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 middle::mem_categorization as mc;
  18 use middle::def;
  19 use middle::mem_categorization::Typer;
  20 use middle::pat_util;
  21 use middle::ty;
  22 use middle::typeck::{MethodCall, MethodObject, MethodOrigin, MethodParam};
  23 use middle::typeck::{MethodStatic, MethodStaticUnboxedClosure};
  24 use middle::typeck;
  25 use util::ppaux::Repr;
  26
  27 use syntax::ast;
  28 use syntax::ptr::P;
  29 use syntax::codemap::Span;
  30
  31 ///////////////////////////////////////////////////////////////////////////
  32 // The Delegate trait
  33
  34 /// This trait defines the callbacks you can expect to receive when
  35 /// employing the ExprUseVisitor.
  36 pub trait Delegate {
  37     // The value found at `cmt` is either copied or moved, depending
  38     // on mode.
  39     fn consume(&mut self,
  40                consume_id: ast::NodeId,
  41                consume_span: Span,
  42                cmt: mc::cmt,
  43                mode: ConsumeMode);
  44
  45     // The value found at `cmt` is either copied or moved via the
  46     // pattern binding `consume_pat`, depending on mode.
  47     fn consume_pat(&mut self,
  48                    consume_pat: &ast::Pat,
  49                    cmt: mc::cmt,
  50                    mode: ConsumeMode);
  51
  52     // The value found at `borrow` is being borrowed at the point
  53     // `borrow_id` for the region `loan_region` with kind `bk`.
  54     fn borrow(&mut self,
  55               borrow_id: ast::NodeId,
  56               borrow_span: Span,
  57               cmt: mc::cmt,
  58               loan_region: ty::Region,
  59               bk: ty::BorrowKind,
  60               loan_cause: LoanCause);
  61
  62     // The local variable `id` is declared but not initialized.
  63     fn decl_without_init(&mut self,
  64                          id: ast::NodeId,
  65                          span: Span);
  66
  67     // The path at `cmt` is being assigned to.
  68     fn mutate(&mut self,
  69               assignment_id: ast::NodeId,
  70               assignment_span: Span,
  71               assignee_cmt: mc::cmt,
  72               mode: MutateMode);
  73 }
  74
  75 #[deriving(PartialEq)]
  76 pub enum LoanCause {
  77     ClosureCapture(Span),
  78     AddrOf,
  79     AutoRef,
  80     RefBinding,
  81     OverloadedOperator,
  82     ClosureInvocation,
  83     ForLoop,
  84 }
  85
  86 #[deriving(PartialEq,Show)]
  87 pub enum ConsumeMode {
  88     Copy,                // reference to x where x has a type that copies
  89     Move(MoveReason),    // reference to x where x has a type that moves
  90 }
  91
  92 #[deriving(PartialEq,Show)]
  93 pub enum MoveReason {
  94     DirectRefMove,
  95     PatBindingMove,
  96     CaptureMove,
  97 }
  98
  99 #[deriving(PartialEq,Show)]
 100 pub enum MutateMode {
 101     Init,
 102     JustWrite,    // x = y
 103     WriteAndRead, // x += y
 104 }
 105
 106 enum OverloadedCallType {
 107     FnOverloadedCall,
 108     FnMutOverloadedCall,
 109     FnOnceOverloadedCall,
 110 }
 111
 112 impl OverloadedCallType {
 113     fn from_trait_id(tcx: &ty::ctxt, trait_id: ast::DefId)
 114                      -> OverloadedCallType {
 115         for &(maybe_function_trait, overloaded_call_type) in [
 116             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 117             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 118             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 119         ].iter() {
 120             match maybe_function_trait {
 121                 Some(function_trait) if function_trait == trait_id => {
 122                     return overloaded_call_type
 123                 }
 124                 _ => continue,
 125             }
 126         }
 127
 128         tcx.sess.bug("overloaded call didn't map to known function trait")
 129     }
 130
 131     fn from_method_id(tcx: &ty::ctxt, method_id: ast::DefId)
 132                       -> OverloadedCallType {
 133         let method_descriptor = match ty::impl_or_trait_item(tcx, method_id) {
 134             ty::MethodTraitItem(ref method_descriptor) => {
 135                 (*method_descriptor).clone()
 136             }
 137             ty::TypeTraitItem(_) => {
 138                 tcx.sess.bug("overloaded call method wasn't in method map")
 139             }
 140         };
 141         let impl_id = match method_descriptor.container {
 142             ty::TraitContainer(_) => {
 143                 tcx.sess.bug("statically resolved overloaded call method \
 144                               belonged to a trait?!")
 145             }
 146             ty::ImplContainer(impl_id) => impl_id,
 147         };
 148         let trait_ref = match ty::impl_trait_ref(tcx, impl_id) {
 149             None => {
 150                 tcx.sess.bug("statically resolved overloaded call impl \
 151                               didn't implement a trait?!")
 152             }
 153             Some(ref trait_ref) => (*trait_ref).clone(),
 154         };
 155         OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 156     }
 157
 158     fn from_unboxed_closure(tcx: &ty::ctxt, closure_did: ast::DefId)
 159                             -> OverloadedCallType {
 160         let trait_did =
 161             tcx.unboxed_closures
 162                .borrow()
 163                .find(&closure_did)
 164                .expect("OverloadedCallType::from_unboxed_closure: didn't \
 165                         find closure id")
 166                .kind
 167                .trait_did(tcx);
 168         OverloadedCallType::from_trait_id(tcx, trait_did)
 169     }
 170
 171     fn from_method_origin(tcx: &ty::ctxt, origin: &MethodOrigin)
 172                           -> OverloadedCallType {
 173         match *origin {
 174             MethodStatic(def_id) => {
 175                 OverloadedCallType::from_method_id(tcx, def_id)
 176             }
 177             MethodStaticUnboxedClosure(def_id) => {
 178                 OverloadedCallType::from_unboxed_closure(tcx, def_id)
 179             }
 180             MethodParam(MethodParam { trait_ref: ref trait_ref, .. }) |
 181             MethodObject(MethodObject { trait_ref: ref trait_ref, .. }) => {
 182                 OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 183             }
 184         }
 185     }
 186 }
 187
 188 ///////////////////////////////////////////////////////////////////////////
 189 // The ExprUseVisitor type
 190 //
 191 // This is the code that actually walks the tree. Like
 192 // mem_categorization, it requires a TYPER, which is a type that
 193 // supplies types from the tree. After type checking is complete, you
 194 // can just use the tcx as the typer.
 195
 196 pub struct ExprUseVisitor<'d,'t,TYPER:'t> {
 197     typer: &'t TYPER,
 198     mc: mc::MemCategorizationContext<'t,TYPER>,
 199     delegate: &'d mut Delegate+'d,
 200 }
 201
 202 // If the TYPER results in an error, it's because the type check
 203 // failed (or will fail, when the error is uncovered and reported
 204 // during writeback). In this case, we just ignore this part of the
 205 // code.
 206 //
 207 // Note that this macro appears similar to try!(), but, unlike try!(),
 208 // it does not propagate the error.
 209 macro_rules! return_if_err(
 210     ($inp: expr) => (
 211         match $inp {
 212             Ok(v) => v,
 213             Err(()) => return
 214         }
 215     )
 216 )
 217
 218 impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,TYPER> {
 219     pub fn new(delegate: &'d mut Delegate,
 220                typer: &'t TYPER)
 221                -> ExprUseVisitor<'d,'t,TYPER> {
 222         ExprUseVisitor { typer: typer,
 223                          mc: mc::MemCategorizationContext::new(typer),
 224                          delegate: delegate }
 225     }
 226
 227     pub fn walk_fn(&mut self,
 228                    decl: &ast::FnDecl,
 229                    body: &ast::Block) {
 230         self.walk_arg_patterns(decl, body);
 231         self.walk_block(body);
 232     }
 233
 234     fn walk_arg_patterns(&mut self,
 235                          decl: &ast::FnDecl,
 236                          body: &ast::Block) {
 237         for arg in decl.inputs.iter() {
 238             let arg_ty = return_if_err!(self.typer.node_ty(arg.pat.id));
 239
 240             let arg_cmt = self.mc.cat_rvalue(
 241                 arg.id,
 242                 arg.pat.span,
 243                 ty::ReScope(body.id), // Args live only as long as the fn body.
 244                 arg_ty);
 245
 246             self.walk_pat(arg_cmt, &*arg.pat);
 247         }
 248     }
 249
 250     fn tcx(&self) -> &'t ty::ctxt<'tcx> {
 251         self.typer.tcx()
 252     }
 253
 254     fn delegate_consume(&mut self,
 255                         consume_id: ast::NodeId,
 256                         consume_span: Span,
 257                         cmt: mc::cmt) {
 258         let mode = copy_or_move(self.tcx(), cmt.ty, DirectRefMove);
 259         self.delegate.consume(consume_id, consume_span, cmt, mode);
 260     }
 261
 262     fn consume_exprs(&mut self, exprs: &Vec<P<ast::Expr>>) {
 263         for expr in exprs.iter() {
 264             self.consume_expr(&**expr);
 265         }
 266     }
 267
 268     fn consume_expr(&mut self, expr: &ast::Expr) {
 269         debug!("consume_expr(expr={})", expr.repr(self.tcx()));
 270
 271         let cmt = return_if_err!(self.mc.cat_expr(expr));
 272         self.delegate_consume(expr.id, expr.span, cmt);
 273         self.walk_expr(expr);
 274     }
 275
 276     fn mutate_expr(&mut self,
 277                    assignment_expr: &ast::Expr,
 278                    expr: &ast::Expr,
 279                    mode: MutateMode) {
 280         let cmt = return_if_err!(self.mc.cat_expr(expr));
 281         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 282         self.walk_expr(expr);
 283     }
 284
 285     fn borrow_expr(&mut self,
 286                    expr: &ast::Expr,
 287                    r: ty::Region,
 288                    bk: ty::BorrowKind,
 289                    cause: LoanCause) {
 290         debug!("borrow_expr(expr={}, r={}, bk={})",
 291                expr.repr(self.tcx()), r.repr(self.tcx()), bk.repr(self.tcx()));
 292
 293         let cmt = return_if_err!(self.mc.cat_expr(expr));
 294         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 295
 296         // Note: Unlike consume, we can ignore ExprParen. cat_expr
 297         // already skips over them, and walk will uncover any
 298         // attachments or whatever.
 299         self.walk_expr(expr)
 300     }
 301
 302     fn select_from_expr(&mut self, expr: &ast::Expr) {
 303         self.walk_expr(expr)
 304     }
 305
 306     pub fn walk_expr(&mut self, expr: &ast::Expr) {
 307         debug!("walk_expr(expr={})", expr.repr(self.tcx()));
 308
 309         self.walk_adjustment(expr);
 310
 311         match expr.node {
 312             ast::ExprParen(ref subexpr) => {
 313                 self.walk_expr(&**subexpr)
 314             }
 315
 316             ast::ExprPath(..) => { }
 317
 318             ast::ExprUnary(ast::UnDeref, ref base) => {      // *base
 319                 if !self.walk_overloaded_operator(expr, &**base, None) {
 320                     self.select_from_expr(&**base);
 321                 }
 322             }
 323
 324             ast::ExprField(ref base, _, _) => {         // base.f
 325                 self.select_from_expr(&**base);
 326             }
 327
 328             ast::ExprTupField(ref base, _, _) => {         // base.<n>
 329                 self.select_from_expr(&**base);
 330             }
 331
 332             ast::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 333                 if !self.walk_overloaded_operator(expr, &**lhs, Some(&**rhs)) {
 334                     self.select_from_expr(&**lhs);
 335                     self.consume_expr(&**rhs);
 336                 }
 337             }
 338
 339             ast::ExprCall(ref callee, ref args) => {    // callee(args)
 340                 self.walk_callee(expr, &**callee);
 341                 self.consume_exprs(args);
 342             }
 343
 344             ast::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 345                 self.consume_exprs(args);
 346             }
 347
 348             ast::ExprStruct(_, ref fields, ref opt_with) => {
 349                 self.walk_struct_expr(expr, fields, opt_with);
 350             }
 351
 352             ast::ExprTup(ref exprs) => {
 353                 self.consume_exprs(exprs);
 354             }
 355
 356             ast::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
 357                 self.consume_expr(&**cond_expr);
 358                 self.walk_block(&**then_blk);
 359                 for else_expr in opt_else_expr.iter() {
 360                     self.consume_expr(&**else_expr);
 361                 }
 362             }
 363
 364             ast::ExprMatch(ref discr, ref arms) => {
 365                 // treatment of the discriminant is handled while
 366                 // walking the arms:
 367                 self.walk_expr(&**discr);
 368                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
 369                 for arm in arms.iter() {
 370                     self.walk_arm(discr_cmt.clone(), arm);
 371                 }
 372             }
 373
 374             ast::ExprVec(ref exprs) => {
 375                 self.consume_exprs(exprs);
 376             }
 377
 378             ast::ExprAddrOf(m, ref base) => {   // &base
 379                 // make sure that the thing we are pointing out stays valid
 380                 // for the lifetime `scope_r` of the resulting ptr:
 381                 let expr_ty = ty::expr_ty(self.tcx(), expr);
 382                 if !ty::type_is_bot(expr_ty) {
 383                     let r = ty::ty_region(self.tcx(), expr.span, expr_ty);
 384                     let bk = ty::BorrowKind::from_mutbl(m);
 385                     self.borrow_expr(&**base, r, bk, AddrOf);
 386                 } else {
 387                     self.walk_expr(&**base);
 388                 }
 389             }
 390
 391             ast::ExprInlineAsm(ref ia) => {
 392                 for &(_, ref input) in ia.inputs.iter() {
 393                     self.consume_expr(&**input);
 394                 }
 395
 396                 for &(_, ref output, is_rw) in ia.outputs.iter() {
 397                     self.mutate_expr(expr, &**output,
 398                                            if is_rw { WriteAndRead } else { JustWrite });
 399                 }
 400             }
 401
 402             ast::ExprBreak(..) |
 403             ast::ExprAgain(..) |
 404             ast::ExprLit(..) => {}
 405
 406             ast::ExprLoop(ref blk, _) => {
 407                 self.walk_block(&**blk);
 408             }
 409
 410             ast::ExprWhile(ref cond_expr, ref blk, _) => {
 411                 self.consume_expr(&**cond_expr);
 412                 self.walk_block(&**blk);
 413             }
 414
 415             ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
 416                 // The pattern lives as long as the block.
 417                 debug!("walk_expr for loop case: blk id={}", blk.id);
 418                 self.consume_expr(&**head);
 419
 420                 // Fetch the type of the value that the iteration yields to
 421                 // produce the pattern's categorized mutable type.
 422                 let pattern_type = return_if_err!(self.typer.node_ty(pat.id));
 423                 let pat_cmt = self.mc.cat_rvalue(pat.id,
 424                                                  pat.span,
 425                                                  ty::ReScope(blk.id),
 426                                                  pattern_type);
 427                 self.walk_pat(pat_cmt, &**pat);
 428
 429                 self.walk_block(&**blk);
 430             }
 431
 432             ast::ExprUnary(_, ref lhs) => {
 433                 if !self.walk_overloaded_operator(expr, &**lhs, None) {
 434                     self.consume_expr(&**lhs);
 435                 }
 436             }
 437
 438             ast::ExprBinary(_, ref lhs, ref rhs) => {
 439                 if !self.walk_overloaded_operator(expr, &**lhs, Some(&**rhs)) {
 440                     self.consume_expr(&**lhs);
 441                     self.consume_expr(&**rhs);
 442                 }
 443             }
 444
 445             ast::ExprBlock(ref blk) => {
 446                 self.walk_block(&**blk);
 447             }
 448
 449             ast::ExprRet(ref opt_expr) => {
 450                 for expr in opt_expr.iter() {
 451                     self.consume_expr(&**expr);
 452                 }
 453             }
 454
 455             ast::ExprAssign(ref lhs, ref rhs) => {
 456                 self.mutate_expr(expr, &**lhs, JustWrite);
 457                 self.consume_expr(&**rhs);
 458             }
 459
 460             ast::ExprCast(ref base, _) => {
 461                 self.consume_expr(&**base);
 462             }
 463
 464             ast::ExprAssignOp(_, ref lhs, ref rhs) => {
 465                 // This will have to change if/when we support
 466                 // overloaded operators for `+=` and so forth.
 467                 self.mutate_expr(expr, &**lhs, WriteAndRead);
 468                 self.consume_expr(&**rhs);
 469             }
 470
 471             ast::ExprRepeat(ref base, ref count) => {
 472                 self.consume_expr(&**base);
 473                 self.consume_expr(&**count);
 474             }
 475
 476             ast::ExprFnBlock(..) |
 477             ast::ExprUnboxedFn(..) |
 478             ast::ExprProc(..) => {
 479                 self.walk_captures(expr)
 480             }
 481
 482             ast::ExprBox(ref place, ref base) => {
 483                 self.consume_expr(&**place);
 484                 self.consume_expr(&**base);
 485             }
 486
 487             ast::ExprMac(..) => {
 488                 self.tcx().sess.span_bug(
 489                     expr.span,
 490                     "macro expression remains after expansion");
 491             }
 492         }
 493     }
 494
 495     fn walk_callee(&mut self, call: &ast::Expr, callee: &ast::Expr) {
 496         let callee_ty = ty::expr_ty_adjusted(self.tcx(), callee);
 497         debug!("walk_callee: callee={} callee_ty={}",
 498                callee.repr(self.tcx()), callee_ty.repr(self.tcx()));
 499         match ty::get(callee_ty).sty {
 500             ty::ty_bare_fn(..) => {
 501                 self.consume_expr(callee);
 502             }
 503             ty::ty_closure(ref f) => {
 504                 match f.onceness {
 505                     ast::Many => {
 506                         self.borrow_expr(callee,
 507                                          ty::ReScope(call.id),
 508                                          ty::UniqueImmBorrow,
 509                                          ClosureInvocation);
 510                     }
 511                     ast::Once => {
 512                         self.consume_expr(callee);
 513                     }
 514                 }
 515             }
 516             _ => {
 517                 let overloaded_call_type =
 518                     match self.tcx()
 519                               .method_map
 520                               .borrow()
 521                               .find(&MethodCall::expr(call.id)) {
 522                     Some(ref method_callee) => {
 523                         OverloadedCallType::from_method_origin(
 524                             self.tcx(),
 525                             &method_callee.origin)
 526                     }
 527                     None => {
 528                         self.tcx().sess.span_bug(
 529                             callee.span,
 530                             format!("unexpected callee type {}",
 531                                     callee_ty.repr(self.tcx())).as_slice())
 532                     }
 533                 };
 534                 match overloaded_call_type {
 535                     FnMutOverloadedCall => {
 536                         self.borrow_expr(callee,
 537                                          ty::ReScope(call.id),
 538                                          ty::MutBorrow,
 539                                          ClosureInvocation);
 540                     }
 541                     FnOverloadedCall => {
 542                         self.borrow_expr(callee,
 543                                          ty::ReScope(call.id),
 544                                          ty::ImmBorrow,
 545                                          ClosureInvocation);
 546                     }
 547                     FnOnceOverloadedCall => self.consume_expr(callee),
 548                 }
 549             }
 550         }
 551     }
 552
 553     fn walk_stmt(&mut self, stmt: &ast::Stmt) {
 554         match stmt.node {
 555             ast::StmtDecl(ref decl, _) => {
 556                 match decl.node {
 557                     ast::DeclLocal(ref local) => {
 558                         self.walk_local(&**local);
 559                     }
 560
 561                     ast::DeclItem(_) => {
 562                         // we don't visit nested items in this visitor,
 563                         // only the fn body we were given.
 564                     }
 565                 }
 566             }
 567
 568             ast::StmtExpr(ref expr, _) |
 569             ast::StmtSemi(ref expr, _) => {
 570                 self.consume_expr(&**expr);
 571             }
 572
 573             ast::StmtMac(..) => {
 574                 self.tcx().sess.span_bug(stmt.span, "unexpanded stmt macro");
 575             }
 576         }
 577     }
 578
 579     fn walk_local(&mut self, local: &ast::Local) {
 580         match local.init {
 581             None => {
 582                 let delegate = &mut self.delegate;
 583                 pat_util::pat_bindings(&self.typer.tcx().def_map, &*local.pat,
 584                                        |_, id, span, _| {
 585                     delegate.decl_without_init(id, span);
 586                 })
 587             }
 588
 589             Some(ref expr) => {
 590                 // Variable declarations with
 591                 // initializers are considered
 592                 // "assigns", which is handled by
 593                 // `walk_pat`:
 594                 self.walk_expr(&**expr);
 595                 let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
 596                 self.walk_pat(init_cmt, &*local.pat);
 597             }
 598         }
 599     }
 600
 601     fn walk_block(&mut self, blk: &ast::Block) {
 602         /*!
 603          * Indicates that the value of `blk` will be consumed,
 604          * meaning either copied or moved depending on its type.
 605          */
 606
 607         debug!("walk_block(blk.id={:?})", blk.id);
 608
 609         for stmt in blk.stmts.iter() {
 610             self.walk_stmt(&**stmt);
 611         }
 612
 613         for tail_expr in blk.expr.iter() {
 614             self.consume_expr(&**tail_expr);
 615         }
 616     }
 617
 618     fn walk_struct_expr(&mut self,
 619                         _expr: &ast::Expr,
 620                         fields: &Vec<ast::Field>,
 621                         opt_with: &Option<P<ast::Expr>>) {
 622         // Consume the expressions supplying values for each field.
 623         for field in fields.iter() {
 624             self.consume_expr(&*field.expr);
 625         }
 626
 627         let with_expr = match *opt_with {
 628             Some(ref w) => &**w,
 629             None => { return; }
 630         };
 631
 632         let with_cmt = return_if_err!(self.mc.cat_expr(&*with_expr));
 633
 634         // Select just those fields of the `with`
 635         // expression that will actually be used
 636         let with_fields = match ty::get(with_cmt.ty).sty {
 637             ty::ty_struct(did, ref substs) => {
 638                 ty::struct_fields(self.tcx(), did, substs)
 639             }
 640             _ => {
 641                 self.tcx().sess.span_bug(
 642                     with_expr.span,
 643                     "with expression doesn't evaluate to a struct");
 644             }
 645         };
 646
 647         // Consume those fields of the with expression that are needed.
 648         for with_field in with_fields.iter() {
 649             if !contains_field_named(with_field, fields) {
 650                 let cmt_field = self.mc.cat_field(&*with_expr,
 651                                                   with_cmt.clone(),
 652                                                   with_field.ident,
 653                                                   with_field.mt.ty);
 654                 self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 655             }
 656         }
 657
 658         fn contains_field_named(field: &ty::field,
 659                                 fields: &Vec<ast::Field>)
 660                                 -> bool
 661         {
 662             fields.iter().any(
 663                 |f| f.ident.node.name == field.ident.name)
 664         }
 665     }
 666
 667     // Invoke the appropriate delegate calls for anything that gets
 668     // consumed or borrowed as part of the automatic adjustment
 669     // process.
 670     fn walk_adjustment(&mut self, expr: &ast::Expr) {
 671         let typer = self.typer;
 672         match typer.adjustments().borrow().find(&expr.id) {
 673             None => { }
 674             Some(adjustment) => {
 675                 match *adjustment {
 676                     ty::AutoAddEnv(..) => {
 677                         // Creating a closure consumes the input and stores it
 678                         // into the resulting rvalue.
 679                         debug!("walk_adjustment(AutoAddEnv)");
 680                         let cmt_unadjusted =
 681                             return_if_err!(self.mc.cat_expr_unadjusted(expr));
 682                         self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 683                     }
 684                     ty::AutoDerefRef(ty::AutoDerefRef {
 685                         autoref: ref opt_autoref,
 686                         autoderefs: n
 687                     }) => {
 688                         self.walk_autoderefs(expr, n);
 689
 690                         match *opt_autoref {
 691                             None => { }
 692                             Some(ref r) => {
 693                                 self.walk_autoref(expr, r, n);
 694                             }
 695                         }
 696                     }
 697                 }
 698             }
 699         }
 700     }
 701
 702     fn walk_autoderefs(&mut self,
 703                        expr: &ast::Expr,
 704                        autoderefs: uint) {
 705         /*!
 706          * Autoderefs for overloaded Deref calls in fact reference
 707          * their receiver. That is, if we have `(*x)` where `x` is of
 708          * type `Rc<T>`, then this in fact is equivalent to
 709          * `x.deref()`. Since `deref()` is declared with `&self`, this
 710          * is an autoref of `x`.
 711          */
 712         debug!("walk_autoderefs expr={} autoderefs={}", expr.repr(self.tcx()), autoderefs);
 713
 714         for i in range(0, autoderefs) {
 715             let deref_id = typeck::MethodCall::autoderef(expr.id, i);
 716             match self.typer.node_method_ty(deref_id) {
 717                 None => {}
 718                 Some(method_ty) => {
 719                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 720                     let self_ty = *ty::ty_fn_args(method_ty).get(0);
 721                     let (m, r) = match ty::get(self_ty).sty {
 722                         ty::ty_rptr(r, ref m) => (m.mutbl, r),
 723                         _ => self.tcx().sess.span_bug(expr.span,
 724                                 format!("bad overloaded deref type {}",
 725                                     method_ty.repr(self.tcx())).as_slice())
 726                     };
 727                     let bk = ty::BorrowKind::from_mutbl(m);
 728                     self.delegate.borrow(expr.id, expr.span, cmt,
 729                                          r, bk, AutoRef);
 730                 }
 731             }
 732         }
 733     }
 734
 735     fn walk_autoref(&mut self,
 736                     expr: &ast::Expr,
 737                     autoref: &ty::AutoRef,
 738                     n: uint) {
 739         debug!("walk_autoref expr={}", expr.repr(self.tcx()));
 740
 741         // Match for unique trait coercions first, since we don't need the
 742         // call to cat_expr_autoderefd.
 743         match *autoref {
 744             ty::AutoUnsizeUniq(ty::UnsizeVtable(..)) |
 745             ty::AutoUnsize(ty::UnsizeVtable(..)) => {
 746                 assert!(n == 1, format!("Expected exactly 1 deref with Uniq \
 747                                          AutoRefs, found: {}", n));
 748                 let cmt_unadjusted =
 749                     return_if_err!(self.mc.cat_expr_unadjusted(expr));
 750                 self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 751                 return;
 752             }
 753             _ => {}
 754         }
 755
 756         let cmt_derefd = return_if_err!(
 757             self.mc.cat_expr_autoderefd(expr, n));
 758         debug!("walk_adjustment: cmt_derefd={}",
 759                cmt_derefd.repr(self.tcx()));
 760
 761         match *autoref {
 762             ty::AutoPtr(r, m, _) => {
 763                 self.delegate.borrow(expr.id,
 764                                      expr.span,
 765                                      cmt_derefd,
 766                                      r,
 767                                      ty::BorrowKind::from_mutbl(m),
 768                                      AutoRef);
 769             }
 770             ty::AutoUnsizeUniq(_) | ty::AutoUnsize(_) | ty::AutoUnsafe(..) => {}
 771         }
 772     }
 773
 774     fn walk_overloaded_operator(&mut self,
 775                                 expr: &ast::Expr,
 776                                 receiver: &ast::Expr,
 777                                 rhs: Option<&ast::Expr>)
 778                                 -> bool
 779     {
 780         if !self.typer.is_method_call(expr.id) {
 781             return false;
 782         }
 783
 784         self.walk_expr(receiver);
 785
 786         // Arguments (but not receivers) to overloaded operator
 787         // methods are implicitly autoref'd which sadly does not use
 788         // adjustments, so we must hardcode the borrow here.
 789
 790         let r = ty::ReScope(expr.id);
 791         let bk = ty::ImmBorrow;
 792
 793         for &arg in rhs.iter() {
 794             self.borrow_expr(arg, r, bk, OverloadedOperator);
 795         }
 796         return true;
 797     }
 798
 799     fn walk_arm(&mut self, discr_cmt: mc::cmt, arm: &ast::Arm) {
 800         for pat in arm.pats.iter() {
 801             self.walk_pat(discr_cmt.clone(), &**pat);
 802         }
 803
 804         for guard in arm.guard.iter() {
 805             self.consume_expr(&**guard);
 806         }
 807
 808         self.consume_expr(&*arm.body);
 809     }
 810
 811     fn walk_pat(&mut self, cmt_discr: mc::cmt, pat: &ast::Pat) {
 812         debug!("walk_pat cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
 813                pat.repr(self.tcx()));
 814         let mc = &self.mc;
 815         let typer = self.typer;
 816         let tcx = typer.tcx();
 817         let def_map = &self.typer.tcx().def_map;
 818         let delegate = &mut self.delegate;
 819         return_if_err!(mc.cat_pattern(cmt_discr, &*pat, |mc, cmt_pat, pat| {
 820             if pat_util::pat_is_binding(def_map, pat) {
 821                 let tcx = typer.tcx();
 822
 823                 debug!("binding cmt_pat={} pat={}",
 824                        cmt_pat.repr(tcx),
 825                        pat.repr(tcx));
 826
 827                 // pat_ty: the type of the binding being produced.
 828                 let pat_ty = return_if_err!(typer.node_ty(pat.id));
 829
 830                 // Each match binding is effectively an assignment to the
 831                 // binding being produced.
 832                 let def = def_map.borrow().get_copy(&pat.id);
 833                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
 834                     Ok(binding_cmt) => {
 835                         delegate.mutate(pat.id, pat.span, binding_cmt, Init);
 836                     }
 837                     Err(_) => { }
 838                 }
 839
 840                 // It is also a borrow or copy/move of the value being matched.
 841                 match pat.node {
 842                     ast::PatIdent(ast::BindByRef(m), _, _) => {
 843                         let (r, bk) = {
 844                             (ty::ty_region(tcx, pat.span, pat_ty),
 845                              ty::BorrowKind::from_mutbl(m))
 846                         };
 847                         delegate.borrow(pat.id, pat.span, cmt_pat,
 848                                              r, bk, RefBinding);
 849                     }
 850                     ast::PatIdent(ast::BindByValue(_), _, _) => {
 851                         let mode = copy_or_move(typer.tcx(), cmt_pat.ty, PatBindingMove);
 852                         debug!("walk_pat binding consuming pat");
 853                         delegate.consume_pat(pat, cmt_pat, mode);
 854                     }
 855                     _ => {
 856                         typer.tcx().sess.span_bug(
 857                             pat.span,
 858                             "binding pattern not an identifier");
 859                     }
 860                 }
 861             } else {
 862                 match pat.node {
 863                     ast::PatVec(_, Some(ref slice_pat), _) => {
 864                         // The `slice_pat` here creates a slice into
 865                         // the original vector.  This is effectively a
 866                         // borrow of the elements of the vector being
 867                         // matched.
 868
 869                         let (slice_cmt, slice_mutbl, slice_r) = {
 870                             match mc.cat_slice_pattern(cmt_pat, &**slice_pat) {
 871                                 Ok(v) => v,
 872                                 Err(()) => {
 873                                     tcx.sess.span_bug(slice_pat.span,
 874                                                       "Err from mc")
 875                                 }
 876                             }
 877                         };
 878
 879                         // Note: We declare here that the borrow
 880                         // occurs upon entering the `[...]`
 881                         // pattern. This implies that something like
 882                         // `[a, ..b]` where `a` is a move is illegal,
 883                         // because the borrow is already in effect.
 884                         // In fact such a move would be safe-ish, but
 885                         // it effectively *requires* that we use the
 886                         // nulling out semantics to indicate when a
 887                         // value has been moved, which we are trying
 888                         // to move away from.  Otherwise, how can we
 889                         // indicate that the first element in the
 890                         // vector has been moved?  Eventually, we
 891                         // could perhaps modify this rule to permit
 892                         // `[..a, b]` where `b` is a move, because in
 893                         // that case we can adjust the length of the
 894                         // original vec accordingly, but we'd have to
 895                         // make trans do the right thing, and it would
 896                         // only work for `~` vectors. It seems simpler
 897                         // to just require that people call
 898                         // `vec.pop()` or `vec.unshift()`.
 899                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
 900                         delegate.borrow(pat.id, pat.span,
 901                                         slice_cmt, slice_r,
 902                                         slice_bk, RefBinding);
 903                     }
 904                     _ => { }
 905                 }
 906             }
 907         }));
 908     }
 909
 910     fn walk_captures(&mut self, closure_expr: &ast::Expr) {
 911         debug!("walk_captures({})", closure_expr.repr(self.tcx()));
 912
 913         let tcx = self.typer.tcx();
 914         ty::with_freevars(tcx, closure_expr.id, |freevars| {
 915             match self.tcx().capture_mode(closure_expr.id) {
 916                 ast::CaptureByRef => {
 917                     self.walk_by_ref_captures(closure_expr, freevars);
 918                 }
 919                 ast::CaptureByValue => {
 920                     self.walk_by_value_captures(closure_expr, freevars);
 921                 }
 922             }
 923         });
 924     }
 925
 926     fn walk_by_ref_captures(&mut self,
 927                             closure_expr: &ast::Expr,
 928                             freevars: &[ty::Freevar]) {
 929         for freevar in freevars.iter() {
 930             let id_var = freevar.def.def_id().node;
 931             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 932                                                                closure_expr.span,
 933                                                                freevar.def));
 934
 935             // Lookup the kind of borrow the callee requires, as
 936             // inferred by regionbk
 937             let upvar_id = ty::UpvarId { var_id: id_var,
 938                                          closure_expr_id: closure_expr.id };
 939             let upvar_borrow = self.tcx().upvar_borrow_map.borrow()
 940                                    .get_copy(&upvar_id);
 941
 942             self.delegate.borrow(closure_expr.id,
 943                                  closure_expr.span,
 944                                  cmt_var,
 945                                  upvar_borrow.region,
 946                                  upvar_borrow.kind,
 947                                  ClosureCapture(freevar.span));
 948         }
 949     }
 950
 951     fn walk_by_value_captures(&mut self,
 952                               closure_expr: &ast::Expr,
 953                               freevars: &[ty::Freevar]) {
 954         for freevar in freevars.iter() {
 955             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 956                                                                closure_expr.span,
 957                                                                freevar.def));
 958             let mode = copy_or_move(self.tcx(), cmt_var.ty, CaptureMove);
 959             self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 960         }
 961     }
 962
 963     fn cat_captured_var(&mut self,
 964                         closure_id: ast::NodeId,
 965                         closure_span: Span,
 966                         upvar_def: def::Def)
 967                         -> mc::McResult<mc::cmt> {
 968         // Create the cmt for the variable being borrowed, from the
 969         // caller's perspective
 970         let var_id = upvar_def.def_id().node;
 971         let var_ty = try!(self.typer.node_ty(var_id));
 972         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 973     }
 974 }
 975
 976 fn copy_or_move(tcx: &ty::ctxt, ty: ty::t, move_reason: MoveReason) -> ConsumeMode {
 977     if ty::type_moves_by_default(tcx, ty) { Move(move_reason) } else { Copy }
 978 }
 979