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