src/librustc/middle/expr_use_visitor.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A different sort of visitor for walking fn bodies.  Unlike the
  12 //! normal visitor, which just walks the entire body in one shot, the
  13 //! `ExprUseVisitor` determines how expressions are being used.
  14
  15 pub use self::MutateMode::*;
  16 pub use self::LoanCause::*;
  17 pub use self::ConsumeMode::*;
  18 pub use self::MoveReason::*;
  19 pub use self::MatchMode::*;
  20 use self::TrackMatchMode::*;
  21 use self::OverloadedCallType::*;
  22
  23 use middle::{def, pat_util};
  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 //
 246 // FIXME(stage0): the :'t here is probably only important for stage0
 247 pub struct ExprUseVisitor<'d, 't, 'a: 't, 'tcx:'a+'d+'t> {
 248     typer: &'t infer::InferCtxt<'a, 'tcx>,
 249     mc: mc::MemCategorizationContext<'t, 'a, 'tcx>,
 250     delegate: &'d mut Delegate<'tcx>,
 251 }
 252
 253 // If the TYPER results in an error, it's because the type check
 254 // failed (or will fail, when the error is uncovered and reported
 255 // during writeback). In this case, we just ignore this part of the
 256 // code.
 257 //
 258 // Note that this macro appears similar to try!(), but, unlike try!(),
 259 // it does not propagate the error.
 260 macro_rules! return_if_err {
 261     ($inp: expr) => (
 262         match $inp {
 263             Ok(v) => v,
 264             Err(()) => {
 265                 debug!("mc reported err");
 266                 return
 267             }
 268         }
 269     )
 270 }
 271
 272 /// Whether the elements of an overloaded operation are passed by value or by reference
 273 enum PassArgs {
 274     ByValue,
 275     ByRef,
 276 }
 277
 278 impl<'d,'t,'a,'tcx> ExprUseVisitor<'d,'t,'a,'tcx> {
 279     pub fn new(delegate: &'d mut Delegate<'tcx>,
 280                typer: &'t infer::InferCtxt<'a, 'tcx>)
 281                -> ExprUseVisitor<'d,'t,'a,'tcx>
 282     {
 283         let result = ExprUseVisitor {
 284             typer: typer,
 285             mc: mc::MemCategorizationContext::new(typer),
 286             delegate: delegate,
 287         };
 288
 289         result
 290     }
 291
 292     pub fn walk_fn(&mut self,
 293                    decl: &hir::FnDecl,
 294                    body: &hir::Block) {
 295         self.walk_arg_patterns(decl, body);
 296         self.walk_block(body);
 297     }
 298
 299     fn walk_arg_patterns(&mut self,
 300                          decl: &hir::FnDecl,
 301                          body: &hir::Block) {
 302         for arg in &decl.inputs {
 303             let arg_ty = return_if_err!(self.typer.node_ty(arg.pat.id));
 304
 305             let fn_body_scope = self.tcx().region_maps.node_extent(body.id);
 306             let arg_cmt = self.mc.cat_rvalue(
 307                 arg.id,
 308                 arg.pat.span,
 309                 ty::ReScope(fn_body_scope), // Args live only as long as the fn body.
 310                 arg_ty);
 311
 312             self.walk_irrefutable_pat(arg_cmt, &*arg.pat);
 313         }
 314     }
 315
 316     fn tcx(&self) -> &'t ty::ctxt<'tcx> {
 317         self.typer.tcx
 318     }
 319
 320     fn delegate_consume(&mut self,
 321                         consume_id: ast::NodeId,
 322                         consume_span: Span,
 323                         cmt: mc::cmt<'tcx>) {
 324         debug!("delegate_consume(consume_id={}, cmt={:?})",
 325                consume_id, cmt);
 326
 327         let mode = copy_or_move(self.typer, &cmt, DirectRefMove);
 328         self.delegate.consume(consume_id, consume_span, cmt, mode);
 329     }
 330
 331     fn consume_exprs(&mut self, exprs: &Vec<P<hir::Expr>>) {
 332         for expr in exprs {
 333             self.consume_expr(&**expr);
 334         }
 335     }
 336
 337     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 338         debug!("consume_expr(expr={:?})", expr);
 339
 340         let cmt = return_if_err!(self.mc.cat_expr(expr));
 341         self.delegate_consume(expr.id, expr.span, cmt);
 342         self.walk_expr(expr);
 343     }
 344
 345     fn mutate_expr(&mut self,
 346                    assignment_expr: &hir::Expr,
 347                    expr: &hir::Expr,
 348                    mode: MutateMode) {
 349         let cmt = return_if_err!(self.mc.cat_expr(expr));
 350         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 351         self.walk_expr(expr);
 352     }
 353
 354     fn borrow_expr(&mut self,
 355                    expr: &hir::Expr,
 356                    r: ty::Region,
 357                    bk: ty::BorrowKind,
 358                    cause: LoanCause) {
 359         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 360                expr, r, bk);
 361
 362         let cmt = return_if_err!(self.mc.cat_expr(expr));
 363         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 364
 365         // Note: Unlike consume, we can ignore ExprParen. cat_expr
 366         // already skips over them, and walk will uncover any
 367         // attachments or whatever.
 368         self.walk_expr(expr)
 369     }
 370
 371     fn select_from_expr(&mut self, expr: &hir::Expr) {
 372         self.walk_expr(expr)
 373     }
 374
 375     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 376         debug!("walk_expr(expr={:?})", expr);
 377
 378         self.walk_adjustment(expr);
 379
 380         match expr.node {
 381             hir::ExprParen(ref subexpr) => {
 382                 self.walk_expr(&**subexpr)
 383             }
 384
 385             hir::ExprPath(..) => { }
 386
 387             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 388                 if !self.walk_overloaded_operator(expr, &**base, Vec::new(), PassArgs::ByRef) {
 389                     self.select_from_expr(&**base);
 390                 }
 391             }
 392
 393             hir::ExprField(ref base, _) => {         // base.f
 394                 self.select_from_expr(&**base);
 395             }
 396
 397             hir::ExprTupField(ref base, _) => {         // base.<n>
 398                 self.select_from_expr(&**base);
 399             }
 400
 401             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 402                 if !self.walk_overloaded_operator(expr,
 403                                                   &**lhs,
 404                                                   vec![&**rhs],
 405                                                   PassArgs::ByValue) {
 406                     self.select_from_expr(&**lhs);
 407                     self.consume_expr(&**rhs);
 408                 }
 409             }
 410
 411             hir::ExprRange(ref start, ref end) => {
 412                 start.as_ref().map(|e| self.consume_expr(&**e));
 413                 end.as_ref().map(|e| self.consume_expr(&**e));
 414             }
 415
 416             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 417                 self.walk_callee(expr, &**callee);
 418                 self.consume_exprs(args);
 419             }
 420
 421             hir::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 422                 self.consume_exprs(args);
 423             }
 424
 425             hir::ExprStruct(_, ref fields, ref opt_with) => {
 426                 self.walk_struct_expr(expr, fields, opt_with);
 427             }
 428
 429             hir::ExprTup(ref exprs) => {
 430                 self.consume_exprs(exprs);
 431             }
 432
 433             hir::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
 434                 self.consume_expr(&**cond_expr);
 435                 self.walk_block(&**then_blk);
 436                 if let Some(ref else_expr) = *opt_else_expr {
 437                     self.consume_expr(&**else_expr);
 438                 }
 439             }
 440
 441             hir::ExprMatch(ref discr, ref arms, _) => {
 442                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
 443                 self.borrow_expr(&**discr, ty::ReEmpty, ty::ImmBorrow, MatchDiscriminant);
 444
 445                 // treatment of the discriminant is handled while walking the arms.
 446                 for arm in arms {
 447                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 448                     let mode = mode.match_mode();
 449                     self.walk_arm(discr_cmt.clone(), arm, mode);
 450                 }
 451             }
 452
 453             hir::ExprVec(ref exprs) => {
 454                 self.consume_exprs(exprs);
 455             }
 456
 457             hir::ExprAddrOf(m, ref base) => {   // &base
 458                 // make sure that the thing we are pointing out stays valid
 459                 // for the lifetime `scope_r` of the resulting ptr:
 460                 let expr_ty = return_if_err!(self.typer.node_ty(expr.id));
 461                 if let ty::TyRef(&r, _) = expr_ty.sty {
 462                     let bk = ty::BorrowKind::from_mutbl(m);
 463                     self.borrow_expr(&**base, r, bk, AddrOf);
 464                 }
 465             }
 466
 467             hir::ExprInlineAsm(ref ia) => {
 468                 for &(_, ref input) in &ia.inputs {
 469                     self.consume_expr(&**input);
 470                 }
 471
 472                 for &(_, ref output, is_rw) in &ia.outputs {
 473                     self.mutate_expr(expr, &**output,
 474                                            if is_rw { WriteAndRead } else { JustWrite });
 475                 }
 476             }
 477
 478             hir::ExprBreak(..) |
 479             hir::ExprAgain(..) |
 480             hir::ExprLit(..) => {}
 481
 482             hir::ExprLoop(ref blk, _) => {
 483                 self.walk_block(&**blk);
 484             }
 485
 486             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 487                 self.consume_expr(&**cond_expr);
 488                 self.walk_block(&**blk);
 489             }
 490
 491             hir::ExprUnary(op, ref lhs) => {
 492                 let pass_args = if ::rustc_front::util::is_by_value_unop(op) {
 493                     PassArgs::ByValue
 494                 } else {
 495                     PassArgs::ByRef
 496                 };
 497
 498                 if !self.walk_overloaded_operator(expr, &**lhs, Vec::new(), pass_args) {
 499                     self.consume_expr(&**lhs);
 500                 }
 501             }
 502
 503             hir::ExprBinary(op, ref lhs, ref rhs) => {
 504                 let pass_args = if ::rustc_front::util::is_by_value_binop(op.node) {
 505                     PassArgs::ByValue
 506                 } else {
 507                     PassArgs::ByRef
 508                 };
 509
 510                 if !self.walk_overloaded_operator(expr, &**lhs, vec![&**rhs], pass_args) {
 511                     self.consume_expr(&**lhs);
 512                     self.consume_expr(&**rhs);
 513                 }
 514             }
 515
 516             hir::ExprBlock(ref blk) => {
 517                 self.walk_block(&**blk);
 518             }
 519
 520             hir::ExprRet(ref opt_expr) => {
 521                 if let Some(ref expr) = *opt_expr {
 522                     self.consume_expr(&**expr);
 523                 }
 524             }
 525
 526             hir::ExprAssign(ref lhs, ref rhs) => {
 527                 self.mutate_expr(expr, &**lhs, JustWrite);
 528                 self.consume_expr(&**rhs);
 529             }
 530
 531             hir::ExprCast(ref base, _) => {
 532                 self.consume_expr(&**base);
 533             }
 534
 535             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 536                 // This will have to change if/when we support
 537                 // overloaded operators for `+=` and so forth.
 538                 self.mutate_expr(expr, &**lhs, WriteAndRead);
 539                 self.consume_expr(&**rhs);
 540             }
 541
 542             hir::ExprRepeat(ref base, ref count) => {
 543                 self.consume_expr(&**base);
 544                 self.consume_expr(&**count);
 545             }
 546
 547             hir::ExprClosure(..) => {
 548                 self.walk_captures(expr)
 549             }
 550
 551             hir::ExprBox(ref place, ref base) => {
 552                 match *place {
 553                     Some(ref place) => self.consume_expr(&**place),
 554                     None => {}
 555                 }
 556                 self.consume_expr(&**base);
 557                 if place.is_some() {
 558                     self.tcx().sess.span_bug(
 559                         expr.span,
 560                         "box with explicit place remains after expansion");
 561                 }
 562             }
 563         }
 564     }
 565
 566     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 567         let callee_ty = return_if_err!(self.typer.expr_ty_adjusted(callee));
 568         debug!("walk_callee: callee={:?} callee_ty={:?}",
 569                callee, callee_ty);
 570         let call_scope = self.tcx().region_maps.node_extent(call.id);
 571         match callee_ty.sty {
 572             ty::TyBareFn(..) => {
 573                 self.consume_expr(callee);
 574             }
 575             ty::TyError => { }
 576             _ => {
 577                 let overloaded_call_type =
 578                     match self.typer.node_method_id(ty::MethodCall::expr(call.id)) {
 579                         Some(method_id) => {
 580                             OverloadedCallType::from_method_id(self.tcx(), method_id)
 581                         }
 582                         None => {
 583                             self.tcx().sess.span_bug(
 584                                 callee.span,
 585                                 &format!("unexpected callee type {}", callee_ty))
 586                         }
 587                     };
 588                 match overloaded_call_type {
 589                     FnMutOverloadedCall => {
 590                         self.borrow_expr(callee,
 591                                          ty::ReScope(call_scope),
 592                                          ty::MutBorrow,
 593                                          ClosureInvocation);
 594                     }
 595                     FnOverloadedCall => {
 596                         self.borrow_expr(callee,
 597                                          ty::ReScope(call_scope),
 598                                          ty::ImmBorrow,
 599                                          ClosureInvocation);
 600                     }
 601                     FnOnceOverloadedCall => self.consume_expr(callee),
 602                 }
 603             }
 604         }
 605     }
 606
 607     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 608         match stmt.node {
 609             hir::StmtDecl(ref decl, _) => {
 610                 match decl.node {
 611                     hir::DeclLocal(ref local) => {
 612                         self.walk_local(&**local);
 613                     }
 614
 615                     hir::DeclItem(_) => {
 616                         // we don't visit nested items in this visitor,
 617                         // only the fn body we were given.
 618                     }
 619                 }
 620             }
 621
 622             hir::StmtExpr(ref expr, _) |
 623             hir::StmtSemi(ref expr, _) => {
 624                 self.consume_expr(&**expr);
 625             }
 626         }
 627     }
 628
 629     fn walk_local(&mut self, local: &hir::Local) {
 630         match local.init {
 631             None => {
 632                 let delegate = &mut self.delegate;
 633                 pat_util::pat_bindings(&self.typer.tcx.def_map, &*local.pat,
 634                                        |_, id, span, _| {
 635                     delegate.decl_without_init(id, span);
 636                 })
 637             }
 638
 639             Some(ref expr) => {
 640                 // Variable declarations with
 641                 // initializers are considered
 642                 // "assigns", which is handled by
 643                 // `walk_pat`:
 644                 self.walk_expr(&**expr);
 645                 let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
 646                 self.walk_irrefutable_pat(init_cmt, &*local.pat);
 647             }
 648         }
 649     }
 650
 651     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 652     /// depending on its type.
 653     fn walk_block(&mut self, blk: &hir::Block) {
 654         debug!("walk_block(blk.id={})", blk.id);
 655
 656         for stmt in &blk.stmts {
 657             self.walk_stmt(&**stmt);
 658         }
 659
 660         if let Some(ref tail_expr) = blk.expr {
 661             self.consume_expr(&**tail_expr);
 662         }
 663     }
 664
 665     fn walk_struct_expr(&mut self,
 666                         _expr: &hir::Expr,
 667                         fields: &Vec<hir::Field>,
 668                         opt_with: &Option<P<hir::Expr>>) {
 669         // Consume the expressions supplying values for each field.
 670         for field in fields {
 671             self.consume_expr(&*field.expr);
 672         }
 673
 674         let with_expr = match *opt_with {
 675             Some(ref w) => &**w,
 676             None => { return; }
 677         };
 678
 679         let with_cmt = return_if_err!(self.mc.cat_expr(&*with_expr));
 680
 681         // Select just those fields of the `with`
 682         // expression that will actually be used
 683         if let ty::TyStruct(def, substs) = with_cmt.ty.sty {
 684             // Consume those fields of the with expression that are needed.
 685             for with_field in &def.struct_variant().fields {
 686                 if !contains_field_named(with_field, fields) {
 687                     let cmt_field = self.mc.cat_field(
 688                         &*with_expr,
 689                         with_cmt.clone(),
 690                         with_field.name,
 691                         with_field.ty(self.tcx(), substs)
 692                     );
 693                     self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 694                 }
 695             }
 696         } else {
 697             // the base expression should always evaluate to a
 698             // struct; however, when EUV is run during typeck, it
 699             // may not. This will generate an error earlier in typeck,
 700             // so we can just ignore it.
 701             if !self.tcx().sess.has_errors() {
 702                 self.tcx().sess.span_bug(
 703                     with_expr.span,
 704                     "with expression doesn't evaluate to a struct");
 705             }
 706         };
 707
 708         // walk the with expression so that complex expressions
 709         // are properly handled.
 710         self.walk_expr(with_expr);
 711
 712         fn contains_field_named(field: ty::FieldDef,
 713                                 fields: &Vec<hir::Field>)
 714                                 -> bool
 715         {
 716             fields.iter().any(
 717                 |f| f.ident.node.name == field.name)
 718         }
 719     }
 720
 721     // Invoke the appropriate delegate calls for anything that gets
 722     // consumed or borrowed as part of the automatic adjustment
 723     // process.
 724     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 725         let typer = self.typer;
 726         //NOTE(@jroesch): mixed RefCell borrow causes crash
 727         let adj = typer.adjustments().get(&expr.id).map(|x| x.clone());
 728         if let Some(adjustment) = adj {
 729             match adjustment {
 730                 adjustment::AdjustReifyFnPointer |
 731                 adjustment::AdjustUnsafeFnPointer => {
 732                     // Creating a closure/fn-pointer or unsizing consumes
 733                     // the input and stores it into the resulting rvalue.
 734                     debug!("walk_adjustment(AdjustReifyFnPointer|AdjustUnsafeFnPointer)");
 735                     let cmt_unadjusted =
 736                         return_if_err!(self.mc.cat_expr_unadjusted(expr));
 737                     self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 738                 }
 739                 adjustment::AdjustDerefRef(ref adj) => {
 740                     self.walk_autoderefref(expr, adj);
 741                 }
 742             }
 743         }
 744     }
 745
 746     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 747     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 748     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 749     fn walk_autoderefs(&mut self,
 750                        expr: &hir::Expr,
 751                        autoderefs: usize) {
 752         debug!("walk_autoderefs expr={:?} autoderefs={}", expr, autoderefs);
 753
 754         for i in 0..autoderefs {
 755             let deref_id = ty::MethodCall::autoderef(expr.id, i as u32);
 756             match self.typer.node_method_ty(deref_id) {
 757                 None => {}
 758                 Some(method_ty) => {
 759                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 760
 761                     // the method call infrastructure should have
 762                     // replaced all late-bound regions with variables:
 763                     let self_ty = method_ty.fn_sig().input(0);
 764                     let self_ty = self.tcx().no_late_bound_regions(&self_ty).unwrap();
 765
 766                     let (m, r) = match self_ty.sty {
 767                         ty::TyRef(r, ref m) => (m.mutbl, r),
 768                         _ => self.tcx().sess.span_bug(expr.span,
 769                                 &format!("bad overloaded deref type {:?}",
 770                                     method_ty))
 771                     };
 772                     let bk = ty::BorrowKind::from_mutbl(m);
 773                     self.delegate.borrow(expr.id, expr.span, cmt,
 774                                          *r, bk, AutoRef);
 775                 }
 776             }
 777         }
 778     }
 779
 780     fn walk_autoderefref(&mut self,
 781                          expr: &hir::Expr,
 782                          adj: &adjustment::AutoDerefRef<'tcx>) {
 783         debug!("walk_autoderefref expr={:?} adj={:?}",
 784                expr,
 785                adj);
 786
 787         self.walk_autoderefs(expr, adj.autoderefs);
 788
 789         let cmt_derefd =
 790             return_if_err!(self.mc.cat_expr_autoderefd(expr, adj.autoderefs));
 791
 792         let cmt_refd =
 793             self.walk_autoref(expr, cmt_derefd, adj.autoref);
 794
 795         if adj.unsize.is_some() {
 796             // Unsizing consumes the thin pointer and produces a fat one.
 797             self.delegate_consume(expr.id, expr.span, cmt_refd);
 798         }
 799     }
 800
 801
 802     /// Walks the autoref `opt_autoref` applied to the autoderef'd
 803     /// `expr`. `cmt_derefd` is the mem-categorized form of `expr`
 804     /// after all relevant autoderefs have occurred. Because AutoRefs
 805     /// can be recursive, this function is recursive: it first walks
 806     /// deeply all the way down the autoref chain, and then processes
 807     /// the autorefs on the way out. At each point, it returns the
 808     /// `cmt` for the rvalue that will be produced by introduced an
 809     /// autoref.
 810     fn walk_autoref(&mut self,
 811                     expr: &hir::Expr,
 812                     cmt_base: mc::cmt<'tcx>,
 813                     opt_autoref: Option<adjustment::AutoRef<'tcx>>)
 814                     -> mc::cmt<'tcx>
 815     {
 816         debug!("walk_autoref(expr.id={} cmt_derefd={:?} opt_autoref={:?})",
 817                expr.id,
 818                cmt_base,
 819                opt_autoref);
 820
 821         let cmt_base_ty = cmt_base.ty;
 822
 823         let autoref = match opt_autoref {
 824             Some(ref autoref) => autoref,
 825             None => {
 826                 // No AutoRef.
 827                 return cmt_base;
 828             }
 829         };
 830
 831         match *autoref {
 832             adjustment::AutoPtr(r, m) => {
 833                 self.delegate.borrow(expr.id,
 834                                      expr.span,
 835                                      cmt_base,
 836                                      *r,
 837                                      ty::BorrowKind::from_mutbl(m),
 838                                      AutoRef);
 839             }
 840
 841             adjustment::AutoUnsafe(m) => {
 842                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 843                        expr.id,
 844                        cmt_base);
 845
 846                 // Converting from a &T to *T (or &mut T to *mut T) is
 847                 // treated as borrowing it for the enclosing temporary
 848                 // scope.
 849                 let r = ty::ReScope(self.tcx().region_maps.node_extent(expr.id));
 850
 851                 self.delegate.borrow(expr.id,
 852                                      expr.span,
 853                                      cmt_base,
 854                                      r,
 855                                      ty::BorrowKind::from_mutbl(m),
 856                                      AutoUnsafe);
 857             }
 858         }
 859
 860         // Construct the categorization for the result of the autoref.
 861         // This is always an rvalue, since we are producing a new
 862         // (temporary) indirection.
 863
 864         let adj_ty = cmt_base_ty.adjust_for_autoref(self.tcx(), opt_autoref);
 865
 866         self.mc.cat_rvalue_node(expr.id, expr.span, adj_ty)
 867     }
 868
 869
 870     // When this returns true, it means that the expression *is* a
 871     // method-call (i.e. via the operator-overload).  This true result
 872     // also implies that walk_overloaded_operator already took care of
 873     // recursively processing the input arguments, and thus the caller
 874     // should not do so.
 875     fn walk_overloaded_operator(&mut self,
 876                                 expr: &hir::Expr,
 877                                 receiver: &hir::Expr,
 878                                 rhs: Vec<&hir::Expr>,
 879                                 pass_args: PassArgs)
 880                                 -> bool
 881     {
 882         if !self.typer.is_method_call(expr.id) {
 883             return false;
 884         }
 885
 886         match pass_args {
 887             PassArgs::ByValue => {
 888                 self.consume_expr(receiver);
 889                 for &arg in &rhs {
 890                     self.consume_expr(arg);
 891                 }
 892
 893                 return true;
 894             },
 895             PassArgs::ByRef => {},
 896         }
 897
 898         self.walk_expr(receiver);
 899
 900         // Arguments (but not receivers) to overloaded operator
 901         // methods are implicitly autoref'd which sadly does not use
 902         // adjustments, so we must hardcode the borrow here.
 903
 904         let r = ty::ReScope(self.tcx().region_maps.node_extent(expr.id));
 905         let bk = ty::ImmBorrow;
 906
 907         for &arg in &rhs {
 908             self.borrow_expr(arg, r, bk, OverloadedOperator);
 909         }
 910         return true;
 911     }
 912
 913     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 914         let mut mode = Unknown;
 915         for pat in &arm.pats {
 916             self.determine_pat_move_mode(discr_cmt.clone(), &**pat, &mut mode);
 917         }
 918         mode
 919     }
 920
 921     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 922         for pat in &arm.pats {
 923             self.walk_pat(discr_cmt.clone(), &**pat, mode);
 924         }
 925
 926         if let Some(ref guard) = arm.guard {
 927             self.consume_expr(&**guard);
 928         }
 929
 930         self.consume_expr(&*arm.body);
 931     }
 932
 933     /// Walks an pat that occurs in isolation (i.e. top-level of fn
 934     /// arg or let binding.  *Not* a match arm or nested pat.)
 935     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 936         let mut mode = Unknown;
 937         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 938         let mode = mode.match_mode();
 939         self.walk_pat(cmt_discr, pat, mode);
 940     }
 941
 942     /// Identifies any bindings within `pat` and accumulates within
 943     /// `mode` whether the overall pattern/match structure is a move,
 944     /// copy, or borrow.
 945     fn determine_pat_move_mode(&mut self,
 946                                cmt_discr: mc::cmt<'tcx>,
 947                                pat: &hir::Pat,
 948                                mode: &mut TrackMatchMode) {
 949         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 950                pat);
 951         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 952             let tcx = self.tcx();
 953             let def_map = &self.tcx().def_map;
 954             if pat_util::pat_is_binding(def_map, pat) {
 955                 match pat.node {
 956                     hir::PatIdent(hir::BindByRef(_), _, _) =>
 957                         mode.lub(BorrowingMatch),
 958                     hir::PatIdent(hir::BindByValue(_), _, _) => {
 959                         match copy_or_move(self.typer, &cmt_pat, PatBindingMove) {
 960                             Copy => mode.lub(CopyingMatch),
 961                             Move(_) => mode.lub(MovingMatch),
 962                         }
 963                     }
 964                     _ => {
 965                         tcx.sess.span_bug(
 966                             pat.span,
 967                             "binding pattern not an identifier");
 968                     }
 969                 }
 970             }
 971         }));
 972     }
 973
 974     /// The core driver for walking a pattern; `match_mode` must be
 975     /// established up front, e.g. via `determine_pat_move_mode` (see
 976     /// also `walk_irrefutable_pat` for patterns that stand alone).
 977     fn walk_pat(&mut self,
 978                 cmt_discr: mc::cmt<'tcx>,
 979                 pat: &hir::Pat,
 980                 match_mode: MatchMode) {
 981         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr,
 982                pat);
 983
 984         let mc = &self.mc;
 985         let typer = self.typer;
 986         let def_map = &self.tcx().def_map;
 987         let delegate = &mut self.delegate;
 988         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 989             if pat_util::pat_is_binding(def_map, pat) {
 990                 let tcx = typer.tcx;
 991
 992                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}",
 993                        cmt_pat,
 994                        pat,
 995                        match_mode);
 996
 997                 // pat_ty: the type of the binding being produced.
 998                 let pat_ty = return_if_err!(typer.node_ty(pat.id));
 999
1000                 // Each match binding is effectively an assignment to the
1001                 // binding being produced.
1002                 let def = def_map.borrow().get(&pat.id).unwrap().full_def();
1003                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
1004                     Ok(binding_cmt) => {
1005                         delegate.mutate(pat.id, pat.span, binding_cmt, Init);
1006                     }
1007                     Err(_) => { }
1008                 }
1009
1010                 // It is also a borrow or copy/move of the value being matched.
1011                 match pat.node {
1012                     hir::PatIdent(hir::BindByRef(m), _, _) => {
1013                         if let ty::TyRef(&r, _) = pat_ty.sty {
1014                             let bk = ty::BorrowKind::from_mutbl(m);
1015                             delegate.borrow(pat.id, pat.span, cmt_pat,
1016                                             r, bk, RefBinding);
1017                         }
1018                     }
1019                     hir::PatIdent(hir::BindByValue(_), _, _) => {
1020                         let mode = copy_or_move(typer, &cmt_pat, PatBindingMove);
1021                         debug!("walk_pat binding consuming pat");
1022                         delegate.consume_pat(pat, cmt_pat, mode);
1023                     }
1024                     _ => {
1025                         tcx.sess.span_bug(
1026                             pat.span,
1027                             "binding pattern not an identifier");
1028                     }
1029                 }
1030             } else {
1031                 match pat.node {
1032                     hir::PatVec(_, Some(ref slice_pat), _) => {
1033                         // The `slice_pat` here creates a slice into
1034                         // the original vector.  This is effectively a
1035                         // borrow of the elements of the vector being
1036                         // matched.
1037
1038                         let (slice_cmt, slice_mutbl, slice_r) =
1039                             return_if_err!(mc.cat_slice_pattern(cmt_pat, &**slice_pat));
1040
1041                         // Note: We declare here that the borrow
1042                         // occurs upon entering the `[...]`
1043                         // pattern. This implies that something like
1044                         // `[a; b]` where `a` is a move is illegal,
1045                         // because the borrow is already in effect.
1046                         // In fact such a move would be safe-ish, but
1047                         // it effectively *requires* that we use the
1048                         // nulling out semantics to indicate when a
1049                         // value has been moved, which we are trying
1050                         // to move away from.  Otherwise, how can we
1051                         // indicate that the first element in the
1052                         // vector has been moved?  Eventually, we
1053                         // could perhaps modify this rule to permit
1054                         // `[..a, b]` where `b` is a move, because in
1055                         // that case we can adjust the length of the
1056                         // original vec accordingly, but we'd have to
1057                         // make trans do the right thing, and it would
1058                         // only work for `Box<[T]>`s. It seems simpler
1059                         // to just require that people call
1060                         // `vec.pop()` or `vec.unshift()`.
1061                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
1062                         delegate.borrow(pat.id, pat.span,
1063                                         slice_cmt, slice_r,
1064                                         slice_bk, RefBinding);
1065                     }
1066                     _ => { }
1067                 }
1068             }
1069         }));
1070
1071         // Do a second pass over the pattern, calling `matched_pat` on
1072         // the interior nodes (enum variants and structs), as opposed
1073         // to the above loop's visit of than the bindings that form
1074         // the leaves of the pattern tree structure.
1075         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
1076             let def_map = def_map.borrow();
1077             let tcx = typer.tcx;
1078
1079             match pat.node {
1080                 hir::PatEnum(_, _) | hir::PatQPath(..) |
1081                 hir::PatIdent(_, _, None) | hir::PatStruct(..) => {
1082                     match def_map.get(&pat.id).map(|d| d.full_def()) {
1083                         None => {
1084                             // no definition found: pat is not a
1085                             // struct or enum pattern.
1086                         }
1087
1088                         Some(def::DefVariant(enum_did, variant_did, _is_struct)) => {
1089                             let downcast_cmt =
1090                                 if tcx.lookup_adt_def(enum_did).is_univariant() {
1091                                     cmt_pat
1092                                 } else {
1093                                     let cmt_pat_ty = cmt_pat.ty;
1094                                     mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1095                                 };
1096
1097                             debug!("variant downcast_cmt={:?} pat={:?}",
1098                                    downcast_cmt,
1099                                    pat);
1100
1101                             delegate.matched_pat(pat, downcast_cmt, match_mode);
1102                         }
1103
1104                         Some(def::DefStruct(..)) | Some(def::DefTy(_, false)) => {
1105                             // A struct (in either the value or type
1106                             // namespace; we encounter the former on
1107                             // e.g. patterns for unit structs).
1108
1109                             debug!("struct cmt_pat={:?} pat={:?}",
1110                                    cmt_pat,
1111                                    pat);
1112
1113                             delegate.matched_pat(pat, cmt_pat, match_mode);
1114                         }
1115
1116                         Some(def::DefConst(..)) |
1117                         Some(def::DefAssociatedConst(..)) |
1118                         Some(def::DefLocal(..)) => {
1119                             // This is a leaf (i.e. identifier binding
1120                             // or constant value to match); thus no
1121                             // `matched_pat` call.
1122                         }
1123
1124                         Some(def @ def::DefTy(_, true)) => {
1125                             // An enum's type -- should never be in a
1126                             // pattern.
1127
1128                             if !tcx.sess.has_errors() {
1129                                 let msg = format!("Pattern has unexpected type: {:?} and type {:?}",
1130                                                   def,
1131                                                   cmt_pat.ty);
1132                                 tcx.sess.span_bug(pat.span, &msg)
1133                             }
1134                         }
1135
1136                         Some(def) => {
1137                             // Remaining cases are e.g. DefFn, to
1138                             // which identifiers within patterns
1139                             // should not resolve. However, we do
1140                             // encouter this when using the
1141                             // expr-use-visitor during typeck. So just
1142                             // ignore it, an error should have been
1143                             // reported.
1144
1145                             if !tcx.sess.has_errors() {
1146                                 let msg = format!("Pattern has unexpected def: {:?} and type {:?}",
1147                                                   def,
1148                                                   cmt_pat.ty);
1149                                 tcx.sess.span_bug(pat.span, &msg[..])
1150                             }
1151                         }
1152                     }
1153                 }
1154
1155                 hir::PatIdent(_, _, Some(_)) => {
1156                     // Do nothing; this is a binding (not a enum
1157                     // variant or struct), and the cat_pattern call
1158                     // will visit the substructure recursively.
1159                 }
1160
1161                 hir::PatWild(_) | hir::PatTup(..) | hir::PatBox(..) |
1162                 hir::PatRegion(..) | hir::PatLit(..) | hir::PatRange(..) |
1163                 hir::PatVec(..) => {
1164                     // Similarly, each of these cases does not
1165                     // correspond to a enum variant or struct, so we
1166                     // do not do any `matched_pat` calls for these
1167                     // cases either.
1168                 }
1169             }
1170         }));
1171     }
1172
1173     fn walk_captures(&mut self, closure_expr: &hir::Expr) {
1174         debug!("walk_captures({:?})", closure_expr);
1175
1176         self.tcx().with_freevars(closure_expr.id, |freevars| {
1177             for freevar in freevars {
1178                 let id_var = freevar.def.def_id().node;
1179                 let upvar_id = ty::UpvarId { var_id: id_var,
1180                                              closure_expr_id: closure_expr.id };
1181                 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
1182                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1183                                                                    closure_expr.span,
1184                                                                    freevar.def));
1185                 match upvar_capture {
1186                     ty::UpvarCapture::ByValue => {
1187                         let mode = copy_or_move(self.typer, &cmt_var, CaptureMove);
1188                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1189                     }
1190                     ty::UpvarCapture::ByRef(upvar_borrow) => {
1191                         self.delegate.borrow(closure_expr.id,
1192                                              closure_expr.span,
1193                                              cmt_var,
1194                                              upvar_borrow.region,
1195                                              upvar_borrow.kind,
1196                                              ClosureCapture(freevar.span));
1197                     }
1198                 }
1199             }
1200         });
1201     }
1202
1203     fn cat_captured_var(&mut self,
1204                         closure_id: ast::NodeId,
1205                         closure_span: Span,
1206                         upvar_def: def::Def)
1207                         -> mc::McResult<mc::cmt<'tcx>> {
1208         // Create the cmt for the variable being borrowed, from the
1209         // caller's perspective
1210         let var_id = upvar_def.def_id().node;
1211         let var_ty = try!(self.typer.node_ty(var_id));
1212         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1213     }
1214 }
1215
1216 fn copy_or_move<'a, 'tcx>(typer: &infer::InferCtxt<'a, 'tcx>,
1217                       cmt: &mc::cmt<'tcx>,
1218                       move_reason: MoveReason)
1219                       -> ConsumeMode
1220 {
1221     if typer.type_moves_by_default(cmt.ty, cmt.span) {
1222         Move(move_reason)
1223     } else {
1224         Copy
1225     }
1226 }