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 /*!
  12  * A different sort of visitor for walking fn bodies.  Unlike the
  13  * normal visitor, which just walks the entire body in one shot, the
  14  * `ExprUseVisitor` determines how expressions are being used.
  15  */
  16
  17 use mc = middle::mem_categorization;
  18 use middle::def;
  19 use middle::freevars;
  20 use middle::pat_util;
  21 use middle::ty;
  22 use middle::typeck::MethodCall;
  23 use middle::typeck;
  24 use syntax::ast;
  25 use syntax::codemap::{Span};
  26 use util::ppaux::Repr;
  27
  28 ///////////////////////////////////////////////////////////////////////////
  29 // The Delegate trait
  30
  31 /// This trait defines the callbacks you can expect to receive when
  32 /// employing the ExprUseVisitor.
  33 pub trait Delegate {
  34     // The value found at `cmt` is either copied or moved, depending
  35     // on mode.
  36     fn consume(&mut self,
  37                consume_id: ast::NodeId,
  38                consume_span: Span,
  39                cmt: mc::cmt,
  40                mode: ConsumeMode);
  41
  42     // The value found at `cmt` is either copied or moved via the
  43     // pattern binding `consume_pat`, depending on mode.
  44     fn consume_pat(&mut self,
  45                    consume_pat: &ast::Pat,
  46                    cmt: mc::cmt,
  47                    mode: ConsumeMode);
  48
  49     // The value found at `borrow` is being borrowed at the point
  50     // `borrow_id` for the region `loan_region` with kind `bk`.
  51     fn borrow(&mut self,
  52               borrow_id: ast::NodeId,
  53               borrow_span: Span,
  54               cmt: mc::cmt,
  55               loan_region: ty::Region,
  56               bk: ty::BorrowKind,
  57               loan_cause: LoanCause);
  58
  59     // The local variable `id` is declared but not initialized.
  60     fn decl_without_init(&mut self,
  61                          id: ast::NodeId,
  62                          span: Span);
  63
  64     // The path at `cmt` is being assigned to.
  65     fn mutate(&mut self,
  66               assignment_id: ast::NodeId,
  67               assignment_span: Span,
  68               assignee_cmt: mc::cmt,
  69               mode: MutateMode);
  70 }
  71
  72 #[deriving(PartialEq)]
  73 pub enum LoanCause {
  74     ClosureCapture(Span),
  75     AddrOf,
  76     AutoRef,
  77     RefBinding,
  78     OverloadedOperator,
  79     ClosureInvocation
  80 }
  81
  82 #[deriving(PartialEq,Show)]
  83 pub enum ConsumeMode {
  84     Copy,                // reference to x where x has a type that copies
  85     Move(MoveReason),    // reference to x where x has a type that moves
  86 }
  87
  88 #[deriving(PartialEq,Show)]
  89 pub enum MoveReason {
  90     DirectRefMove,
  91     PatBindingMove,
  92     CaptureMove,
  93 }
  94
  95 #[deriving(PartialEq,Show)]
  96 pub enum MutateMode {
  97     Init,
  98     JustWrite,    // x = y
  99     WriteAndRead, // x += y
 100 }
 101
 102 ///////////////////////////////////////////////////////////////////////////
 103 // The ExprUseVisitor type
 104 //
 105 // This is the code that actually walks the tree. Like
 106 // mem_categorization, it requires a TYPER, which is a type that
 107 // supplies types from the tree. After type checking is complete, you
 108 // can just use the tcx as the typer.
 109
 110 pub struct ExprUseVisitor<'d,'t,TYPER> {
 111     typer: &'t TYPER,
 112     mc: mc::MemCategorizationContext<'t,TYPER>,
 113     delegate: &'d mut Delegate,
 114 }
 115
 116 // If the TYPER results in an error, it's because the type check
 117 // failed (or will fail, when the error is uncovered and reported
 118 // during writeback). In this case, we just ignore this part of the
 119 // code.
 120 //
 121 // Note that this macro appears similar to try!(), but, unlike try!(),
 122 // it does not propagate the error.
 123 macro_rules! return_if_err(
 124     ($inp: expr) => (
 125         match $inp {
 126             Ok(v) => v,
 127             Err(()) => return
 128         }
 129     )
 130 )
 131
 132 impl<'d,'t,TYPER:mc::Typer> ExprUseVisitor<'d,'t,TYPER> {
 133     pub fn new(delegate: &'d mut Delegate,
 134                typer: &'t TYPER)
 135                -> ExprUseVisitor<'d,'t,TYPER> {
 136         ExprUseVisitor { typer: typer,
 137                          mc: mc::MemCategorizationContext::new(typer),
 138                          delegate: delegate }
 139     }
 140
 141     pub fn walk_fn(&mut self,
 142                    decl: &ast::FnDecl,
 143                    body: &ast::Block) {
 144         self.walk_arg_patterns(decl, body);
 145         self.walk_block(body);
 146     }
 147
 148     fn walk_arg_patterns(&mut self,
 149                          decl: &ast::FnDecl,
 150                          body: &ast::Block) {
 151         for arg in decl.inputs.iter() {
 152             let arg_ty = ty::node_id_to_type(self.tcx(), arg.pat.id);
 153
 154             let arg_cmt = self.mc.cat_rvalue(
 155                 arg.id,
 156                 arg.pat.span,
 157                 ty::ReScope(body.id), // Args live only as long as the fn body.
 158                 arg_ty);
 159
 160             self.walk_pat(arg_cmt, arg.pat);
 161         }
 162     }
 163
 164     fn tcx<'a>(&'a self) -> &'a ty::ctxt {
 165         self.typer.tcx()
 166     }
 167
 168     fn delegate_consume(&mut self,
 169                         consume_id: ast::NodeId,
 170                         consume_span: Span,
 171                         cmt: mc::cmt) {
 172         let mode = copy_or_move(self.tcx(), cmt.ty, DirectRefMove);
 173         self.delegate.consume(consume_id, consume_span, cmt, mode);
 174     }
 175
 176     fn consume_exprs(&mut self, exprs: &Vec<@ast::Expr>) {
 177         for &expr in exprs.iter() {
 178             self.consume_expr(expr);
 179         }
 180     }
 181
 182     fn consume_expr(&mut self, expr: &ast::Expr) {
 183         debug!("consume_expr(expr={})", expr.repr(self.tcx()));
 184
 185         let cmt = return_if_err!(self.mc.cat_expr(expr));
 186         self.delegate_consume(expr.id, expr.span, cmt);
 187
 188         match expr.node {
 189             ast::ExprParen(subexpr) => {
 190                 // Argh but is ExprParen horrible. So, if we consume
 191                 // `(x)`, that generally is also consuming `x`, UNLESS
 192                 // there are adjustments on the `(x)` expression
 193                 // (e.g., autoderefs and autorefs).
 194                 if self.typer.adjustments().borrow().contains_key(&expr.id) {
 195                     self.walk_expr(expr);
 196                 } else {
 197                     self.consume_expr(subexpr);
 198                 }
 199             }
 200
 201             _ => {
 202                 self.walk_expr(expr)
 203             }
 204         }
 205     }
 206
 207     fn mutate_expr(&mut self,
 208                    assignment_expr: &ast::Expr,
 209                    expr: &ast::Expr,
 210                    mode: MutateMode) {
 211         let cmt = return_if_err!(self.mc.cat_expr(expr));
 212         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 213         self.walk_expr(expr);
 214     }
 215
 216     fn borrow_expr(&mut self,
 217                    expr: &ast::Expr,
 218                    r: ty::Region,
 219                    bk: ty::BorrowKind,
 220                    cause: LoanCause) {
 221         debug!("borrow_expr(expr={}, r={}, bk={})",
 222                expr.repr(self.tcx()), r.repr(self.tcx()), bk.repr(self.tcx()));
 223
 224         let cmt = return_if_err!(self.mc.cat_expr(expr));
 225         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 226
 227         // Note: Unlike consume, we can ignore ExprParen. cat_expr
 228         // already skips over them, and walk will uncover any
 229         // attachments or whatever.
 230         self.walk_expr(expr)
 231     }
 232
 233     fn select_from_expr(&mut self, expr: &ast::Expr) {
 234         self.walk_expr(expr)
 235     }
 236
 237     fn walk_expr(&mut self, expr: &ast::Expr) {
 238         debug!("walk_expr(expr={})", expr.repr(self.tcx()));
 239
 240         self.walk_adjustment(expr);
 241
 242         match expr.node {
 243             ast::ExprParen(subexpr) => {
 244                 self.walk_expr(subexpr)
 245             }
 246
 247             ast::ExprPath(..) => { }
 248
 249             ast::ExprUnary(ast::UnDeref, base) => {      // *base
 250                 if !self.walk_overloaded_operator(expr, base, []) {
 251                     self.select_from_expr(base);
 252                 }
 253             }
 254
 255             ast::ExprField(base, _, _) => {         // base.f
 256                 self.select_from_expr(base);
 257             }
 258
 259             ast::ExprIndex(lhs, rhs) => {           // lhs[rhs]
 260                 if !self.walk_overloaded_operator(expr, lhs, [rhs]) {
 261                     self.select_from_expr(lhs);
 262                     self.consume_expr(rhs);
 263                 }
 264             }
 265
 266             ast::ExprCall(callee, ref args) => {    // callee(args)
 267                 self.walk_callee(expr, callee);
 268                 self.consume_exprs(args);
 269             }
 270
 271             ast::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 272                 self.consume_exprs(args);
 273             }
 274
 275             ast::ExprStruct(_, ref fields, opt_with) => {
 276                 self.walk_struct_expr(expr, fields, opt_with);
 277             }
 278
 279             ast::ExprTup(ref exprs) => {
 280                 self.consume_exprs(exprs);
 281             }
 282
 283             ast::ExprIf(cond_expr, then_blk, opt_else_expr) => {
 284                 self.consume_expr(cond_expr);
 285                 self.walk_block(then_blk);
 286                 for else_expr in opt_else_expr.iter() {
 287                     self.consume_expr(*else_expr);
 288                 }
 289             }
 290
 291             ast::ExprMatch(discr, ref arms) => {
 292                 // treatment of the discriminant is handled while
 293                 // walking the arms:
 294                 self.walk_expr(discr);
 295                 let discr_cmt = return_if_err!(self.mc.cat_expr(discr));
 296                 for arm in arms.iter() {
 297                     self.walk_arm(discr_cmt.clone(), arm);
 298                 }
 299             }
 300
 301             ast::ExprVec(ref exprs) => {
 302                 self.consume_exprs(exprs);
 303             }
 304
 305             ast::ExprAddrOf(m, base) => {   // &base
 306                 // make sure that the thing we are pointing out stays valid
 307                 // for the lifetime `scope_r` of the resulting ptr:
 308                 let expr_ty = ty::expr_ty(self.tcx(), expr);
 309                 if !ty::type_is_bot(expr_ty) {
 310                     let r = ty::ty_region(self.tcx(), expr.span, expr_ty);
 311                     let bk = ty::BorrowKind::from_mutbl(m);
 312                     self.borrow_expr(base, r, bk, AddrOf);
 313                 } else {
 314                     self.walk_expr(base);
 315                 }
 316             }
 317
 318             ast::ExprInlineAsm(ref ia) => {
 319                 for &(_, input) in ia.inputs.iter() {
 320                     self.consume_expr(input);
 321                 }
 322
 323                 for &(_, output) in ia.outputs.iter() {
 324                     self.mutate_expr(expr, output, JustWrite);
 325                 }
 326             }
 327
 328             ast::ExprBreak(..) |
 329             ast::ExprAgain(..) |
 330             ast::ExprLit(..) => {}
 331
 332             ast::ExprLoop(blk, _) => {
 333                 self.walk_block(blk);
 334             }
 335
 336             ast::ExprWhile(cond_expr, blk) => {
 337                 self.consume_expr(cond_expr);
 338                 self.walk_block(blk);
 339             }
 340
 341             ast::ExprForLoop(..) => fail!("non-desugared expr_for_loop"),
 342
 343             ast::ExprUnary(_, lhs) => {
 344                 if !self.walk_overloaded_operator(expr, lhs, []) {
 345                     self.consume_expr(lhs);
 346                 }
 347             }
 348
 349             ast::ExprBinary(_, lhs, rhs) => {
 350                 if !self.walk_overloaded_operator(expr, lhs, [rhs]) {
 351                     self.consume_expr(lhs);
 352                     self.consume_expr(rhs);
 353                 }
 354             }
 355
 356             ast::ExprBlock(blk) => {
 357                 self.walk_block(blk);
 358             }
 359
 360             ast::ExprRet(ref opt_expr) => {
 361                 for expr in opt_expr.iter() {
 362                     self.consume_expr(*expr);
 363                 }
 364             }
 365
 366             ast::ExprAssign(lhs, rhs) => {
 367                 self.mutate_expr(expr, lhs, JustWrite);
 368                 self.consume_expr(rhs);
 369             }
 370
 371             ast::ExprCast(base, _) => {
 372                 self.consume_expr(base);
 373             }
 374
 375             ast::ExprAssignOp(_, lhs, rhs) => {
 376                 // This will have to change if/when we support
 377                 // overloaded operators for `+=` and so forth.
 378                 self.mutate_expr(expr, lhs, WriteAndRead);
 379                 self.consume_expr(rhs);
 380             }
 381
 382             ast::ExprRepeat(base, count) => {
 383                 self.consume_expr(base);
 384                 self.consume_expr(count);
 385             }
 386
 387             ast::ExprFnBlock(..) |
 388             ast::ExprProc(..) => {
 389                 self.walk_captures(expr)
 390             }
 391
 392             ast::ExprVstore(base, _) => {
 393                 self.consume_expr(base);
 394             }
 395
 396             ast::ExprBox(place, base) => {
 397                 self.consume_expr(place);
 398                 self.consume_expr(base);
 399             }
 400
 401             ast::ExprMac(..) => {
 402                 self.tcx().sess.span_bug(
 403                     expr.span,
 404                     "macro expression remains after expansion");
 405             }
 406         }
 407     }
 408
 409     fn walk_callee(&mut self, call: &ast::Expr, callee: &ast::Expr) {
 410         let callee_ty = ty::expr_ty_adjusted(self.tcx(), callee);
 411         debug!("walk_callee: callee={} callee_ty={}",
 412                callee.repr(self.tcx()), callee_ty.repr(self.tcx()));
 413         match ty::get(callee_ty).sty {
 414             ty::ty_bare_fn(..) => {
 415                 self.consume_expr(callee);
 416             }
 417             ty::ty_closure(ref f) => {
 418                 match f.onceness {
 419                     ast::Many => {
 420                         self.borrow_expr(callee,
 421                                          ty::ReScope(call.id),
 422                                          ty::UniqueImmBorrow,
 423                                          ClosureInvocation);
 424                     }
 425                     ast::Once => {
 426                         self.consume_expr(callee);
 427                     }
 428                 }
 429             }
 430             _ => {
 431                 match self.tcx()
 432                           .method_map
 433                           .borrow()
 434                           .find(&MethodCall::expr(call.id)) {
 435                     Some(_) => {
 436                         // FIXME(#14774, pcwalton): Implement this.
 437                     }
 438                     None => {
 439                         self.tcx().sess.span_bug(
 440                             callee.span,
 441                             format!("unxpected callee type {}",
 442                                     callee_ty.repr(self.tcx())).as_slice());
 443                     }
 444                 }
 445             }
 446         }
 447     }
 448
 449     fn walk_stmt(&mut self, stmt: &ast::Stmt) {
 450         match stmt.node {
 451             ast::StmtDecl(decl, _) => {
 452                 match decl.node {
 453                     ast::DeclLocal(local) => {
 454                         self.walk_local(local);
 455                     }
 456
 457                     ast::DeclItem(_) => {
 458                         // we don't visit nested items in this visitor,
 459                         // only the fn body we were given.
 460                     }
 461                 }
 462             }
 463
 464             ast::StmtExpr(expr, _) |
 465             ast::StmtSemi(expr, _) => {
 466                 self.consume_expr(expr);
 467             }
 468
 469             ast::StmtMac(..) => {
 470                 self.tcx().sess.span_bug(stmt.span, "unexpanded stmt macro");
 471             }
 472         }
 473     }
 474
 475     fn walk_local(&mut self, local: @ast::Local) {
 476         match local.init {
 477             None => {
 478                 let delegate = &mut self.delegate;
 479                 pat_util::pat_bindings(&self.typer.tcx().def_map, local.pat, |_, id, span, _| {
 480                     delegate.decl_without_init(id, span);
 481                 })
 482             }
 483
 484             Some(expr) => {
 485                 // Variable declarations with
 486                 // initializers are considered
 487                 // "assigns", which is handled by
 488                 // `walk_pat`:
 489                 self.walk_expr(expr);
 490                 let init_cmt = return_if_err!(self.mc.cat_expr(expr));
 491                 self.walk_pat(init_cmt, local.pat);
 492             }
 493         }
 494     }
 495
 496     fn walk_block(&mut self, blk: &ast::Block) {
 497         /*!
 498          * Indicates that the value of `blk` will be consumed,
 499          * meaning either copied or moved depending on its type.
 500          */
 501
 502         debug!("walk_block(blk.id={:?})", blk.id);
 503
 504         for stmt in blk.stmts.iter() {
 505             self.walk_stmt(*stmt);
 506         }
 507
 508         for tail_expr in blk.expr.iter() {
 509             self.consume_expr(*tail_expr);
 510         }
 511     }
 512
 513     fn walk_struct_expr(&mut self,
 514                         _expr: &ast::Expr,
 515                         fields: &Vec<ast::Field>,
 516                         opt_with: Option<@ast::Expr>) {
 517         // Consume the expressions supplying values for each field.
 518         for field in fields.iter() {
 519             self.consume_expr(field.expr);
 520         }
 521
 522         let with_expr = match opt_with {
 523             Some(w) => { w }
 524             None => { return; }
 525         };
 526
 527         let with_cmt = return_if_err!(self.mc.cat_expr(with_expr));
 528
 529         // Select just those fields of the `with`
 530         // expression that will actually be used
 531         let with_fields = match ty::get(with_cmt.ty).sty {
 532             ty::ty_struct(did, ref substs) => {
 533                 ty::struct_fields(self.tcx(), did, substs)
 534             }
 535             _ => {
 536                 self.tcx().sess.span_bug(
 537                     with_expr.span,
 538                     "with expression doesn't evaluate to a struct");
 539             }
 540         };
 541
 542         // Consume those fields of the with expression that are needed.
 543         for with_field in with_fields.iter() {
 544             if !contains_field_named(with_field, fields) {
 545                 let cmt_field = self.mc.cat_field(with_expr,
 546                                                   with_cmt.clone(),
 547                                                   with_field.ident,
 548                                                   with_field.mt.ty);
 549                 self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 550             }
 551         }
 552
 553         fn contains_field_named(field: &ty::field,
 554                                 fields: &Vec<ast::Field>)
 555                                 -> bool
 556         {
 557             fields.iter().any(
 558                 |f| f.ident.node.name == field.ident.name)
 559         }
 560     }
 561
 562     // Invoke the appropriate delegate calls for anything that gets
 563     // consumed or borrowed as part of the automatic adjustment
 564     // process.
 565     fn walk_adjustment(&mut self, expr: &ast::Expr) {
 566         let typer = self.typer;
 567         match typer.adjustments().borrow().find(&expr.id) {
 568             None => { }
 569             Some(adjustment) => {
 570                 match *adjustment {
 571                     ty::AutoAddEnv(..) |
 572                     ty::AutoObject(..) => {
 573                         // Creating an object or closure consumes the
 574                         // input and stores it into the resulting rvalue.
 575                         debug!("walk_adjustment(AutoAddEnv|AutoObject)");
 576                         let cmt_unadjusted =
 577                             return_if_err!(self.mc.cat_expr_unadjusted(expr));
 578                         self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 579                     }
 580                     ty::AutoDerefRef(ty::AutoDerefRef {
 581                         autoref: ref opt_autoref,
 582                         autoderefs: n
 583                     }) => {
 584                         self.walk_autoderefs(expr, n);
 585
 586                         match *opt_autoref {
 587                             None => { }
 588                             Some(ref r) => {
 589                                 self.walk_autoref(expr, r, n);
 590                             }
 591                         }
 592                     }
 593                 }
 594             }
 595         }
 596     }
 597
 598     fn walk_autoderefs(&mut self,
 599                        expr: &ast::Expr,
 600                        autoderefs: uint) {
 601         /*!
 602          * Autoderefs for overloaded Deref calls in fact reference
 603          * their receiver. That is, if we have `(*x)` where `x` is of
 604          * type `Rc<T>`, then this in fact is equivalent to
 605          * `x.deref()`. Since `deref()` is declared with `&self`, this
 606          * is an autoref of `x`.
 607          */
 608         debug!("walk_autoderefs expr={} autoderefs={}", expr.repr(self.tcx()), autoderefs);
 609
 610         for i in range(0, autoderefs) {
 611             let deref_id = typeck::MethodCall::autoderef(expr.id, i as u32);
 612             match self.typer.node_method_ty(deref_id) {
 613                 None => {}
 614                 Some(method_ty) => {
 615                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 616                     let self_ty = *ty::ty_fn_args(method_ty).get(0);
 617                     let (m, r) = match ty::get(self_ty).sty {
 618                         ty::ty_rptr(r, ref m) => (m.mutbl, r),
 619                         _ => self.tcx().sess.span_bug(expr.span,
 620                                 format!("bad overloaded deref type {}",
 621                                     method_ty.repr(self.tcx())).as_slice())
 622                     };
 623                     let bk = ty::BorrowKind::from_mutbl(m);
 624                     self.delegate.borrow(expr.id, expr.span, cmt,
 625                                          r, bk, AutoRef);
 626                 }
 627             }
 628         }
 629     }
 630
 631     fn walk_autoref(&mut self,
 632                     expr: &ast::Expr,
 633                     autoref: &ty::AutoRef,
 634                     autoderefs: uint) {
 635         debug!("walk_autoref expr={} autoderefs={}", expr.repr(self.tcx()), autoderefs);
 636
 637         let cmt_derefd = return_if_err!(
 638             self.mc.cat_expr_autoderefd(expr, autoderefs));
 639
 640         debug!("walk_autoref: cmt_derefd={}", cmt_derefd.repr(self.tcx()));
 641
 642         match *autoref {
 643             ty::AutoPtr(r, m) => {
 644                 self.delegate.borrow(expr.id,
 645                                      expr.span,
 646                                      cmt_derefd,
 647                                      r,
 648                                      ty::BorrowKind::from_mutbl(m),
 649                                      AutoRef)
 650             }
 651             ty::AutoBorrowVec(r, m) | ty::AutoBorrowVecRef(r, m) => {
 652                 let cmt_index = self.mc.cat_index(expr, cmt_derefd, autoderefs+1);
 653                 self.delegate.borrow(expr.id,
 654                                      expr.span,
 655                                      cmt_index,
 656                                      r,
 657                                      ty::BorrowKind::from_mutbl(m),
 658                                      AutoRef)
 659             }
 660             ty::AutoBorrowObj(r, m) => {
 661                 let cmt_deref = self.mc.cat_deref_obj(expr, cmt_derefd);
 662                 self.delegate.borrow(expr.id,
 663                                      expr.span,
 664                                      cmt_deref,
 665                                      r,
 666                                      ty::BorrowKind::from_mutbl(m),
 667                                      AutoRef)
 668             }
 669             ty::AutoUnsafe(_) => {}
 670         }
 671     }
 672
 673     fn walk_overloaded_operator(&mut self,
 674                                 expr: &ast::Expr,
 675                                 receiver: &ast::Expr,
 676                                 args: &[@ast::Expr])
 677                                 -> bool
 678     {
 679         if !self.typer.is_method_call(expr.id) {
 680             return false;
 681         }
 682
 683         self.walk_expr(receiver);
 684
 685         // Arguments (but not receivers) to overloaded operator
 686         // methods are implicitly autoref'd which sadly does not use
 687         // adjustments, so we must hardcode the borrow here.
 688
 689         let r = ty::ReScope(expr.id);
 690         let bk = ty::ImmBorrow;
 691
 692         for &arg in args.iter() {
 693             self.borrow_expr(arg, r, bk, OverloadedOperator);
 694         }
 695         return true;
 696     }
 697
 698     fn walk_arm(&mut self, discr_cmt: mc::cmt, arm: &ast::Arm) {
 699         for &pat in arm.pats.iter() {
 700             self.walk_pat(discr_cmt.clone(), pat);
 701         }
 702
 703         for guard in arm.guard.iter() {
 704             self.consume_expr(*guard);
 705         }
 706
 707         self.consume_expr(arm.body);
 708     }
 709
 710     fn walk_pat(&mut self, cmt_discr: mc::cmt, pat: @ast::Pat) {
 711         debug!("walk_pat cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
 712                pat.repr(self.tcx()));
 713         let mc = &self.mc;
 714         let typer = self.typer;
 715         let tcx = typer.tcx();
 716         let def_map = &self.typer.tcx().def_map;
 717         let delegate = &mut self.delegate;
 718         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
 719             if pat_util::pat_is_binding(def_map, pat) {
 720                 let tcx = typer.tcx();
 721
 722                 debug!("binding cmt_pat={} pat={}",
 723                        cmt_pat.repr(tcx),
 724                        pat.repr(tcx));
 725
 726                 // pat_ty: the type of the binding being produced.
 727                 let pat_ty = ty::node_id_to_type(tcx, pat.id);
 728
 729                 // Each match binding is effectively an assignment to the
 730                 // binding being produced.
 731                 let def = def_map.borrow().get_copy(&pat.id);
 732                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
 733                     Ok(binding_cmt) => {
 734                         delegate.mutate(pat.id, pat.span, binding_cmt, Init);
 735                     }
 736                     Err(_) => { }
 737                 }
 738
 739                 // It is also a borrow or copy/move of the value being matched.
 740                 match pat.node {
 741                     ast::PatIdent(ast::BindByRef(m), _, _) => {
 742                         let (r, bk) = {
 743                             (ty::ty_region(tcx, pat.span, pat_ty),
 744                              ty::BorrowKind::from_mutbl(m))
 745                         };
 746                         delegate.borrow(pat.id, pat.span, cmt_pat,
 747                                              r, bk, RefBinding);
 748                     }
 749                     ast::PatIdent(ast::BindByValue(_), _, _) => {
 750                         let mode = copy_or_move(typer.tcx(), cmt_pat.ty, PatBindingMove);
 751                         delegate.consume_pat(pat, cmt_pat, mode);
 752                     }
 753                     _ => {
 754                         typer.tcx().sess.span_bug(
 755                             pat.span,
 756                             "binding pattern not an identifier");
 757                     }
 758                 }
 759             } else {
 760                 match pat.node {
 761                     ast::PatVec(_, Some(slice_pat), _) => {
 762                         // The `slice_pat` here creates a slice into
 763                         // the original vector.  This is effectively a
 764                         // borrow of the elements of the vector being
 765                         // matched.
 766
 767                         let (slice_cmt, slice_mutbl, slice_r) = {
 768                             match mc.cat_slice_pattern(cmt_pat, slice_pat) {
 769                                 Ok(v) => v,
 770                                 Err(()) => {
 771                                     tcx.sess.span_bug(slice_pat.span,
 772                                                       "Err from mc")
 773                                 }
 774                             }
 775                         };
 776
 777                         // Note: We declare here that the borrow
 778                         // occurs upon entering the `[...]`
 779                         // pattern. This implies that something like
 780                         // `[a, ..b]` where `a` is a move is illegal,
 781                         // because the borrow is already in effect.
 782                         // In fact such a move would be safe-ish, but
 783                         // it effectively *requires* that we use the
 784                         // nulling out semantics to indicate when a
 785                         // value has been moved, which we are trying
 786                         // to move away from.  Otherwise, how can we
 787                         // indicate that the first element in the
 788                         // vector has been moved?  Eventually, we
 789                         // could perhaps modify this rule to permit
 790                         // `[..a, b]` where `b` is a move, because in
 791                         // that case we can adjust the length of the
 792                         // original vec accordingly, but we'd have to
 793                         // make trans do the right thing, and it would
 794                         // only work for `~` vectors. It seems simpler
 795                         // to just require that people call
 796                         // `vec.pop()` or `vec.unshift()`.
 797                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
 798                         delegate.borrow(pat.id, pat.span,
 799                                         slice_cmt, slice_r,
 800                                         slice_bk, RefBinding);
 801                     }
 802                     _ => { }
 803                 }
 804             }
 805         }));
 806     }
 807
 808     fn walk_captures(&mut self, closure_expr: &ast::Expr) {
 809         debug!("walk_captures({})", closure_expr.repr(self.tcx()));
 810
 811         let tcx = self.typer.tcx();
 812         freevars::with_freevars(tcx, closure_expr.id, |freevars| {
 813             match freevars::get_capture_mode(self.tcx(), closure_expr.id) {
 814                 freevars::CaptureByRef => {
 815                     self.walk_by_ref_captures(closure_expr, freevars);
 816                 }
 817                 freevars::CaptureByValue => {
 818                     self.walk_by_value_captures(closure_expr, freevars);
 819                 }
 820             }
 821         });
 822     }
 823
 824     fn walk_by_ref_captures(&mut self,
 825                             closure_expr: &ast::Expr,
 826                             freevars: &[freevars::freevar_entry]) {
 827         for freevar in freevars.iter() {
 828             let id_var = freevar.def.def_id().node;
 829             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 830                                                                closure_expr.span,
 831                                                                freevar.def));
 832
 833             // Lookup the kind of borrow the callee requires, as
 834             // inferred by regionbk
 835             let upvar_id = ty::UpvarId { var_id: id_var,
 836                                          closure_expr_id: closure_expr.id };
 837             let upvar_borrow = self.tcx().upvar_borrow_map.borrow()
 838                                    .get_copy(&upvar_id);
 839
 840             self.delegate.borrow(closure_expr.id,
 841                                  closure_expr.span,
 842                                  cmt_var,
 843                                  upvar_borrow.region,
 844                                  upvar_borrow.kind,
 845                                  ClosureCapture(freevar.span));
 846         }
 847     }
 848
 849     fn walk_by_value_captures(&mut self,
 850                               closure_expr: &ast::Expr,
 851                               freevars: &[freevars::freevar_entry]) {
 852         for freevar in freevars.iter() {
 853             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 854                                                                closure_expr.span,
 855                                                                freevar.def));
 856             let mode = copy_or_move(self.tcx(), cmt_var.ty, CaptureMove);
 857             self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 858         }
 859     }
 860
 861     fn cat_captured_var(&mut self,
 862                         closure_id: ast::NodeId,
 863                         closure_span: Span,
 864                         upvar_def: def::Def)
 865                         -> mc::McResult<mc::cmt> {
 866         // Create the cmt for the variable being borrowed, from the
 867         // caller's perspective
 868         let var_id = upvar_def.def_id().node;
 869         let var_ty = ty::node_id_to_type(self.tcx(), var_id);
 870         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 871     }
 872 }
 873
 874 fn copy_or_move(tcx: &ty::ctxt, ty: ty::t, move_reason: MoveReason) -> ConsumeMode {
 875     if ty::type_moves_by_default(tcx, ty) { Move(move_reason) } else { Copy }
 876 }
 877