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::LoanCause::*;
  16 pub use self::ConsumeMode::*;
  17 pub use self::MoveReason::*;
  18 pub use self::MatchMode::*;
  19 use self::TrackMatchMode::*;
  20 use self::OverloadedCallType::*;
  21
  22 use hir::def::Def;
  23 use hir::def_id::{DefId};
  24 use infer::InferCtxt;
  25 use middle::mem_categorization as mc;
  26 use ty::{self, TyCtxt, adjustment};
  27
  28 use hir::{self, PatKind};
  29
  30 use syntax::ast;
  31 use syntax::ptr::P;
  32 use syntax_pos::Span;
  33
  34 ///////////////////////////////////////////////////////////////////////////
  35 // The Delegate trait
  36
  37 /// This trait defines the callbacks you can expect to receive when
  38 /// employing the ExprUseVisitor.
  39 pub trait Delegate<'tcx> {
  40     // The value found at `cmt` is either copied or moved, depending
  41     // on mode.
  42     fn consume(&mut self,
  43                consume_id: ast::NodeId,
  44                consume_span: Span,
  45                cmt: mc::cmt<'tcx>,
  46                mode: ConsumeMode);
  47
  48     // The value found at `cmt` has been determined to match the
  49     // pattern binding `matched_pat`, and its subparts are being
  50     // copied or moved depending on `mode`.  Note that `matched_pat`
  51     // is called on all variant/structs in the pattern (i.e., the
  52     // interior nodes of the pattern's tree structure) while
  53     // consume_pat is called on the binding identifiers in the pattern
  54     // (which are leaves of the pattern's tree structure).
  55     //
  56     // Note that variants/structs and identifiers are disjoint; thus
  57     // `matched_pat` and `consume_pat` are never both called on the
  58     // same input pattern structure (though of `consume_pat` can be
  59     // called on a subpart of an input passed to `matched_pat).
  60     fn matched_pat(&mut self,
  61                    matched_pat: &hir::Pat,
  62                    cmt: mc::cmt<'tcx>,
  63                    mode: MatchMode);
  64
  65     // The value found at `cmt` is either copied or moved via the
  66     // pattern binding `consume_pat`, depending on mode.
  67     fn consume_pat(&mut self,
  68                    consume_pat: &hir::Pat,
  69                    cmt: mc::cmt<'tcx>,
  70                    mode: ConsumeMode);
  71
  72     // The value found at `borrow` is being borrowed at the point
  73     // `borrow_id` for the region `loan_region` with kind `bk`.
  74     fn borrow(&mut self,
  75               borrow_id: ast::NodeId,
  76               borrow_span: Span,
  77               cmt: mc::cmt<'tcx>,
  78               loan_region: &'tcx ty::Region,
  79               bk: ty::BorrowKind,
  80               loan_cause: LoanCause);
  81
  82     // The local variable `id` is declared but not initialized.
  83     fn decl_without_init(&mut self,
  84                          id: ast::NodeId,
  85                          span: Span);
  86
  87     // The path at `cmt` is being assigned to.
  88     fn mutate(&mut self,
  89               assignment_id: ast::NodeId,
  90               assignment_span: Span,
  91               assignee_cmt: mc::cmt<'tcx>,
  92               mode: MutateMode);
  93 }
  94
  95 #[derive(Copy, Clone, PartialEq, Debug)]
  96 pub enum LoanCause {
  97     ClosureCapture(Span),
  98     AddrOf,
  99     AutoRef,
 100     AutoUnsafe,
 101     RefBinding,
 102     OverloadedOperator,
 103     ClosureInvocation,
 104     ForLoop,
 105     MatchDiscriminant
 106 }
 107
 108 #[derive(Copy, Clone, PartialEq, Debug)]
 109 pub enum ConsumeMode {
 110     Copy,                // reference to x where x has a type that copies
 111     Move(MoveReason),    // reference to x where x has a type that moves
 112 }
 113
 114 #[derive(Copy, Clone, PartialEq, Debug)]
 115 pub enum MoveReason {
 116     DirectRefMove,
 117     PatBindingMove,
 118     CaptureMove,
 119 }
 120
 121 #[derive(Copy, Clone, PartialEq, Debug)]
 122 pub enum MatchMode {
 123     NonBindingMatch,
 124     BorrowingMatch,
 125     CopyingMatch,
 126     MovingMatch,
 127 }
 128
 129 #[derive(Copy, Clone, PartialEq, Debug)]
 130 enum TrackMatchMode {
 131     Unknown,
 132     Definite(MatchMode),
 133     Conflicting,
 134 }
 135
 136 impl TrackMatchMode {
 137     // Builds up the whole match mode for a pattern from its constituent
 138     // parts.  The lattice looks like this:
 139     //
 140     //          Conflicting
 141     //            /     \
 142     //           /       \
 143     //      Borrowing   Moving
 144     //           \       /
 145     //            \     /
 146     //            Copying
 147     //               |
 148     //          NonBinding
 149     //               |
 150     //            Unknown
 151     //
 152     // examples:
 153     //
 154     // * `(_, some_int)` pattern is Copying, since
 155     //   NonBinding + Copying => Copying
 156     //
 157     // * `(some_int, some_box)` pattern is Moving, since
 158     //   Copying + Moving => Moving
 159     //
 160     // * `(ref x, some_box)` pattern is Conflicting, since
 161     //   Borrowing + Moving => Conflicting
 162     //
 163     // Note that the `Unknown` and `Conflicting` states are
 164     // represented separately from the other more interesting
 165     // `Definite` states, which simplifies logic here somewhat.
 166     fn lub(&mut self, mode: MatchMode) {
 167         *self = match (*self, mode) {
 168             // Note that clause order below is very significant.
 169             (Unknown, new) => Definite(new),
 170             (Definite(old), new) if old == new => Definite(old),
 171
 172             (Definite(old), NonBindingMatch) => Definite(old),
 173             (Definite(NonBindingMatch), new) => Definite(new),
 174
 175             (Definite(old), CopyingMatch) => Definite(old),
 176             (Definite(CopyingMatch), new) => Definite(new),
 177
 178             (Definite(_), _) => Conflicting,
 179             (Conflicting, _) => *self,
 180         };
 181     }
 182
 183     fn match_mode(&self) -> MatchMode {
 184         match *self {
 185             Unknown => NonBindingMatch,
 186             Definite(mode) => mode,
 187             Conflicting => {
 188                 // Conservatively return MovingMatch to let the
 189                 // compiler continue to make progress.
 190                 MovingMatch
 191             }
 192         }
 193     }
 194 }
 195
 196 #[derive(Copy, Clone, PartialEq, Debug)]
 197 pub enum MutateMode {
 198     Init,
 199     JustWrite,    // x = y
 200     WriteAndRead, // x += y
 201 }
 202
 203 #[derive(Copy, Clone)]
 204 enum OverloadedCallType {
 205     FnOverloadedCall,
 206     FnMutOverloadedCall,
 207     FnOnceOverloadedCall,
 208 }
 209
 210 impl OverloadedCallType {
 211     fn from_trait_id(tcx: TyCtxt, trait_id: DefId) -> OverloadedCallType {
 212         for &(maybe_function_trait, overloaded_call_type) in &[
 213             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 214             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 215             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 216         ] {
 217             match maybe_function_trait {
 218                 Some(function_trait) if function_trait == trait_id => {
 219                     return overloaded_call_type
 220                 }
 221                 _ => continue,
 222             }
 223         }
 224
 225         bug!("overloaded call didn't map to known function trait")
 226     }
 227
 228     fn from_method_id(tcx: TyCtxt, method_id: DefId) -> OverloadedCallType {
 229         let method = tcx.associated_item(method_id);
 230         OverloadedCallType::from_trait_id(tcx, method.container.id())
 231     }
 232 }
 233
 234 ///////////////////////////////////////////////////////////////////////////
 235 // The ExprUseVisitor type
 236 //
 237 // This is the code that actually walks the tree. Like
 238 // mem_categorization, it requires a TYPER, which is a type that
 239 // supplies types from the tree. After type checking is complete, you
 240 // can just use the tcx as the typer.
 241 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 242     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 243     delegate: &'a mut Delegate<'tcx>,
 244 }
 245
 246 // If the TYPER results in an error, it's because the type check
 247 // failed (or will fail, when the error is uncovered and reported
 248 // during writeback). In this case, we just ignore this part of the
 249 // code.
 250 //
 251 // Note that this macro appears similar to try!(), but, unlike try!(),
 252 // it does not propagate the error.
 253 macro_rules! return_if_err {
 254     ($inp: expr) => (
 255         match $inp {
 256             Ok(v) => v,
 257             Err(()) => {
 258                 debug!("mc reported err");
 259                 return
 260             }
 261         }
 262     )
 263 }
 264
 265 /// Whether the elements of an overloaded operation are passed by value or by reference
 266 enum PassArgs {
 267     ByValue,
 268     ByRef,
 269 }
 270
 271 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 272     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 273                infcx: &'a InferCtxt<'a, 'gcx, 'tcx>)
 274                -> Self
 275     {
 276         ExprUseVisitor::with_options(delegate, infcx, mc::MemCategorizationOptions::default())
 277     }
 278
 279     pub fn with_options(delegate: &'a mut (Delegate<'tcx>+'a),
 280                         infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 281                         options: mc::MemCategorizationOptions)
 282                -> Self
 283     {
 284         ExprUseVisitor {
 285             mc: mc::MemCategorizationContext::with_options(infcx, options),
 286             delegate: delegate
 287         }
 288     }
 289
 290     pub fn consume_body(&mut self, body: &hir::Body) {
 291         debug!("consume_body(body={:?})", body);
 292
 293         for arg in &body.arguments {
 294             let arg_ty = return_if_err!(self.mc.infcx.node_ty(arg.pat.id));
 295
 296             let fn_body_scope_r = self.tcx().node_scope_region(body.value.id);
 297             let arg_cmt = self.mc.cat_rvalue(
 298                 arg.id,
 299                 arg.pat.span,
 300                 fn_body_scope_r, // Args live only as long as the fn body.
 301                 fn_body_scope_r,
 302                 arg_ty);
 303
 304             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 305         }
 306
 307         self.consume_expr(&body.value);
 308     }
 309
 310     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 311         self.mc.infcx.tcx
 312     }
 313
 314     fn delegate_consume(&mut self,
 315                         consume_id: ast::NodeId,
 316                         consume_span: Span,
 317                         cmt: mc::cmt<'tcx>) {
 318         debug!("delegate_consume(consume_id={}, cmt={:?})",
 319                consume_id, cmt);
 320
 321         let mode = copy_or_move(self.mc.infcx, &cmt, DirectRefMove);
 322         self.delegate.consume(consume_id, consume_span, cmt, mode);
 323     }
 324
 325     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 326         for expr in exprs {
 327             self.consume_expr(&expr);
 328         }
 329     }
 330
 331     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 332         debug!("consume_expr(expr={:?})", expr);
 333
 334         let cmt = return_if_err!(self.mc.cat_expr(expr));
 335         self.delegate_consume(expr.id, expr.span, cmt);
 336         self.walk_expr(expr);
 337     }
 338
 339     fn mutate_expr(&mut self,
 340                    assignment_expr: &hir::Expr,
 341                    expr: &hir::Expr,
 342                    mode: MutateMode) {
 343         let cmt = return_if_err!(self.mc.cat_expr(expr));
 344         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 345         self.walk_expr(expr);
 346     }
 347
 348     fn borrow_expr(&mut self,
 349                    expr: &hir::Expr,
 350                    r: &'tcx ty::Region,
 351                    bk: ty::BorrowKind,
 352                    cause: LoanCause) {
 353         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 354                expr, r, bk);
 355
 356         let cmt = return_if_err!(self.mc.cat_expr(expr));
 357         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 358
 359         self.walk_expr(expr)
 360     }
 361
 362     fn select_from_expr(&mut self, expr: &hir::Expr) {
 363         self.walk_expr(expr)
 364     }
 365
 366     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 367         debug!("walk_expr(expr={:?})", expr);
 368
 369         self.walk_adjustment(expr);
 370
 371         match expr.node {
 372             hir::ExprPath(_) => { }
 373
 374             hir::ExprType(ref subexpr, _) => {
 375                 self.walk_expr(&subexpr)
 376             }
 377
 378             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 379                 if !self.walk_overloaded_operator(expr, &base, Vec::new(), PassArgs::ByRef) {
 380                     self.select_from_expr(&base);
 381                 }
 382             }
 383
 384             hir::ExprField(ref base, _) => {         // base.f
 385                 self.select_from_expr(&base);
 386             }
 387
 388             hir::ExprTupField(ref base, _) => {         // base.<n>
 389                 self.select_from_expr(&base);
 390             }
 391
 392             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 393                 if !self.walk_overloaded_operator(expr,
 394                                                   &lhs,
 395                                                   vec![&rhs],
 396                                                   PassArgs::ByValue) {
 397                     self.select_from_expr(&lhs);
 398                     self.consume_expr(&rhs);
 399                 }
 400             }
 401
 402             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 403                 self.walk_callee(expr, &callee);
 404                 self.consume_exprs(args);
 405             }
 406
 407             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 408                 self.consume_exprs(args);
 409             }
 410
 411             hir::ExprStruct(_, ref fields, ref opt_with) => {
 412                 self.walk_struct_expr(fields, opt_with);
 413             }
 414
 415             hir::ExprTup(ref exprs) => {
 416                 self.consume_exprs(exprs);
 417             }
 418
 419             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 420                 self.consume_expr(&cond_expr);
 421                 self.walk_expr(&then_expr);
 422                 if let Some(ref else_expr) = *opt_else_expr {
 423                     self.consume_expr(&else_expr);
 424                 }
 425             }
 426
 427             hir::ExprMatch(ref discr, ref arms, _) => {
 428                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 429                 let r = self.tcx().types.re_empty;
 430                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 431
 432                 // treatment of the discriminant is handled while walking the arms.
 433                 for arm in arms {
 434                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 435                     let mode = mode.match_mode();
 436                     self.walk_arm(discr_cmt.clone(), arm, mode);
 437                 }
 438             }
 439
 440             hir::ExprArray(ref exprs) => {
 441                 self.consume_exprs(exprs);
 442             }
 443
 444             hir::ExprAddrOf(m, ref base) => {   // &base
 445                 // make sure that the thing we are pointing out stays valid
 446                 // for the lifetime `scope_r` of the resulting ptr:
 447                 let expr_ty = return_if_err!(self.mc.infcx.node_ty(expr.id));
 448                 if let ty::TyRef(r, _) = expr_ty.sty {
 449                     let bk = ty::BorrowKind::from_mutbl(m);
 450                     self.borrow_expr(&base, r, bk, AddrOf);
 451                 }
 452             }
 453
 454             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 455                 for (o, output) in ia.outputs.iter().zip(outputs) {
 456                     if o.is_indirect {
 457                         self.consume_expr(output);
 458                     } else {
 459                         self.mutate_expr(expr, output,
 460                                          if o.is_rw {
 461                                              MutateMode::WriteAndRead
 462                                          } else {
 463                                              MutateMode::JustWrite
 464                                          });
 465                     }
 466                 }
 467                 self.consume_exprs(inputs);
 468             }
 469
 470             hir::ExprAgain(..) |
 471             hir::ExprLit(..) => {}
 472
 473             hir::ExprLoop(ref blk, _, _) => {
 474                 self.walk_block(&blk);
 475             }
 476
 477             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 478                 self.consume_expr(&cond_expr);
 479                 self.walk_block(&blk);
 480             }
 481
 482             hir::ExprUnary(op, ref lhs) => {
 483                 let pass_args = if op.is_by_value() {
 484                     PassArgs::ByValue
 485                 } else {
 486                     PassArgs::ByRef
 487                 };
 488
 489                 if !self.walk_overloaded_operator(expr, &lhs, Vec::new(), pass_args) {
 490                     self.consume_expr(&lhs);
 491                 }
 492             }
 493
 494             hir::ExprBinary(op, ref lhs, ref rhs) => {
 495                 let pass_args = if op.node.is_by_value() {
 496                     PassArgs::ByValue
 497                 } else {
 498                     PassArgs::ByRef
 499                 };
 500
 501                 if !self.walk_overloaded_operator(expr, &lhs, vec![&rhs], pass_args) {
 502                     self.consume_expr(&lhs);
 503                     self.consume_expr(&rhs);
 504                 }
 505             }
 506
 507             hir::ExprBlock(ref blk) => {
 508                 self.walk_block(&blk);
 509             }
 510
 511             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 512                 if let Some(ref expr) = *opt_expr {
 513                     self.consume_expr(&expr);
 514                 }
 515             }
 516
 517             hir::ExprAssign(ref lhs, ref rhs) => {
 518                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 519                 self.consume_expr(&rhs);
 520             }
 521
 522             hir::ExprCast(ref base, _) => {
 523                 self.consume_expr(&base);
 524             }
 525
 526             hir::ExprAssignOp(op, ref lhs, ref rhs) => {
 527                 // NB All our assignment operations take the RHS by value
 528                 assert!(op.node.is_by_value());
 529
 530                 if !self.walk_overloaded_operator(expr, lhs, vec![rhs], PassArgs::ByValue) {
 531                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 532                     self.consume_expr(&rhs);
 533                 }
 534             }
 535
 536             hir::ExprRepeat(ref base, _) => {
 537                 self.consume_expr(&base);
 538             }
 539
 540             hir::ExprClosure(.., fn_decl_span) => {
 541                 self.walk_captures(expr, fn_decl_span)
 542             }
 543
 544             hir::ExprBox(ref base) => {
 545                 self.consume_expr(&base);
 546             }
 547         }
 548     }
 549
 550     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 551         let callee_ty = return_if_err!(self.mc.infcx.expr_ty_adjusted(callee));
 552         debug!("walk_callee: callee={:?} callee_ty={:?}",
 553                callee, callee_ty);
 554         match callee_ty.sty {
 555             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 556                 self.consume_expr(callee);
 557             }
 558             ty::TyError => { }
 559             _ => {
 560                 let overloaded_call_type =
 561                     match self.mc.infcx.node_method_id(ty::MethodCall::expr(call.id)) {
 562                         Some(method_id) => {
 563                             OverloadedCallType::from_method_id(self.tcx(), method_id)
 564                         }
 565                         None => {
 566                             span_bug!(
 567                                 callee.span,
 568                                 "unexpected callee type {}",
 569                                 callee_ty)
 570                         }
 571                     };
 572                 match overloaded_call_type {
 573                     FnMutOverloadedCall => {
 574                         let call_scope_r = self.tcx().node_scope_region(call.id);
 575                         self.borrow_expr(callee,
 576                                          call_scope_r,
 577                                          ty::MutBorrow,
 578                                          ClosureInvocation);
 579                     }
 580                     FnOverloadedCall => {
 581                         let call_scope_r = self.tcx().node_scope_region(call.id);
 582                         self.borrow_expr(callee,
 583                                          call_scope_r,
 584                                          ty::ImmBorrow,
 585                                          ClosureInvocation);
 586                     }
 587                     FnOnceOverloadedCall => self.consume_expr(callee),
 588                 }
 589             }
 590         }
 591     }
 592
 593     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 594         match stmt.node {
 595             hir::StmtDecl(ref decl, _) => {
 596                 match decl.node {
 597                     hir::DeclLocal(ref local) => {
 598                         self.walk_local(&local);
 599                     }
 600
 601                     hir::DeclItem(_) => {
 602                         // we don't visit nested items in this visitor,
 603                         // only the fn body we were given.
 604                     }
 605                 }
 606             }
 607
 608             hir::StmtExpr(ref expr, _) |
 609             hir::StmtSemi(ref expr, _) => {
 610                 self.consume_expr(&expr);
 611             }
 612         }
 613     }
 614
 615     fn walk_local(&mut self, local: &hir::Local) {
 616         match local.init {
 617             None => {
 618                 let delegate = &mut self.delegate;
 619                 local.pat.each_binding(|_, id, span, _| {
 620                     delegate.decl_without_init(id, span);
 621                 })
 622             }
 623
 624             Some(ref expr) => {
 625                 // Variable declarations with
 626                 // initializers are considered
 627                 // "assigns", which is handled by
 628                 // `walk_pat`:
 629                 self.walk_expr(&expr);
 630                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 631                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 632             }
 633         }
 634     }
 635
 636     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 637     /// depending on its type.
 638     fn walk_block(&mut self, blk: &hir::Block) {
 639         debug!("walk_block(blk.id={})", blk.id);
 640
 641         for stmt in &blk.stmts {
 642             self.walk_stmt(stmt);
 643         }
 644
 645         if let Some(ref tail_expr) = blk.expr {
 646             self.consume_expr(&tail_expr);
 647         }
 648     }
 649
 650     fn walk_struct_expr(&mut self,
 651                         fields: &[hir::Field],
 652                         opt_with: &Option<P<hir::Expr>>) {
 653         // Consume the expressions supplying values for each field.
 654         for field in fields {
 655             self.consume_expr(&field.expr);
 656         }
 657
 658         let with_expr = match *opt_with {
 659             Some(ref w) => &**w,
 660             None => { return; }
 661         };
 662
 663         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 664
 665         // Select just those fields of the `with`
 666         // expression that will actually be used
 667         match with_cmt.ty.sty {
 668             ty::TyAdt(adt, substs) if adt.is_struct() => {
 669                 // Consume those fields of the with expression that are needed.
 670                 for with_field in &adt.struct_variant().fields {
 671                     if !contains_field_named(with_field, fields) {
 672                         let cmt_field = self.mc.cat_field(
 673                             &*with_expr,
 674                             with_cmt.clone(),
 675                             with_field.name,
 676                             with_field.ty(self.tcx(), substs)
 677                         );
 678                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 679                     }
 680                 }
 681             }
 682             _ => {
 683                 // the base expression should always evaluate to a
 684                 // struct; however, when EUV is run during typeck, it
 685                 // may not. This will generate an error earlier in typeck,
 686                 // so we can just ignore it.
 687                 if !self.tcx().sess.has_errors() {
 688                     span_bug!(
 689                         with_expr.span,
 690                         "with expression doesn't evaluate to a struct");
 691                 }
 692             }
 693         }
 694
 695         // walk the with expression so that complex expressions
 696         // are properly handled.
 697         self.walk_expr(with_expr);
 698
 699         fn contains_field_named(field: &ty::FieldDef,
 700                                 fields: &[hir::Field])
 701                                 -> bool
 702         {
 703             fields.iter().any(
 704                 |f| f.name.node == field.name)
 705         }
 706     }
 707
 708     // Invoke the appropriate delegate calls for anything that gets
 709     // consumed or borrowed as part of the automatic adjustment
 710     // process.
 711     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 712         let infcx = self.mc.infcx;
 713         //NOTE(@jroesch): mixed RefCell borrow causes crash
 714         let adj = infcx.tables.borrow().adjustments.get(&expr.id).map(|x| x.clone());
 715         if let Some(adjustment) = adj {
 716             match adjustment.kind {
 717                 adjustment::Adjust::NeverToAny |
 718                 adjustment::Adjust::ReifyFnPointer |
 719                 adjustment::Adjust::UnsafeFnPointer |
 720                 adjustment::Adjust::ClosureFnPointer |
 721                 adjustment::Adjust::MutToConstPointer => {
 722                     // Creating a closure/fn-pointer or unsizing consumes
 723                     // the input and stores it into the resulting rvalue.
 724                     debug!("walk_adjustment: trivial adjustment");
 725                     let cmt_unadjusted =
 726                         return_if_err!(self.mc.cat_expr_unadjusted(expr));
 727                     self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 728                 }
 729                 adjustment::Adjust::DerefRef { autoderefs, autoref, unsize } => {
 730                     debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 731
 732                     self.walk_autoderefs(expr, autoderefs);
 733
 734                     let cmt_derefd =
 735                         return_if_err!(self.mc.cat_expr_autoderefd(expr, autoderefs));
 736
 737                     let cmt_refd =
 738                         self.walk_autoref(expr, cmt_derefd, autoref);
 739
 740                     if unsize {
 741                         // Unsizing consumes the thin pointer and produces a fat one.
 742                         self.delegate_consume(expr.id, expr.span, cmt_refd);
 743                     }
 744                 }
 745             }
 746         }
 747     }
 748
 749     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 750     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 751     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 752     fn walk_autoderefs(&mut self,
 753                        expr: &hir::Expr,
 754                        autoderefs: usize) {
 755         debug!("walk_autoderefs expr={:?} autoderefs={}", expr, autoderefs);
 756
 757         for i in 0..autoderefs {
 758             let deref_id = ty::MethodCall::autoderef(expr.id, i as u32);
 759             if let Some(method_ty) = self.mc.infcx.node_method_ty(deref_id) {
 760                 let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 761
 762                 // the method call infrastructure should have
 763                 // replaced all late-bound regions with variables:
 764                 let self_ty = method_ty.fn_sig().input(0);
 765                 let self_ty = self.tcx().no_late_bound_regions(&self_ty).unwrap();
 766
 767                 let (m, r) = match self_ty.sty {
 768                     ty::TyRef(r, ref m) => (m.mutbl, r),
 769                     _ => span_bug!(expr.span,
 770                                    "bad overloaded deref type {:?}",
 771                                    method_ty)
 772                 };
 773                 let bk = ty::BorrowKind::from_mutbl(m);
 774                 self.delegate.borrow(expr.id, expr.span, cmt,
 775                                      r, bk, AutoRef);
 776             }
 777         }
 778     }
 779
 780     /// Walks the autoref `opt_autoref` applied to the autoderef'd
 781     /// `expr`. `cmt_derefd` is the mem-categorized form of `expr`
 782     /// after all relevant autoderefs have occurred. Because AutoRefs
 783     /// can be recursive, this function is recursive: it first walks
 784     /// deeply all the way down the autoref chain, and then processes
 785     /// the autorefs on the way out. At each point, it returns the
 786     /// `cmt` for the rvalue that will be produced by introduced an
 787     /// autoref.
 788     fn walk_autoref(&mut self,
 789                     expr: &hir::Expr,
 790                     cmt_base: mc::cmt<'tcx>,
 791                     opt_autoref: Option<adjustment::AutoBorrow<'tcx>>)
 792                     -> mc::cmt<'tcx>
 793     {
 794         debug!("walk_autoref(expr.id={} cmt_derefd={:?} opt_autoref={:?})",
 795                expr.id,
 796                cmt_base,
 797                opt_autoref);
 798
 799         let cmt_base_ty = cmt_base.ty;
 800
 801         let autoref = match opt_autoref {
 802             Some(ref autoref) => autoref,
 803             None => {
 804                 // No AutoRef.
 805                 return cmt_base;
 806             }
 807         };
 808
 809         match *autoref {
 810             adjustment::AutoBorrow::Ref(r, m) => {
 811                 self.delegate.borrow(expr.id,
 812                                      expr.span,
 813                                      cmt_base,
 814                                      r,
 815                                      ty::BorrowKind::from_mutbl(m),
 816                                      AutoRef);
 817             }
 818
 819             adjustment::AutoBorrow::RawPtr(m) => {
 820                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 821                        expr.id,
 822                        cmt_base);
 823
 824                 // Converting from a &T to *T (or &mut T to *mut T) is
 825                 // treated as borrowing it for the enclosing temporary
 826                 // scope.
 827                 let r = self.tcx().node_scope_region(expr.id);
 828
 829                 self.delegate.borrow(expr.id,
 830                                      expr.span,
 831                                      cmt_base,
 832                                      r,
 833                                      ty::BorrowKind::from_mutbl(m),
 834                                      AutoUnsafe);
 835             }
 836         }
 837
 838         // Construct the categorization for the result of the autoref.
 839         // This is always an rvalue, since we are producing a new
 840         // (temporary) indirection.
 841
 842         let adj_ty = cmt_base_ty.adjust_for_autoref(self.tcx(), opt_autoref);
 843
 844         self.mc.cat_rvalue_node(expr.id, expr.span, adj_ty)
 845     }
 846
 847
 848     // When this returns true, it means that the expression *is* a
 849     // method-call (i.e. via the operator-overload).  This true result
 850     // also implies that walk_overloaded_operator already took care of
 851     // recursively processing the input arguments, and thus the caller
 852     // should not do so.
 853     fn walk_overloaded_operator(&mut self,
 854                                 expr: &hir::Expr,
 855                                 receiver: &hir::Expr,
 856                                 rhs: Vec<&hir::Expr>,
 857                                 pass_args: PassArgs)
 858                                 -> bool
 859     {
 860         if !self.mc.infcx.is_method_call(expr.id) {
 861             return false;
 862         }
 863
 864         match pass_args {
 865             PassArgs::ByValue => {
 866                 self.consume_expr(receiver);
 867                 for &arg in &rhs {
 868                     self.consume_expr(arg);
 869                 }
 870
 871                 return true;
 872             },
 873             PassArgs::ByRef => {},
 874         }
 875
 876         self.walk_expr(receiver);
 877
 878         // Arguments (but not receivers) to overloaded operator
 879         // methods are implicitly autoref'd which sadly does not use
 880         // adjustments, so we must hardcode the borrow here.
 881
 882         let r = self.tcx().node_scope_region(expr.id);
 883         let bk = ty::ImmBorrow;
 884
 885         for &arg in &rhs {
 886             self.borrow_expr(arg, r, bk, OverloadedOperator);
 887         }
 888         return true;
 889     }
 890
 891     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 892         let mut mode = Unknown;
 893         for pat in &arm.pats {
 894             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 895         }
 896         mode
 897     }
 898
 899     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 900         for pat in &arm.pats {
 901             self.walk_pat(discr_cmt.clone(), &pat, mode);
 902         }
 903
 904         if let Some(ref guard) = arm.guard {
 905             self.consume_expr(&guard);
 906         }
 907
 908         self.consume_expr(&arm.body);
 909     }
 910
 911     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 912     /// arg or let binding.  *Not* a match arm or nested pat.)
 913     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 914         let mut mode = Unknown;
 915         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 916         let mode = mode.match_mode();
 917         self.walk_pat(cmt_discr, pat, mode);
 918     }
 919
 920     /// Identifies any bindings within `pat` and accumulates within
 921     /// `mode` whether the overall pattern/match structure is a move,
 922     /// copy, or borrow.
 923     fn determine_pat_move_mode(&mut self,
 924                                cmt_discr: mc::cmt<'tcx>,
 925                                pat: &hir::Pat,
 926                                mode: &mut TrackMatchMode) {
 927         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 928                pat);
 929         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 930             match pat.node {
 931                 PatKind::Binding(hir::BindByRef(..), ..) =>
 932                     mode.lub(BorrowingMatch),
 933                 PatKind::Binding(hir::BindByValue(..), ..) => {
 934                     match copy_or_move(self.mc.infcx, &cmt_pat, PatBindingMove) {
 935                         Copy => mode.lub(CopyingMatch),
 936                         Move(..) => mode.lub(MovingMatch),
 937                     }
 938                 }
 939                 _ => {}
 940             }
 941         }));
 942     }
 943
 944     /// The core driver for walking a pattern; `match_mode` must be
 945     /// established up front, e.g. via `determine_pat_move_mode` (see
 946     /// also `walk_irrefutable_pat` for patterns that stand alone).
 947     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 948         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 949
 950         let tcx = &self.tcx();
 951         let mc = &self.mc;
 952         let infcx = self.mc.infcx;
 953         let delegate = &mut self.delegate;
 954         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 955             if let PatKind::Binding(bmode, def_id, ..) = pat.node {
 956                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 957
 958                 // pat_ty: the type of the binding being produced.
 959                 let pat_ty = return_if_err!(infcx.node_ty(pat.id));
 960
 961                 // Each match binding is effectively an assignment to the
 962                 // binding being produced.
 963                 let def = Def::Local(def_id);
 964                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 965                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 966                 }
 967
 968                 // It is also a borrow or copy/move of the value being matched.
 969                 match bmode {
 970                     hir::BindByRef(m) => {
 971                         if let ty::TyRef(r, _) = pat_ty.sty {
 972                             let bk = ty::BorrowKind::from_mutbl(m);
 973                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 974                         }
 975                     }
 976                     hir::BindByValue(..) => {
 977                         let mode = copy_or_move(infcx, &cmt_pat, PatBindingMove);
 978                         debug!("walk_pat binding consuming pat");
 979                         delegate.consume_pat(pat, cmt_pat, mode);
 980                     }
 981                 }
 982             }
 983         }));
 984
 985         // Do a second pass over the pattern, calling `matched_pat` on
 986         // the interior nodes (enum variants and structs), as opposed
 987         // to the above loop's visit of than the bindings that form
 988         // the leaves of the pattern tree structure.
 989         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
 990             let qpath = match pat.node {
 991                 PatKind::Path(ref qpath) |
 992                 PatKind::TupleStruct(ref qpath, ..) |
 993                 PatKind::Struct(ref qpath, ..) => qpath,
 994                 _ => return
 995             };
 996             let def = infcx.tables.borrow().qpath_def(qpath, pat.id);
 997             match def {
 998                 Def::Variant(variant_did) |
 999                 Def::VariantCtor(variant_did, ..) => {
1000                     let enum_did = tcx.parent_def_id(variant_did).unwrap();
1001                     let downcast_cmt = if tcx.adt_def(enum_did).is_univariant() {
1002                         cmt_pat
1003                     } else {
1004                         let cmt_pat_ty = cmt_pat.ty;
1005                         mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1006                     };
1007
1008                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
1009                     delegate.matched_pat(pat, downcast_cmt, match_mode);
1010                 }
1011                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
1012                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
1013                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
1014                     delegate.matched_pat(pat, cmt_pat, match_mode);
1015                 }
1016                 _ => {}
1017             }
1018         }));
1019     }
1020
1021     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
1022         debug!("walk_captures({:?})", closure_expr);
1023
1024         self.tcx().with_freevars(closure_expr.id, |freevars| {
1025             for freevar in freevars {
1026                 let def_id = freevar.def.def_id();
1027                 let id_var = self.tcx().hir.as_local_node_id(def_id).unwrap();
1028                 let upvar_id = ty::UpvarId { var_id: id_var,
1029                                              closure_expr_id: closure_expr.id };
1030                 let upvar_capture = self.mc.infcx.upvar_capture(upvar_id).unwrap();
1031                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1032                                                                    fn_decl_span,
1033                                                                    freevar.def));
1034                 match upvar_capture {
1035                     ty::UpvarCapture::ByValue => {
1036                         let mode = copy_or_move(self.mc.infcx, &cmt_var, CaptureMove);
1037                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1038                     }
1039                     ty::UpvarCapture::ByRef(upvar_borrow) => {
1040                         self.delegate.borrow(closure_expr.id,
1041                                              fn_decl_span,
1042                                              cmt_var,
1043                                              upvar_borrow.region,
1044                                              upvar_borrow.kind,
1045                                              ClosureCapture(freevar.span));
1046                     }
1047                 }
1048             }
1049         });
1050     }
1051
1052     fn cat_captured_var(&mut self,
1053                         closure_id: ast::NodeId,
1054                         closure_span: Span,
1055                         upvar_def: Def)
1056                         -> mc::McResult<mc::cmt<'tcx>> {
1057         // Create the cmt for the variable being borrowed, from the
1058         // caller's perspective
1059         let var_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
1060         let var_ty = self.mc.infcx.node_ty(var_id)?;
1061         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1062     }
1063 }
1064
1065 fn copy_or_move<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
1066                                 cmt: &mc::cmt<'tcx>,
1067                                 move_reason: MoveReason)
1068                                 -> ConsumeMode
1069 {
1070     if infcx.type_moves_by_default(cmt.ty, cmt.span) {
1071         Move(move_reason)
1072     } else {
1073         Copy
1074     }
1075 }