,
 121 }
 122
 123 #[derive(Copy, Clone, PartialEq, Debug)]
 124 pub enum MatchMode {
 125     NonBindingMatch,
 126     BorrowingMatch,
 127     CopyingMatch,
 128     MovingMatch,
 129 }
 130
 131 #[derive(Copy, Clone, PartialEq, Debug)]
 132 enum TrackMatchMode {
 133     Unknown,
 134     Definite(MatchMode),
 135     Conflicting,
 136 }
 137
 138 impl TrackMatchMode {
 139     // Builds up the whole match mode for a pattern from its constituent
 140     // parts.  The lattice looks like this:
 141     //
 142     //          Conflicting
 143     //            /     \
 144     //           /       \
 145     //      Borrowing   Moving
 146     //           \       /
 147     //            \     /
 148     //            Copying
 149     //               |
 150     //          NonBinding
 151     //               |
 152     //            Unknown
 153     //
 154     // examples:
 155     //
 156     // * `(_, some_int)` pattern is Copying, since
 157     //   NonBinding + Copying => Copying
 158     //
 159     // * `(some_int, some_box)` pattern is Moving, since
 160     //   Copying + Moving => Moving
 161     //
 162     // * `(ref x, some_box)` pattern is Conflicting, since
 163     //   Borrowing + Moving => Conflicting
 164     //
 165     // Note that the `Unknown` and `Conflicting` states are
 166     // represented separately from the other more interesting
 167     // `Definite` states, which simplifies logic here somewhat.
 168     fn lub(&mut self, mode: MatchMode) {
 169         *self = match (*self, mode) {
 170             // Note that clause order below is very significant.
 171             (Unknown, new) => Definite(new),
 172             (Definite(old), new) if old == new => Definite(old),
 173
 174             (Definite(old), NonBindingMatch) => Definite(old),
 175             (Definite(NonBindingMatch), new) => Definite(new),
 176
 177             (Definite(old), CopyingMatch) => Definite(old),
 178             (Definite(CopyingMatch), new) => Definite(new),
 179
 180             (Definite(_), _) => Conflicting,
 181             (Conflicting, _) => *self,
 182         };
 183     }
 184
 185     fn match_mode(&self) -> MatchMode {
 186         match *self {
 187             Unknown => NonBindingMatch,
 188             Definite(mode) => mode,
 189             Conflicting => {
 190                 // Conservatively return MovingMatch to let the
 191                 // compiler continue to make progress.
 192                 MovingMatch
 193             }
 194         }
 195     }
 196 }
 197
 198 #[derive(Copy, Clone, PartialEq, Debug)]
 199 pub enum MutateMode {
 200     Init,
 201     JustWrite,    // x = y
 202     WriteAndRead, // x += y
 203 }
 204
 205 #[derive(Copy, Clone)]
 206 enum OverloadedCallType {
 207     FnOverloadedCall,
 208     FnMutOverloadedCall,
 209     FnOnceOverloadedCall,
 210 }
 211
 212 impl OverloadedCallType {
 213     fn from_trait_id(tcx: &ty::ctxt, trait_id: ast::DefId)
 214                      -> OverloadedCallType {
 215         for &(maybe_function_trait, overloaded_call_type) in [
 216             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 217             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 218             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 219         ].iter() {
 220             match maybe_function_trait {
 221                 Some(function_trait) if function_trait == trait_id => {
 222                     return overloaded_call_type
 223                 }
 224                 _ => continue,
 225             }
 226         }
 227
 228         tcx.sess.bug("overloaded call didn't map to known function trait")
 229     }
 230
 231     fn from_method_id(tcx: &ty::ctxt, method_id: ast::DefId)
 232                       -> OverloadedCallType {
 233         let method_descriptor = match ty::impl_or_trait_item(tcx, method_id) {
 234             ty::MethodTraitItem(ref method_descriptor) => {
 235                 (*method_descriptor).clone()
 236             }
 237             _ => {
 238                 tcx.sess.bug("overloaded call method wasn't in method map")
 239             }
 240         };
 241         let impl_id = match method_descriptor.container {
 242             ty::TraitContainer(_) => {
 243                 tcx.sess.bug("statically resolved overloaded call method \
 244                               belonged to a trait?!")
 245             }
 246             ty::ImplContainer(impl_id) => impl_id,
 247         };
 248         let trait_ref = match ty::impl_trait_ref(tcx, impl_id) {
 249             None => {
 250                 tcx.sess.bug("statically resolved overloaded call impl \
 251                               didn't implement a trait?!")
 252             }
 253             Some(ref trait_ref) => (*trait_ref).clone(),
 254         };
 255         OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 256     }
 257
 258     fn from_closure(tcx: &ty::ctxt, closure_did: ast::DefId)
 259                     -> OverloadedCallType {
 260         let trait_did =
 261             tcx.closure_kinds
 262                .borrow()
 263                .get(&closure_did)
 264                .expect("OverloadedCallType::from_closure: didn't find closure id")
 265                .trait_did(tcx);
 266         OverloadedCallType::from_trait_id(tcx, trait_did)
 267     }
 268
 269     fn from_method_origin(tcx: &ty::ctxt, origin: &MethodOrigin)
 270                           -> OverloadedCallType {
 271         match *origin {
 272             MethodStatic(def_id) => {
 273                 OverloadedCallType::from_method_id(tcx, def_id)
 274             }
 275             MethodStaticClosure(def_id) => {
 276                 OverloadedCallType::from_closure(tcx, def_id)
 277             }
 278             MethodTypeParam(MethodParam { ref trait_ref, .. }) |
 279             MethodTraitObject(MethodObject { ref trait_ref, .. }) => {
 280                 OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 281             }
 282         }
 283     }
 284 }
 285
 286 ///////////////////////////////////////////////////////////////////////////
 287 // The ExprUseVisitor type
 288 //
 289 // This is the code that actually walks the tree. Like
 290 // mem_categorization, it requires a TYPER, which is a type that
 291 // supplies types from the tree. After type checking is complete, you
 292 // can just use the tcx as the typer.
 293
 294 pub struct ExprUseVisitor<'d,'t,'tcx:'t,TYPER:'t> {
 295     typer: &'t TYPER,
 296     mc: mc::MemCategorizationContext<'t,TYPER>,
 297     delegate: &'d mut (Delegate<'tcx>+'d),
 298 }
 299
 300 // If the TYPER results in an error, it's because the type check
 301 // failed (or will fail, when the error is uncovered and reported
 302 // during writeback). In this case, we just ignore this part of the
 303 // code.
 304 //
 305 // Note that this macro appears similar to try!(), but, unlike try!(),
 306 // it does not propagate the error.
 307 macro_rules! return_if_err {
 308     ($inp: expr) => (
 309         match $inp {
 310             Ok(v) => v,
 311             Err(()) => return
 312         }
 313     )
 314 }
 315
 316 /// Whether the elements of an overloaded operation are passed by value or by reference
 317 enum PassArgs {
 318     ByValue,
 319     ByRef,
 320 }
 321
 322 impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
 323     pub fn new(delegate: &'d mut Delegate<'tcx>,
 324                typer: &'t TYPER)
 325                -> ExprUseVisitor<'d,'t,'tcx,TYPER> {
 326         ExprUseVisitor {
 327             typer: typer,
 328             mc: mc::MemCategorizationContext::new(typer),
 329             delegate: delegate,
 330         }
 331     }
 332
 333     pub fn walk_fn(&mut self,
 334                    decl: &ast::FnDecl,
 335                    body: &ast::Block) {
 336         self.walk_arg_patterns(decl, body);
 337         self.walk_block(body);
 338     }
 339
 340     fn walk_arg_patterns(&mut self,
 341                          decl: &ast::FnDecl,
 342                          body: &ast::Block) {
 343         for arg in &decl.inputs {
 344             let arg_ty = return_if_err!(self.typer.node_ty(arg.pat.id));
 345
 346             let fn_body_scope = region::CodeExtent::from_node_id(body.id);
 347             let arg_cmt = self.mc.cat_rvalue(
 348                 arg.id,
 349                 arg.pat.span,
 350                 ty::ReScope(fn_body_scope), // Args live only as long as the fn body.
 351                 arg_ty);
 352
 353             self.walk_irrefutable_pat(arg_cmt, &*arg.pat);
 354         }
 355     }
 356
 357     fn tcx(&self) -> &'t ty::ctxt<'tcx> {
 358         self.typer.tcx()
 359     }
 360
 361     fn delegate_consume(&mut self,
 362                         consume_id: ast::NodeId,
 363                         consume_span: Span,
 364                         cmt: mc::cmt<'tcx>) {
 365         debug!("delegate_consume(consume_id={}, cmt={})",
 366                consume_id, cmt.repr(self.tcx()));
 367
 368         let mode = copy_or_move(self.typer, &cmt, DirectRefMove);
 369         self.delegate.consume(consume_id, consume_span, cmt, mode);
 370     }
 371
 372     fn consume_exprs(&mut self, exprs: &Vec<P<ast::Expr>>) {
 373         for expr in exprs {
 374             self.consume_expr(&**expr);
 375         }
 376     }
 377
 378     pub fn consume_expr(&mut self, expr: &ast::Expr) {
 379         debug!("consume_expr(expr={})", expr.repr(self.tcx()));
 380
 381         let cmt = return_if_err!(self.mc.cat_expr(expr));
 382         self.delegate_consume(expr.id, expr.span, cmt);
 383         self.walk_expr(expr);
 384     }
 385
 386     fn mutate_expr(&mut self,
 387                    assignment_expr: &ast::Expr,
 388                    expr: &ast::Expr,
 389                    mode: MutateMode) {
 390         let cmt = return_if_err!(self.mc.cat_expr(expr));
 391         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 392         self.walk_expr(expr);
 393     }
 394
 395     fn borrow_expr(&mut self,
 396                    expr: &ast::Expr,
 397                    r: ty::Region,
 398                    bk: ty::BorrowKind,
 399                    cause: LoanCause) {
 400         debug!("borrow_expr(expr={}, r={}, bk={})",
 401                expr.repr(self.tcx()), r.repr(self.tcx()), bk.repr(self.tcx()));
 402
 403         let cmt = return_if_err!(self.mc.cat_expr(expr));
 404         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 405
 406         // Note: Unlike consume, we can ignore ExprParen. cat_expr
 407         // already skips over them, and walk will uncover any
 408         // attachments or whatever.
 409         self.walk_expr(expr)
 410     }
 411
 412     fn select_from_expr(&mut self, expr: &ast::Expr) {
 413         self.walk_expr(expr)
 414     }
 415
 416     pub fn walk_expr(&mut self, expr: &ast::Expr) {
 417         debug!("walk_expr(expr={})", expr.repr(self.tcx()));
 418
 419         self.walk_adjustment(expr);
 420
 421         match expr.node {
 422             ast::ExprParen(ref subexpr) => {
 423                 self.walk_expr(&**subexpr)
 424             }
 425
 426             ast::ExprPath(..) => { }
 427
 428             ast::ExprUnary(ast::UnDeref, ref base) => {      // *base
 429                 if !self.walk_overloaded_operator(expr, &**base, Vec::new(), PassArgs::ByRef) {
 430                     self.select_from_expr(&**base);
 431                 }
 432             }
 433
 434             ast::ExprField(ref base, _) => {         // base.f
 435                 self.select_from_expr(&**base);
 436             }
 437
 438             ast::ExprTupField(ref base, _) => {         // base.<n>
 439                 self.select_from_expr(&**base);
 440             }
 441
 442             ast::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 443                 if !self.walk_overloaded_operator(expr,
 444                                                   &**lhs,
 445                                                   vec![&**rhs],
 446                                                   PassArgs::ByValue) {
 447                     self.select_from_expr(&**lhs);
 448                     self.consume_expr(&**rhs);
 449                 }
 450             }
 451
 452             ast::ExprRange(ref start, ref end) => {
 453                 start.as_ref().map(|e| self.consume_expr(&**e));
 454                 end.as_ref().map(|e| self.consume_expr(&**e));
 455             }
 456
 457             ast::ExprCall(ref callee, ref args) => {    // callee(args)
 458                 self.walk_callee(expr, &**callee);
 459                 self.consume_exprs(args);
 460             }
 461
 462             ast::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 463                 self.consume_exprs(args);
 464             }
 465
 466             ast::ExprStruct(_, ref fields, ref opt_with) => {
 467                 self.walk_struct_expr(expr, fields, opt_with);
 468             }
 469
 470             ast::ExprTup(ref exprs) => {
 471                 self.consume_exprs(exprs);
 472             }
 473
 474             ast::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
 475                 self.consume_expr(&**cond_expr);
 476                 self.walk_block(&**then_blk);
 477                 if let Some(ref else_expr) = *opt_else_expr {
 478                     self.consume_expr(&**else_expr);
 479                 }
 480             }
 481
 482             ast::ExprIfLet(..) => {
 483                 self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
 484             }
 485
 486             ast::ExprMatch(ref discr, ref arms, _) => {
 487                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
 488                 self.borrow_expr(&**discr, ty::ReEmpty, ty::ImmBorrow, MatchDiscriminant);
 489
 490                 // treatment of the discriminant is handled while walking the arms.
 491                 for arm in arms {
 492                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 493                     let mode = mode.match_mode();
 494                     self.walk_arm(discr_cmt.clone(), arm, mode);
 495                 }
 496             }
 497
 498             ast::ExprVec(ref exprs) => {
 499                 self.consume_exprs(exprs);
 500             }
 501
 502             ast::ExprAddrOf(m, ref base) => {   // &base
 503                 // make sure that the thing we are pointing out stays valid
 504                 // for the lifetime `scope_r` of the resulting ptr:
 505                 let expr_ty = return_if_err!(self.typer.node_ty(expr.id));
 506                 let r = ty::ty_region(self.tcx(), expr.span, expr_ty);
 507                 let bk = ty::BorrowKind::from_mutbl(m);
 508                 self.borrow_expr(&**base, r, bk, AddrOf);
 509             }
 510
 511             ast::ExprInlineAsm(ref ia) => {
 512                 for &(_, ref input) in &ia.inputs {
 513                     self.consume_expr(&**input);
 514                 }
 515
 516                 for &(_, ref output, is_rw) in &ia.outputs {
 517                     self.mutate_expr(expr, &**output,
 518                                            if is_rw { WriteAndRead } else { JustWrite });
 519                 }
 520             }
 521
 522             ast::ExprBreak(..) |
 523             ast::ExprAgain(..) |
 524             ast::ExprLit(..) => {}
 525
 526             ast::ExprLoop(ref blk, _) => {
 527                 self.walk_block(&**blk);
 528             }
 529
 530             ast::ExprWhile(ref cond_expr, ref blk, _) => {
 531                 self.consume_expr(&**cond_expr);
 532                 self.walk_block(&**blk);
 533             }
 534
 535             ast::ExprWhileLet(..) => {
 536                 self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet");
 537             }
 538
 539             ast::ExprForLoop(..) => {
 540                 self.tcx().sess.span_bug(expr.span, "non-desugared ExprForLoop");
 541             }
 542
 543             ast::ExprUnary(op, ref lhs) => {
 544                 let pass_args = if ast_util::is_by_value_unop(op) {
 545                     PassArgs::ByValue
 546                 } else {
 547                     PassArgs::ByRef
 548                 };
 549
 550                 if !self.walk_overloaded_operator(expr, &**lhs, Vec::new(), pass_args) {
 551                     self.consume_expr(&**lhs);
 552                 }
 553             }
 554
 555             ast::ExprBinary(op, ref lhs, ref rhs) => {
 556                 let pass_args = if ast_util::is_by_value_binop(op.node) {
 557                     PassArgs::ByValue
 558                 } else {
 559                     PassArgs::ByRef
 560                 };
 561
 562                 if !self.walk_overloaded_operator(expr, &**lhs, vec![&**rhs], pass_args) {
 563                     self.consume_expr(&**lhs);
 564                     self.consume_expr(&**rhs);
 565                 }
 566             }
 567
 568             ast::ExprBlock(ref blk) => {
 569                 self.walk_block(&**blk);
 570             }
 571
 572             ast::ExprRet(ref opt_expr) => {
 573                 if let Some(ref expr) = *opt_expr {
 574                     self.consume_expr(&**expr);
 575                 }
 576             }
 577
 578             ast::ExprAssign(ref lhs, ref rhs) => {
 579                 self.mutate_expr(expr, &**lhs, JustWrite);
 580                 self.consume_expr(&**rhs);
 581             }
 582
 583             ast::ExprCast(ref base, _) => {
 584                 self.consume_expr(&**base);
 585             }
 586
 587             ast::ExprAssignOp(_, ref lhs, ref rhs) => {
 588                 // This will have to change if/when we support
 589                 // overloaded operators for `+=` and so forth.
 590                 self.mutate_expr(expr, &**lhs, WriteAndRead);
 591                 self.consume_expr(&**rhs);
 592             }
 593
 594             ast::ExprRepeat(ref base, ref count) => {
 595                 self.consume_expr(&**base);
 596                 self.consume_expr(&**count);
 597             }
 598
 599             ast::ExprClosure(..) => {
 600                 self.walk_captures(expr)
 601             }
 602
 603             ast::ExprBox(ref place, ref base) => {
 604                 match *place {
 605                     Some(ref place) => self.consume_expr(&**place),
 606                     None => {}
 607                 }
 608                 self.consume_expr(&**base);
 609             }
 610
 611             ast::ExprMac(..) => {
 612                 self.tcx().sess.span_bug(
 613                     expr.span,
 614                     "macro expression remains after expansion");
 615             }
 616         }
 617     }
 618
 619     fn walk_callee(&mut self, call: &ast::Expr, callee: &ast::Expr) {
 620         let callee_ty = return_if_err!(self.typer.expr_ty_adjusted(callee));
 621         debug!("walk_callee: callee={} callee_ty={}",
 622                callee.repr(self.tcx()), callee_ty.repr(self.tcx()));
 623         let call_scope = region::CodeExtent::from_node_id(call.id);
 624         match callee_ty.sty {
 625             ty::ty_bare_fn(..) => {
 626                 self.consume_expr(callee);
 627             }
 628             ty::ty_err => { }
 629             _ => {
 630                 let overloaded_call_type =
 631                     match self.typer.node_method_origin(MethodCall::expr(call.id)) {
 632                         Some(method_origin) => {
 633                             OverloadedCallType::from_method_origin(
 634                                 self.tcx(),
 635                                 &method_origin)
 636                         }
 637                         None => {
 638                             self.tcx().sess.span_bug(
 639                                 callee.span,
 640                                 &format!("unexpected callee type {}", callee_ty.repr(self.tcx())))
 641                         }
 642                     };
 643                 match overloaded_call_type {
 644                     FnMutOverloadedCall => {
 645                         self.borrow_expr(callee,
 646                                          ty::ReScope(call_scope),
 647                                          ty::MutBorrow,
 648                                          ClosureInvocation);
 649                     }
 650                     FnOverloadedCall => {
 651                         self.borrow_expr(callee,
 652                                          ty::ReScope(call_scope),
 653                                          ty::ImmBorrow,
 654                                          ClosureInvocation);
 655                     }
 656                     FnOnceOverloadedCall => self.consume_expr(callee),
 657                 }
 658             }
 659         }
 660     }
 661
 662     fn walk_stmt(&mut self, stmt: &ast::Stmt) {
 663         match stmt.node {
 664             ast::StmtDecl(ref decl, _) => {
 665                 match decl.node {
 666                     ast::DeclLocal(ref local) => {
 667                         self.walk_local(&**local);
 668                     }
 669
 670                     ast::DeclItem(_) => {
 671                         // we don't visit nested items in this visitor,
 672                         // only the fn body we were given.
 673                     }
 674                 }
 675             }
 676
 677             ast::StmtExpr(ref expr, _) |
 678             ast::StmtSemi(ref expr, _) => {
 679                 self.consume_expr(&**expr);
 680             }
 681
 682             ast::StmtMac(..) => {
 683                 self.tcx().sess.span_bug(stmt.span, "unexpanded stmt macro");
 684             }
 685         }
 686     }
 687
 688     fn walk_local(&mut self, local: &ast::Local) {
 689         match local.init {
 690             None => {
 691                 let delegate = &mut self.delegate;
 692                 pat_util::pat_bindings(&self.typer.tcx().def_map, &*local.pat,
 693                                        |_, id, span, _| {
 694                     delegate.decl_without_init(id, span);
 695                 })
 696             }
 697
 698             Some(ref expr) => {
 699                 // Variable declarations with
 700                 // initializers are considered
 701                 // "assigns", which is handled by
 702                 // `walk_pat`:
 703                 self.walk_expr(&**expr);
 704                 let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
 705                 self.walk_irrefutable_pat(init_cmt, &*local.pat);
 706             }
 707         }
 708     }
 709
 710     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 711     /// depending on its type.
 712     fn walk_block(&mut self, blk: &ast::Block) {
 713         debug!("walk_block(blk.id={})", blk.id);
 714
 715         for stmt in &blk.stmts {
 716             self.walk_stmt(&**stmt);
 717         }
 718
 719         if let Some(ref tail_expr) = blk.expr {
 720             self.consume_expr(&**tail_expr);
 721         }
 722     }
 723
 724     fn walk_struct_expr(&mut self,
 725                         _expr: &ast::Expr,
 726                         fields: &Vec<ast::Field>,
 727                         opt_with: &Option<P<ast::Expr>>) {
 728         // Consume the expressions supplying values for each field.
 729         for field in fields {
 730             self.consume_expr(&*field.expr);
 731         }
 732
 733         let with_expr = match *opt_with {
 734             Some(ref w) => &**w,
 735             None => { return; }
 736         };
 737
 738         let with_cmt = return_if_err!(self.mc.cat_expr(&*with_expr));
 739
 740         // Select just those fields of the `with`
 741         // expression that will actually be used
 742         let with_fields = match with_cmt.ty.sty {
 743             ty::ty_struct(did, substs) => {
 744                 ty::struct_fields(self.tcx(), did, substs)
 745             }
 746             _ => {
 747                 // the base expression should always evaluate to a
 748                 // struct; however, when EUV is run during typeck, it
 749                 // may not. This will generate an error earlier in typeck,
 750                 // so we can just ignore it.
 751                 if !self.tcx().sess.has_errors() {
 752                     self.tcx().sess.span_bug(
 753                         with_expr.span,
 754                         "with expression doesn't evaluate to a struct");
 755                 }
 756                 assert!(self.tcx().sess.has_errors());
 757                 vec!()
 758             }
 759         };
 760
 761         // Consume those fields of the with expression that are needed.
 762         for with_field in &with_fields {
 763             if !contains_field_named(with_field, fields) {
 764                 let cmt_field = self.mc.cat_field(&*with_expr,
 765                                                   with_cmt.clone(),
 766                                                   with_field.name,
 767                                                   with_field.mt.ty);
 768                 self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 769             }
 770         }
 771
 772         // walk the with expression so that complex expressions
 773         // are properly handled.
 774         self.walk_expr(with_expr);
 775
 776         fn contains_field_named(field: &ty::field,
 777                                 fields: &Vec<ast::Field>)
 778                                 -> bool
 779         {
 780             fields.iter().any(
 781                 |f| f.ident.node.name == field.name)
 782         }
 783     }
 784
 785     // Invoke the appropriate delegate calls for anything that gets
 786     // consumed or borrowed as part of the automatic adjustment
 787     // process.
 788     fn walk_adjustment(&mut self, expr: &ast::Expr) {
 789         let typer = self.typer;
 790         if let Some(adjustment) = typer.adjustments().borrow().get(&expr.id) {
 791             match *adjustment {
 792                 ty::AdjustReifyFnPointer |
 793                 ty::AdjustUnsafeFnPointer => {
 794                     // Creating a closure/fn-pointer or unsizing consumes
 795                     // the input and stores it into the resulting rvalue.
 796                     debug!("walk_adjustment(AdjustReifyFnPointer|AdjustUnsafeFnPointer)");
 797                     let cmt_unadjusted =
 798                         return_if_err!(self.mc.cat_expr_unadjusted(expr));
 799                     self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 800                 }
 801                 ty::AdjustDerefRef(ref adj) => {
 802                     self.walk_autoderefref(expr, adj);
 803                 }
 804             }
 805         }
 806     }
 807
 808     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 809     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 810     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 811     fn walk_autoderefs(&mut self,
 812                        expr: &ast::Expr,
 813                        autoderefs: usize) {
 814         debug!("walk_autoderefs expr={} autoderefs={}", expr.repr(self.tcx()), autoderefs);
 815
 816         for i in 0..autoderefs {
 817             let deref_id = ty::MethodCall::autoderef(expr.id, i as u32);
 818             match self.typer.node_method_ty(deref_id) {
 819                 None => {}
 820                 Some(method_ty) => {
 821                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 822
 823                     // the method call infrastructure should have
 824                     // replaced all late-bound regions with variables:
 825                     let self_ty = ty::ty_fn_sig(method_ty).input(0);
 826                     let self_ty = ty::no_late_bound_regions(self.tcx(), &self_ty).unwrap();
 827
 828                     let (m, r) = match self_ty.sty {
 829                         ty::ty_rptr(r, ref m) => (m.mutbl, r),
 830                         _ => self.tcx().sess.span_bug(expr.span,
 831                                 &format!("bad overloaded deref type {}",
 832                                     method_ty.repr(self.tcx())))
 833                     };
 834                     let bk = ty::BorrowKind::from_mutbl(m);
 835                     self.delegate.borrow(expr.id, expr.span, cmt,
 836                                          *r, bk, AutoRef);
 837                 }
 838             }
 839         }
 840     }
 841
 842     fn walk_autoderefref(&mut self,
 843                          expr: &ast::Expr,
 844                          adj: &ty::AutoDerefRef<'tcx>) {
 845         debug!("walk_autoderefref expr={} adj={}",
 846                expr.repr(self.tcx()),
 847                adj.repr(self.tcx()));
 848
 849         self.walk_autoderefs(expr, adj.autoderefs);
 850
 851         let cmt_derefd =
 852             return_if_err!(self.mc.cat_expr_autoderefd(expr, adj.autoderefs));
 853
 854         let cmt_refd =
 855             self.walk_autoref(expr, cmt_derefd, adj.autoref);
 856
 857         if adj.unsize.is_some() {
 858             // Unsizing consumes the thin pointer and produces a fat one.
 859             self.delegate_consume(expr.id, expr.span, cmt_refd);
 860         }
 861     }
 862
 863
 864     /// Walks the autoref `opt_autoref` applied to the autoderef'd
 865     /// `expr`. `cmt_derefd` is the mem-categorized form of `expr`
 866     /// after all relevant autoderefs have occurred. Because AutoRefs
 867     /// can be recursive, this function is recursive: it first walks
 868     /// deeply all the way down the autoref chain, and then processes
 869     /// the autorefs on the way out. At each point, it returns the
 870     /// `cmt` for the rvalue that will be produced by introduced an
 871     /// autoref.
 872     fn walk_autoref(&mut self,
 873                     expr: &ast::Expr,
 874                     cmt_base: mc::cmt<'tcx>,
 875                     opt_autoref: Option<ty::AutoRef<'tcx>>)
 876                     -> mc::cmt<'tcx>
 877     {
 878         debug!("walk_autoref(expr.id={} cmt_derefd={} opt_autoref={:?})",
 879                expr.id,
 880                cmt_base.repr(self.tcx()),
 881                opt_autoref);
 882
 883         let cmt_base_ty = cmt_base.ty;
 884
 885         let autoref = match opt_autoref {
 886             Some(ref autoref) => autoref,
 887             None => {
 888                 // No AutoRef.
 889                 return cmt_base;
 890             }
 891         };
 892
 893         debug!("walk_autoref: expr.id={} cmt_base={}",
 894                expr.id,
 895                cmt_base.repr(self.tcx()));
 896
 897         match *autoref {
 898             ty::AutoPtr(r, m) => {
 899                 self.delegate.borrow(expr.id,
 900                                      expr.span,
 901                                      cmt_base,
 902                                      *r,
 903                                      ty::BorrowKind::from_mutbl(m),
 904                                      AutoRef);
 905             }
 906
 907             ty::AutoUnsafe(m) => {
 908                 debug!("walk_autoref: expr.id={} cmt_base={}",
 909                        expr.id,
 910                        cmt_base.repr(self.tcx()));
 911
 912                 // Converting from a &T to *T (or &mut T to *mut T) is
 913                 // treated as borrowing it for the enclosing temporary
 914                 // scope.
 915                 let r = ty::ReScope(region::CodeExtent::from_node_id(expr.id));
 916
 917                 self.delegate.borrow(expr.id,
 918                                      expr.span,
 919                                      cmt_base,
 920                                      r,
 921                                      ty::BorrowKind::from_mutbl(m),
 922                                      AutoUnsafe);
 923             }
 924         }
 925
 926         // Construct the categorization for the result of the autoref.
 927         // This is always an rvalue, since we are producing a new
 928         // (temporary) indirection.
 929
 930         let adj_ty =
 931             ty::adjust_ty_for_autoref(self.tcx(),
 932                                       cmt_base_ty,
 933                                       opt_autoref);
 934
 935         self.mc.cat_rvalue_node(expr.id, expr.span, adj_ty)
 936     }
 937
 938
 939     // When this returns true, it means that the expression *is* a
 940     // method-call (i.e. via the operator-overload).  This true result
 941     // also implies that walk_overloaded_operator already took care of
 942     // recursively processing the input arguments, and thus the caller
 943     // should not do so.
 944     fn walk_overloaded_operator(&mut self,
 945                                 expr: &ast::Expr,
 946                                 receiver: &ast::Expr,
 947                                 rhs: Vec<&ast::Expr>,
 948                                 pass_args: PassArgs)
 949                                 -> bool
 950     {
 951         if !self.typer.is_method_call(expr.id) {
 952             return false;
 953         }
 954
 955         match pass_args {
 956             PassArgs::ByValue => {
 957                 self.consume_expr(receiver);
 958                 for &arg in &rhs {
 959                     self.consume_expr(arg);
 960                 }
 961
 962                 return true;
 963             },
 964             PassArgs::ByRef => {},
 965         }
 966
 967         self.walk_expr(receiver);
 968
 969         // Arguments (but not receivers) to overloaded operator
 970         // methods are implicitly autoref'd which sadly does not use
 971         // adjustments, so we must hardcode the borrow here.
 972
 973         let r = ty::ReScope(region::CodeExtent::from_node_id(expr.id));
 974         let bk = ty::ImmBorrow;
 975
 976         for &arg in &rhs {
 977             self.borrow_expr(arg, r, bk, OverloadedOperator);
 978         }
 979         return true;
 980     }
 981
 982     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm) -> TrackMatchMode {
 983         let mut mode = Unknown;
 984         for pat in &arm.pats {
 985             self.determine_pat_move_mode(discr_cmt.clone(), &**pat, &mut mode);
 986         }
 987         mode
 988     }
 989
 990     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm, mode: MatchMode) {
 991         for pat in &arm.pats {
 992             self.walk_pat(discr_cmt.clone(), &**pat, mode);
 993         }
 994
 995         if let Some(ref guard) = arm.guard {
 996             self.consume_expr(&**guard);
 997         }
 998
 999         self.consume_expr(&*arm.body);
1000     }
1001
1002     /// Walks an pat that occurs in isolation (i.e. top-level of fn
1003     /// arg or let binding.  *Not* a match arm or nested pat.)
1004     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &ast::Pat) {
1005         let mut mode = Unknown;
1006         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
1007         let mode = mode.match_mode();
1008         self.walk_pat(cmt_discr, pat, mode);
1009     }
1010
1011     /// Identifies any bindings within `pat` and accumulates within
1012     /// `mode` whether the overall pattern/match structure is a move,
1013     /// copy, or borrow.
1014     fn determine_pat_move_mode(&mut self,
1015                                cmt_discr: mc::cmt<'tcx>,
1016                                pat: &ast::Pat,
1017                                mode: &mut TrackMatchMode) {
1018         debug!("determine_pat_move_mode cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
1019                pat.repr(self.tcx()));
1020         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
1021             let tcx = self.tcx();
1022             let def_map = &self.tcx().def_map;
1023             if pat_util::pat_is_binding(def_map, pat) {
1024                 match pat.node {
1025                     ast::PatIdent(ast::BindByRef(_), _, _) =>
1026                         mode.lub(BorrowingMatch),
1027                     ast::PatIdent(ast::BindByValue(_), _, _) => {
1028                         match copy_or_move(self.typer, &cmt_pat, PatBindingMove) {
1029                             Copy => mode.lub(CopyingMatch),
1030                             Move(_) => mode.lub(MovingMatch),
1031                         }
1032                     }
1033                     _ => {
1034                         tcx.sess.span_bug(
1035                             pat.span,
1036                             "binding pattern not an identifier");
1037                     }
1038                 }
1039             }
1040         }));
1041     }
1042
1043     /// The core driver for walking a pattern; `match_mode` must be
1044     /// established up front, e.g. via `determine_pat_move_mode` (see
1045     /// also `walk_irrefutable_pat` for patterns that stand alone).
1046     fn walk_pat(&mut self,
1047                 cmt_discr: mc::cmt<'tcx>,
1048                 pat: &ast::Pat,
1049                 match_mode: MatchMode) {
1050         debug!("walk_pat cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
1051                pat.repr(self.tcx()));
1052
1053         let mc = &self.mc;
1054         let typer = self.typer;
1055         let def_map = &self.tcx().def_map;
1056         let delegate = &mut self.delegate;
1057         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
1058             if pat_util::pat_is_binding(def_map, pat) {
1059                 let tcx = typer.tcx();
1060
1061                 debug!("binding cmt_pat={} pat={} match_mode={:?}",
1062                        cmt_pat.repr(tcx),
1063                        pat.repr(tcx),
1064                        match_mode);
1065
1066                 // pat_ty: the type of the binding being produced.
1067                 let pat_ty = return_if_err!(typer.node_ty(pat.id));
1068
1069                 // Each match binding is effectively an assignment to the
1070                 // binding being produced.
1071                 let def = def_map.borrow().get(&pat.id).unwrap().full_def();
1072                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
1073                     Ok(binding_cmt) => {
1074                         delegate.mutate(pat.id, pat.span, binding_cmt, Init);
1075                     }
1076                     Err(_) => { }
1077                 }
1078
1079                 // It is also a borrow or copy/move of the value being matched.
1080                 match pat.node {
1081                     ast::PatIdent(ast::BindByRef(m), _, _) => {
1082                         let (r, bk) = {
1083                             (ty::ty_region(tcx, pat.span, pat_ty),
1084                              ty::BorrowKind::from_mutbl(m))
1085                         };
1086                         delegate.borrow(pat.id, pat.span, cmt_pat,
1087                                              r, bk, RefBinding);
1088                     }
1089                     ast::PatIdent(ast::BindByValue(_), _, _) => {
1090                         let mode = copy_or_move(typer, &cmt_pat, PatBindingMove);
1091                         debug!("walk_pat binding consuming pat");
1092                         delegate.consume_pat(pat, cmt_pat, mode);
1093                     }
1094                     _ => {
1095                         tcx.sess.span_bug(
1096                             pat.span,
1097                             "binding pattern not an identifier");
1098                     }
1099                 }
1100             } else {
1101                 match pat.node {
1102                     ast::PatVec(_, Some(ref slice_pat), _) => {
1103                         // The `slice_pat` here creates a slice into
1104                         // the original vector.  This is effectively a
1105                         // borrow of the elements of the vector being
1106                         // matched.
1107
1108                         let (slice_cmt, slice_mutbl, slice_r) =
1109                             return_if_err!(mc.cat_slice_pattern(cmt_pat, &**slice_pat));
1110
1111                         // Note: We declare here that the borrow
1112                         // occurs upon entering the `[...]`
1113                         // pattern. This implies that something like
1114                         // `[a; b]` where `a` is a move is illegal,
1115                         // because the borrow is already in effect.
1116                         // In fact such a move would be safe-ish, but
1117                         // it effectively *requires* that we use the
1118                         // nulling out semantics to indicate when a
1119                         // value has been moved, which we are trying
1120                         // to move away from.  Otherwise, how can we
1121                         // indicate that the first element in the
1122                         // vector has been moved?  Eventually, we
1123                         // could perhaps modify this rule to permit
1124                         // `[..a, b]` where `b` is a move, because in
1125                         // that case we can adjust the length of the
1126                         // original vec accordingly, but we'd have to
1127                         // make trans do the right thing, and it would
1128                         // only work for `~` vectors. It seems simpler
1129                         // to just require that people call
1130                         // `vec.pop()` or `vec.unshift()`.
1131                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
1132                         delegate.borrow(pat.id, pat.span,
1133                                         slice_cmt, slice_r,
1134                                         slice_bk, RefBinding);
1135                     }
1136                     _ => { }
1137                 }
1138             }
1139         }));
1140
1141         // Do a second pass over the pattern, calling `matched_pat` on
1142         // the interior nodes (enum variants and structs), as opposed
1143         // to the above loop's visit of than the bindings that form
1144         // the leaves of the pattern tree structure.
1145         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
1146             let def_map = def_map.borrow();
1147             let tcx = typer.tcx();
1148
1149             match pat.node {
1150                 ast::PatEnum(_, _) | ast::PatQPath(..) |
1151                 ast::PatIdent(_, _, None) | ast::PatStruct(..) => {
1152                     match def_map.get(&pat.id).map(|d| d.full_def()) {
1153                         None => {
1154                             // no definition found: pat is not a
1155                             // struct or enum pattern.
1156                         }
1157
1158                         Some(def::DefVariant(enum_did, variant_did, _is_struct)) => {
1159                             let downcast_cmt =
1160                                 if ty::enum_is_univariant(tcx, enum_did) {
1161                                     cmt_pat
1162                                 } else {
1163                                     let cmt_pat_ty = cmt_pat.ty;
1164                                     mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1165                                 };
1166
1167                             debug!("variant downcast_cmt={} pat={}",
1168                                    downcast_cmt.repr(tcx),
1169                                    pat.repr(tcx));
1170
1171                             delegate.matched_pat(pat, downcast_cmt, match_mode);
1172                         }
1173
1174                         Some(def::DefStruct(..)) | Some(def::DefTy(_, false)) => {
1175                             // A struct (in either the value or type
1176                             // namespace; we encounter the former on
1177                             // e.g. patterns for unit structs).
1178
1179                             debug!("struct cmt_pat={} pat={}",
1180                                    cmt_pat.repr(tcx),
1181                                    pat.repr(tcx));
1182
1183                             delegate.matched_pat(pat, cmt_pat, match_mode);
1184                         }
1185
1186                         Some(def::DefConst(..)) |
1187                         Some(def::DefAssociatedConst(..)) |
1188                         Some(def::DefLocal(..)) => {
1189                             // This is a leaf (i.e. identifier binding
1190                             // or constant value to match); thus no
1191                             // `matched_pat` call.
1192                         }
1193
1194                         Some(def @ def::DefTy(_, true)) => {
1195                             // An enum's type -- should never be in a
1196                             // pattern.
1197
1198                             if !tcx.sess.has_errors() {
1199                                 let msg = format!("Pattern has unexpected type: {:?} and type {}",
1200                                                   def,
1201                                                   cmt_pat.ty.repr(tcx));
1202                                 tcx.sess.span_bug(pat.span, &msg)
1203                             }
1204                         }
1205
1206                         Some(def) => {
1207                             // Remaining cases are e.g. DefFn, to
1208                             // which identifiers within patterns
1209                             // should not resolve. However, we do
1210                             // encouter this when using the
1211                             // expr-use-visitor during typeck. So just
1212                             // ignore it, an error should have been
1213                             // reported.
1214
1215                             if !tcx.sess.has_errors() {
1216                                 let msg = format!("Pattern has unexpected def: {:?} and type {}",
1217                                                   def,
1218                                                   cmt_pat.ty.repr(tcx));
1219                                 tcx.sess.span_bug(pat.span, &msg[..])
1220                             }
1221                         }
1222                     }
1223                 }
1224
1225                 ast::PatIdent(_, _, Some(_)) => {
1226                     // Do nothing; this is a binding (not a enum
1227                     // variant or struct), and the cat_pattern call
1228                     // will visit the substructure recursively.
1229                 }
1230
1231                 ast::PatWild(_) | ast::PatTup(..) | ast::PatBox(..) |
1232                 ast::PatRegion(..) | ast::PatLit(..) | ast::PatRange(..) |
1233                 ast::PatVec(..) | ast::PatMac(..) => {
1234                     // Similarly, each of these cases does not
1235                     // correspond to a enum variant or struct, so we
1236                     // do not do any `matched_pat` calls for these
1237                     // cases either.
1238                 }
1239             }
1240         }));
1241     }
1242
1243     fn walk_captures(&mut self, closure_expr: &ast::Expr) {
1244         debug!("walk_captures({})", closure_expr.repr(self.tcx()));
1245
1246         ty::with_freevars(self.tcx(), closure_expr.id, |freevars| {
1247             for freevar in freevars {
1248                 let id_var = freevar.def.def_id().node;
1249                 let upvar_id = ty::UpvarId { var_id: id_var,
1250                                              closure_expr_id: closure_expr.id };
1251                 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
1252                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1253                                                                    closure_expr.span,
1254                                                                    freevar.def));
1255                 match upvar_capture {
1256                     ty::UpvarCapture::ByValue => {
1257                         let mode = copy_or_move(self.typer, &cmt_var, CaptureMove);
1258                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1259                     }
1260                     ty::UpvarCapture::ByRef(upvar_borrow) => {
1261                         self.delegate.borrow(closure_expr.id,
1262                                              closure_expr.span,
1263                                              cmt_var,
1264                                              upvar_borrow.region,
1265                                              upvar_borrow.kind,
1266                                              ClosureCapture(freevar.span));
1267                     }
1268                 }
1269             }
1270         });
1271     }
1272
1273     fn cat_captured_var(&mut self,
1274                         closure_id: ast::NodeId,
1275                         closure_span: Span,
1276                         upvar_def: def::Def)
1277                         -> mc::McResult<mc::cmt<'tcx>> {
1278         // Create the cmt for the variable being borrowed, from the
1279         // caller's perspective
1280         let var_id = upvar_def.def_id().node;
1281         let var_ty = try!(self.typer.node_ty(var_id));
1282         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1283     }
1284 }
1285
1286 fn copy_or_move<'tcx>(typer: &mc::Typer<'tcx>,
1287                       cmt: &mc::cmt<'tcx>,
1288                       move_reason: MoveReason)
1289                       -> ConsumeMode
1290 {
1291     if typer.type_moves_by_default(cmt.span, cmt.ty) {
1292         Move(move_reason)
1293     } else {
1294         Copy
1295     }
1296 }