src/librustc/middle/expr_use_visitor.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A different sort of visitor for walking fn bodies.  Unlike the
  12 //! normal visitor, which just walks the entire body in one shot, the
  13 //! `ExprUseVisitor` determines how expressions are being used.
  14
  15 pub use self::LoanCause::*;
  16 pub use self::ConsumeMode::*;
  17 pub use self::MoveReason::*;
  18 pub use self::MatchMode::*;
  19 use self::TrackMatchMode::*;
  20 use self::OverloadedCallType::*;
  21
  22 use hir::def::Def;
  23 use hir::def_id::{DefId};
  24 use infer::InferCtxt;
  25 use middle::mem_categorization as mc;
  26 use middle::region::RegionMaps;
  27 use ty::{self, TyCtxt, adjustment};
  28
  29 use hir::{self, PatKind};
  30
  31 use syntax::ast;
  32 use syntax::ptr::P;
  33 use syntax_pos::Span;
  34
  35 ///////////////////////////////////////////////////////////////////////////
  36 // The Delegate trait
  37
  38 /// This trait defines the callbacks you can expect to receive when
  39 /// employing the ExprUseVisitor.
  40 pub trait Delegate<'tcx> {
  41     // The value found at `cmt` is either copied or moved, depending
  42     // on mode.
  43     fn consume(&mut self,
  44                consume_id: ast::NodeId,
  45                consume_span: Span,
  46                cmt: mc::cmt<'tcx>,
  47                mode: ConsumeMode);
  48
  49     // The value found at `cmt` has been determined to match the
  50     // pattern binding `matched_pat`, and its subparts are being
  51     // copied or moved depending on `mode`.  Note that `matched_pat`
  52     // is called on all variant/structs in the pattern (i.e., the
  53     // interior nodes of the pattern's tree structure) while
  54     // consume_pat is called on the binding identifiers in the pattern
  55     // (which are leaves of the pattern's tree structure).
  56     //
  57     // Note that variants/structs and identifiers are disjoint; thus
  58     // `matched_pat` and `consume_pat` are never both called on the
  59     // same input pattern structure (though of `consume_pat` can be
  60     // called on a subpart of an input passed to `matched_pat).
  61     fn matched_pat(&mut self,
  62                    matched_pat: &hir::Pat,
  63                    cmt: mc::cmt<'tcx>,
  64                    mode: MatchMode);
  65
  66     // The value found at `cmt` is either copied or moved via the
  67     // pattern binding `consume_pat`, depending on mode.
  68     fn consume_pat(&mut self,
  69                    consume_pat: &hir::Pat,
  70                    cmt: mc::cmt<'tcx>,
  71                    mode: ConsumeMode);
  72
  73     // The value found at `borrow` is being borrowed at the point
  74     // `borrow_id` for the region `loan_region` with kind `bk`.
  75     fn borrow(&mut self,
  76               borrow_id: ast::NodeId,
  77               borrow_span: Span,
  78               cmt: mc::cmt<'tcx>,
  79               loan_region: ty::Region<'tcx>,
  80               bk: ty::BorrowKind,
  81               loan_cause: LoanCause);
  82
  83     // The local variable `id` is declared but not initialized.
  84     fn decl_without_init(&mut self,
  85                          id: ast::NodeId,
  86                          span: Span);
  87
  88     // The path at `cmt` is being assigned to.
  89     fn mutate(&mut self,
  90               assignment_id: ast::NodeId,
  91               assignment_span: Span,
  92               assignee_cmt: mc::cmt<'tcx>,
  93               mode: MutateMode);
  94 }
  95
  96 #[derive(Copy, Clone, PartialEq, Debug)]
  97 pub enum LoanCause {
  98     ClosureCapture(Span),
  99     AddrOf,
 100     AutoRef,
 101     AutoUnsafe,
 102     RefBinding,
 103     OverloadedOperator,
 104     ClosureInvocation,
 105     ForLoop,
 106     MatchDiscriminant
 107 }
 108
 109 #[derive(Copy, Clone, PartialEq, Debug)]
 110 pub enum ConsumeMode {
 111     Copy,                // reference to x where x has a type that copies
 112     Move(MoveReason),    // reference to x where x has a type that moves
 113 }
 114
 115 #[derive(Copy, Clone, PartialEq, Debug)]
 116 pub enum MoveReason {
 117     DirectRefMove,
 118     PatBindingMove,
 119     CaptureMove,
 120 }
 121
 122 #[derive(Copy, Clone, PartialEq, Debug)]
 123 pub enum MatchMode {
 124     NonBindingMatch,
 125     BorrowingMatch,
 126     CopyingMatch,
 127     MovingMatch,
 128 }
 129
 130 #[derive(Copy, Clone, PartialEq, Debug)]
 131 enum TrackMatchMode {
 132     Unknown,
 133     Definite(MatchMode),
 134     Conflicting,
 135 }
 136
 137 impl TrackMatchMode {
 138     // Builds up the whole match mode for a pattern from its constituent
 139     // parts.  The lattice looks like this:
 140     //
 141     //          Conflicting
 142     //            /     \
 143     //           /       \
 144     //      Borrowing   Moving
 145     //           \       /
 146     //            \     /
 147     //            Copying
 148     //               |
 149     //          NonBinding
 150     //               |
 151     //            Unknown
 152     //
 153     // examples:
 154     //
 155     // * `(_, some_int)` pattern is Copying, since
 156     //   NonBinding + Copying => Copying
 157     //
 158     // * `(some_int, some_box)` pattern is Moving, since
 159     //   Copying + Moving => Moving
 160     //
 161     // * `(ref x, some_box)` pattern is Conflicting, since
 162     //   Borrowing + Moving => Conflicting
 163     //
 164     // Note that the `Unknown` and `Conflicting` states are
 165     // represented separately from the other more interesting
 166     // `Definite` states, which simplifies logic here somewhat.
 167     fn lub(&mut self, mode: MatchMode) {
 168         *self = match (*self, mode) {
 169             // Note that clause order below is very significant.
 170             (Unknown, new) => Definite(new),
 171             (Definite(old), new) if old == new => Definite(old),
 172
 173             (Definite(old), NonBindingMatch) => Definite(old),
 174             (Definite(NonBindingMatch), new) => Definite(new),
 175
 176             (Definite(old), CopyingMatch) => Definite(old),
 177             (Definite(CopyingMatch), new) => Definite(new),
 178
 179             (Definite(_), _) => Conflicting,
 180             (Conflicting, _) => *self,
 181         };
 182     }
 183
 184     fn match_mode(&self) -> MatchMode {
 185         match *self {
 186             Unknown => NonBindingMatch,
 187             Definite(mode) => mode,
 188             Conflicting => {
 189                 // Conservatively return MovingMatch to let the
 190                 // compiler continue to make progress.
 191                 MovingMatch
 192             }
 193         }
 194     }
 195 }
 196
 197 #[derive(Copy, Clone, PartialEq, Debug)]
 198 pub enum MutateMode {
 199     Init,
 200     JustWrite,    // x = y
 201     WriteAndRead, // x += y
 202 }
 203
 204 #[derive(Copy, Clone)]
 205 enum OverloadedCallType {
 206     FnOverloadedCall,
 207     FnMutOverloadedCall,
 208     FnOnceOverloadedCall,
 209 }
 210
 211 impl OverloadedCallType {
 212     fn from_trait_id(tcx: TyCtxt, trait_id: DefId) -> OverloadedCallType {
 213         for &(maybe_function_trait, overloaded_call_type) in &[
 214             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 215             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 216             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 217         ] {
 218             match maybe_function_trait {
 219                 Some(function_trait) if function_trait == trait_id => {
 220                     return overloaded_call_type
 221                 }
 222                 _ => continue,
 223             }
 224         }
 225
 226         bug!("overloaded call didn't map to known function trait")
 227     }
 228
 229     fn from_method_id(tcx: TyCtxt, method_id: DefId) -> OverloadedCallType {
 230         let method = tcx.associated_item(method_id);
 231         OverloadedCallType::from_trait_id(tcx, method.container.id())
 232     }
 233 }
 234
 235 ///////////////////////////////////////////////////////////////////////////
 236 // The ExprUseVisitor type
 237 //
 238 // This is the code that actually walks the tree. Like
 239 // mem_categorization, it requires a TYPER, which is a type that
 240 // supplies types from the tree. After type checking is complete, you
 241 // can just use the tcx as the typer.
 242 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 243     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 244     delegate: &'a mut Delegate<'tcx>,
 245 }
 246
 247 // If the TYPER results in an error, it's because the type check
 248 // failed (or will fail, when the error is uncovered and reported
 249 // during writeback). In this case, we just ignore this part of the
 250 // code.
 251 //
 252 // Note that this macro appears similar to try!(), but, unlike try!(),
 253 // it does not propagate the error.
 254 macro_rules! return_if_err {
 255     ($inp: expr) => (
 256         match $inp {
 257             Ok(v) => v,
 258             Err(()) => {
 259                 debug!("mc reported err");
 260                 return
 261             }
 262         }
 263     )
 264 }
 265
 266 /// Whether the elements of an overloaded operation are passed by value or by reference
 267 enum PassArgs {
 268     ByValue,
 269     ByRef,
 270 }
 271
 272 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 273     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 274                region_maps: &'a RegionMaps,
 275                infcx: &'a InferCtxt<'a, 'gcx, 'tcx>)
 276                -> Self
 277     {
 278         ExprUseVisitor::with_options(delegate,
 279                                      infcx,
 280                                      region_maps,
 281                                      mc::MemCategorizationOptions::default())
 282     }
 283
 284     pub fn with_options(delegate: &'a mut (Delegate<'tcx>+'a),
 285                         infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 286                         region_maps: &'a RegionMaps,
 287                         options: mc::MemCategorizationOptions)
 288                -> Self
 289     {
 290         ExprUseVisitor {
 291             mc: mc::MemCategorizationContext::with_options(infcx, region_maps, options),
 292             delegate: delegate
 293         }
 294     }
 295
 296     pub fn consume_body(&mut self, body: &hir::Body) {
 297         debug!("consume_body(body={:?})", body);
 298
 299         for arg in &body.arguments {
 300             let arg_ty = return_if_err!(self.mc.infcx.node_ty(arg.pat.id));
 301
 302             let fn_body_scope_r = self.tcx().node_scope_region(body.value.id);
 303             let arg_cmt = self.mc.cat_rvalue(
 304                 arg.id,
 305                 arg.pat.span,
 306                 fn_body_scope_r, // Args live only as long as the fn body.
 307                 fn_body_scope_r,
 308                 arg_ty);
 309
 310             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 311         }
 312
 313         self.consume_expr(&body.value);
 314     }
 315
 316     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 317         self.mc.infcx.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.mc.infcx, &cmt, DirectRefMove);
 328         self.delegate.consume(consume_id, consume_span, cmt, mode);
 329     }
 330
 331     fn consume_exprs(&mut self, exprs: &[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<'tcx>,
 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         self.walk_expr(expr)
 366     }
 367
 368     fn select_from_expr(&mut self, expr: &hir::Expr) {
 369         self.walk_expr(expr)
 370     }
 371
 372     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 373         debug!("walk_expr(expr={:?})", expr);
 374
 375         self.walk_adjustment(expr);
 376
 377         match expr.node {
 378             hir::ExprPath(_) => { }
 379
 380             hir::ExprType(ref subexpr, _) => {
 381                 self.walk_expr(&subexpr)
 382             }
 383
 384             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 385                 if !self.walk_overloaded_operator(expr, &base, Vec::new(), PassArgs::ByRef) {
 386                     self.select_from_expr(&base);
 387                 }
 388             }
 389
 390             hir::ExprField(ref base, _) => {         // base.f
 391                 self.select_from_expr(&base);
 392             }
 393
 394             hir::ExprTupField(ref base, _) => {         // base.<n>
 395                 self.select_from_expr(&base);
 396             }
 397
 398             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 399                 if !self.walk_overloaded_operator(expr,
 400                                                   &lhs,
 401                                                   vec![&rhs],
 402                                                   PassArgs::ByValue) {
 403                     self.select_from_expr(&lhs);
 404                     self.consume_expr(&rhs);
 405                 }
 406             }
 407
 408             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 409                 self.walk_callee(expr, &callee);
 410                 self.consume_exprs(args);
 411             }
 412
 413             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 414                 self.consume_exprs(args);
 415             }
 416
 417             hir::ExprStruct(_, ref fields, ref opt_with) => {
 418                 self.walk_struct_expr(fields, opt_with);
 419             }
 420
 421             hir::ExprTup(ref exprs) => {
 422                 self.consume_exprs(exprs);
 423             }
 424
 425             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 426                 self.consume_expr(&cond_expr);
 427                 self.walk_expr(&then_expr);
 428                 if let Some(ref else_expr) = *opt_else_expr {
 429                     self.consume_expr(&else_expr);
 430                 }
 431             }
 432
 433             hir::ExprMatch(ref discr, ref arms, _) => {
 434                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 435                 let r = self.tcx().types.re_empty;
 436                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 437
 438                 // treatment of the discriminant is handled while walking the arms.
 439                 for arm in arms {
 440                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 441                     let mode = mode.match_mode();
 442                     self.walk_arm(discr_cmt.clone(), arm, mode);
 443                 }
 444             }
 445
 446             hir::ExprArray(ref exprs) => {
 447                 self.consume_exprs(exprs);
 448             }
 449
 450             hir::ExprAddrOf(m, ref base) => {   // &base
 451                 // make sure that the thing we are pointing out stays valid
 452                 // for the lifetime `scope_r` of the resulting ptr:
 453                 let expr_ty = return_if_err!(self.mc.infcx.node_ty(expr.id));
 454                 if let ty::TyRef(r, _) = expr_ty.sty {
 455                     let bk = ty::BorrowKind::from_mutbl(m);
 456                     self.borrow_expr(&base, r, bk, AddrOf);
 457                 }
 458             }
 459
 460             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 461                 for (o, output) in ia.outputs.iter().zip(outputs) {
 462                     if o.is_indirect {
 463                         self.consume_expr(output);
 464                     } else {
 465                         self.mutate_expr(expr, output,
 466                                          if o.is_rw {
 467                                              MutateMode::WriteAndRead
 468                                          } else {
 469                                              MutateMode::JustWrite
 470                                          });
 471                     }
 472                 }
 473                 self.consume_exprs(inputs);
 474             }
 475
 476             hir::ExprAgain(..) |
 477             hir::ExprLit(..) => {}
 478
 479             hir::ExprLoop(ref blk, _, _) => {
 480                 self.walk_block(&blk);
 481             }
 482
 483             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 484                 self.consume_expr(&cond_expr);
 485                 self.walk_block(&blk);
 486             }
 487
 488             hir::ExprUnary(op, ref lhs) => {
 489                 let pass_args = if op.is_by_value() {
 490                     PassArgs::ByValue
 491                 } else {
 492                     PassArgs::ByRef
 493                 };
 494
 495                 if !self.walk_overloaded_operator(expr, &lhs, Vec::new(), pass_args) {
 496                     self.consume_expr(&lhs);
 497                 }
 498             }
 499
 500             hir::ExprBinary(op, ref lhs, ref rhs) => {
 501                 let pass_args = if op.node.is_by_value() {
 502                     PassArgs::ByValue
 503                 } else {
 504                     PassArgs::ByRef
 505                 };
 506
 507                 if !self.walk_overloaded_operator(expr, &lhs, vec![&rhs], pass_args) {
 508                     self.consume_expr(&lhs);
 509                     self.consume_expr(&rhs);
 510                 }
 511             }
 512
 513             hir::ExprBlock(ref blk) => {
 514                 self.walk_block(&blk);
 515             }
 516
 517             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 518                 if let Some(ref expr) = *opt_expr {
 519                     self.consume_expr(&expr);
 520                 }
 521             }
 522
 523             hir::ExprAssign(ref lhs, ref rhs) => {
 524                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 525                 self.consume_expr(&rhs);
 526             }
 527
 528             hir::ExprCast(ref base, _) => {
 529                 self.consume_expr(&base);
 530             }
 531
 532             hir::ExprAssignOp(op, ref lhs, ref rhs) => {
 533                 // NB All our assignment operations take the RHS by value
 534                 assert!(op.node.is_by_value());
 535
 536                 if !self.walk_overloaded_operator(expr, lhs, vec![rhs], PassArgs::ByValue) {
 537                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 538                     self.consume_expr(&rhs);
 539                 }
 540             }
 541
 542             hir::ExprRepeat(ref base, _) => {
 543                 self.consume_expr(&base);
 544             }
 545
 546             hir::ExprClosure(.., fn_decl_span) => {
 547                 self.walk_captures(expr, fn_decl_span)
 548             }
 549
 550             hir::ExprBox(ref base) => {
 551                 self.consume_expr(&base);
 552             }
 553         }
 554     }
 555
 556     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 557         let callee_ty = return_if_err!(self.mc.infcx.expr_ty_adjusted(callee));
 558         debug!("walk_callee: callee={:?} callee_ty={:?}",
 559                callee, callee_ty);
 560         match callee_ty.sty {
 561             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 562                 self.consume_expr(callee);
 563             }
 564             ty::TyError => { }
 565             _ => {
 566                 let overloaded_call_type =
 567                     match self.mc.infcx.node_method_id(ty::MethodCall::expr(call.id)) {
 568                         Some(method_id) => {
 569                             OverloadedCallType::from_method_id(self.tcx(), method_id)
 570                         }
 571                         None => {
 572                             span_bug!(
 573                                 callee.span,
 574                                 "unexpected callee type {}",
 575                                 callee_ty)
 576                         }
 577                     };
 578                 match overloaded_call_type {
 579                     FnMutOverloadedCall => {
 580                         let call_scope_r = self.tcx().node_scope_region(call.id);
 581                         self.borrow_expr(callee,
 582                                          call_scope_r,
 583                                          ty::MutBorrow,
 584                                          ClosureInvocation);
 585                     }
 586                     FnOverloadedCall => {
 587                         let call_scope_r = self.tcx().node_scope_region(call.id);
 588                         self.borrow_expr(callee,
 589                                          call_scope_r,
 590                                          ty::ImmBorrow,
 591                                          ClosureInvocation);
 592                     }
 593                     FnOnceOverloadedCall => self.consume_expr(callee),
 594                 }
 595             }
 596         }
 597     }
 598
 599     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 600         match stmt.node {
 601             hir::StmtDecl(ref decl, _) => {
 602                 match decl.node {
 603                     hir::DeclLocal(ref local) => {
 604                         self.walk_local(&local);
 605                     }
 606
 607                     hir::DeclItem(_) => {
 608                         // we don't visit nested items in this visitor,
 609                         // only the fn body we were given.
 610                     }
 611                 }
 612             }
 613
 614             hir::StmtExpr(ref expr, _) |
 615             hir::StmtSemi(ref expr, _) => {
 616                 self.consume_expr(&expr);
 617             }
 618         }
 619     }
 620
 621     fn walk_local(&mut self, local: &hir::Local) {
 622         match local.init {
 623             None => {
 624                 let delegate = &mut self.delegate;
 625                 local.pat.each_binding(|_, id, span, _| {
 626                     delegate.decl_without_init(id, span);
 627                 })
 628             }
 629
 630             Some(ref expr) => {
 631                 // Variable declarations with
 632                 // initializers are considered
 633                 // "assigns", which is handled by
 634                 // `walk_pat`:
 635                 self.walk_expr(&expr);
 636                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 637                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 638             }
 639         }
 640     }
 641
 642     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 643     /// depending on its type.
 644     fn walk_block(&mut self, blk: &hir::Block) {
 645         debug!("walk_block(blk.id={})", blk.id);
 646
 647         for stmt in &blk.stmts {
 648             self.walk_stmt(stmt);
 649         }
 650
 651         if let Some(ref tail_expr) = blk.expr {
 652             self.consume_expr(&tail_expr);
 653         }
 654     }
 655
 656     fn walk_struct_expr(&mut self,
 657                         fields: &[hir::Field],
 658                         opt_with: &Option<P<hir::Expr>>) {
 659         // Consume the expressions supplying values for each field.
 660         for field in fields {
 661             self.consume_expr(&field.expr);
 662         }
 663
 664         let with_expr = match *opt_with {
 665             Some(ref w) => &**w,
 666             None => { return; }
 667         };
 668
 669         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 670
 671         // Select just those fields of the `with`
 672         // expression that will actually be used
 673         match with_cmt.ty.sty {
 674             ty::TyAdt(adt, substs) if adt.is_struct() => {
 675                 // Consume those fields of the with expression that are needed.
 676                 for with_field in &adt.struct_variant().fields {
 677                     if !contains_field_named(with_field, fields) {
 678                         let cmt_field = self.mc.cat_field(
 679                             &*with_expr,
 680                             with_cmt.clone(),
 681                             with_field.name,
 682                             with_field.ty(self.tcx(), substs)
 683                         );
 684                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 685                     }
 686                 }
 687             }
 688             _ => {
 689                 // the base expression should always evaluate to a
 690                 // struct; however, when EUV is run during typeck, it
 691                 // may not. This will generate an error earlier in typeck,
 692                 // so we can just ignore it.
 693                 if !self.tcx().sess.has_errors() {
 694                     span_bug!(
 695                         with_expr.span,
 696                         "with expression doesn't evaluate to a struct");
 697                 }
 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 infcx = self.mc.infcx;
 719         //NOTE(@jroesch): mixed RefCell borrow causes crash
 720         let adj = infcx.tables.borrow().adjustments.get(&expr.id).map(|x| x.clone());
 721         if let Some(adjustment) = adj {
 722             match adjustment.kind {
 723                 adjustment::Adjust::NeverToAny |
 724                 adjustment::Adjust::ReifyFnPointer |
 725                 adjustment::Adjust::UnsafeFnPointer |
 726                 adjustment::Adjust::ClosureFnPointer |
 727                 adjustment::Adjust::MutToConstPointer => {
 728                     // Creating a closure/fn-pointer or unsizing consumes
 729                     // the input and stores it into the resulting rvalue.
 730                     debug!("walk_adjustment: trivial adjustment");
 731                     let cmt_unadjusted =
 732                         return_if_err!(self.mc.cat_expr_unadjusted(expr));
 733                     self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 734                 }
 735                 adjustment::Adjust::DerefRef { autoderefs, autoref, unsize } => {
 736                     debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 737
 738                     self.walk_autoderefs(expr, autoderefs);
 739
 740                     let cmt_derefd =
 741                         return_if_err!(self.mc.cat_expr_autoderefd(expr, autoderefs));
 742
 743                     let cmt_refd =
 744                         self.walk_autoref(expr, cmt_derefd, autoref);
 745
 746                     if unsize {
 747                         // Unsizing consumes the thin pointer and produces a fat one.
 748                         self.delegate_consume(expr.id, expr.span, cmt_refd);
 749                     }
 750                 }
 751             }
 752         }
 753     }
 754
 755     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 756     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 757     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 758     fn walk_autoderefs(&mut self,
 759                        expr: &hir::Expr,
 760                        autoderefs: usize) {
 761         debug!("walk_autoderefs expr={:?} autoderefs={}", expr, autoderefs);
 762
 763         for i in 0..autoderefs {
 764             let deref_id = ty::MethodCall::autoderef(expr.id, i as u32);
 765             if let Some(method_ty) = self.mc.infcx.node_method_ty(deref_id) {
 766                 let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 767
 768                 // the method call infrastructure should have
 769                 // replaced all late-bound regions with variables:
 770                 let self_ty = method_ty.fn_sig().input(0);
 771                 let self_ty = self.tcx().no_late_bound_regions(&self_ty).unwrap();
 772
 773                 let (m, r) = match self_ty.sty {
 774                     ty::TyRef(r, ref m) => (m.mutbl, r),
 775                     _ => span_bug!(expr.span,
 776                                    "bad overloaded deref type {:?}",
 777                                    method_ty)
 778                 };
 779                 let bk = ty::BorrowKind::from_mutbl(m);
 780                 self.delegate.borrow(expr.id, expr.span, cmt,
 781                                      r, bk, AutoRef);
 782             }
 783         }
 784     }
 785
 786     /// Walks the autoref `opt_autoref` applied to the autoderef'd
 787     /// `expr`. `cmt_derefd` is the mem-categorized form of `expr`
 788     /// after all relevant autoderefs have occurred. Because AutoRefs
 789     /// can be recursive, this function is recursive: it first walks
 790     /// deeply all the way down the autoref chain, and then processes
 791     /// the autorefs on the way out. At each point, it returns the
 792     /// `cmt` for the rvalue that will be produced by introduced an
 793     /// autoref.
 794     fn walk_autoref(&mut self,
 795                     expr: &hir::Expr,
 796                     cmt_base: mc::cmt<'tcx>,
 797                     opt_autoref: Option<adjustment::AutoBorrow<'tcx>>)
 798                     -> mc::cmt<'tcx>
 799     {
 800         debug!("walk_autoref(expr.id={} cmt_derefd={:?} opt_autoref={:?})",
 801                expr.id,
 802                cmt_base,
 803                opt_autoref);
 804
 805         let cmt_base_ty = cmt_base.ty;
 806
 807         let autoref = match opt_autoref {
 808             Some(ref autoref) => autoref,
 809             None => {
 810                 // No AutoRef.
 811                 return cmt_base;
 812             }
 813         };
 814
 815         match *autoref {
 816             adjustment::AutoBorrow::Ref(r, m) => {
 817                 self.delegate.borrow(expr.id,
 818                                      expr.span,
 819                                      cmt_base,
 820                                      r,
 821                                      ty::BorrowKind::from_mutbl(m),
 822                                      AutoRef);
 823             }
 824
 825             adjustment::AutoBorrow::RawPtr(m) => {
 826                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 827                        expr.id,
 828                        cmt_base);
 829
 830                 // Converting from a &T to *T (or &mut T to *mut T) is
 831                 // treated as borrowing it for the enclosing temporary
 832                 // scope.
 833                 let r = self.tcx().node_scope_region(expr.id);
 834
 835                 self.delegate.borrow(expr.id,
 836                                      expr.span,
 837                                      cmt_base,
 838                                      r,
 839                                      ty::BorrowKind::from_mutbl(m),
 840                                      AutoUnsafe);
 841             }
 842         }
 843
 844         // Construct the categorization for the result of the autoref.
 845         // This is always an rvalue, since we are producing a new
 846         // (temporary) indirection.
 847
 848         let adj_ty = cmt_base_ty.adjust_for_autoref(self.tcx(), opt_autoref);
 849
 850         self.mc.cat_rvalue_node(expr.id, expr.span, adj_ty)
 851     }
 852
 853
 854     // When this returns true, it means that the expression *is* a
 855     // method-call (i.e. via the operator-overload).  This true result
 856     // also implies that walk_overloaded_operator already took care of
 857     // recursively processing the input arguments, and thus the caller
 858     // should not do so.
 859     fn walk_overloaded_operator(&mut self,
 860                                 expr: &hir::Expr,
 861                                 receiver: &hir::Expr,
 862                                 rhs: Vec<&hir::Expr>,
 863                                 pass_args: PassArgs)
 864                                 -> bool
 865     {
 866         if !self.mc.infcx.is_method_call(expr.id) {
 867             return false;
 868         }
 869
 870         match pass_args {
 871             PassArgs::ByValue => {
 872                 self.consume_expr(receiver);
 873                 for &arg in &rhs {
 874                     self.consume_expr(arg);
 875                 }
 876
 877                 return true;
 878             },
 879             PassArgs::ByRef => {},
 880         }
 881
 882         self.walk_expr(receiver);
 883
 884         // Arguments (but not receivers) to overloaded operator
 885         // methods are implicitly autoref'd which sadly does not use
 886         // adjustments, so we must hardcode the borrow here.
 887
 888         let r = self.tcx().node_scope_region(expr.id);
 889         let bk = ty::ImmBorrow;
 890
 891         for &arg in &rhs {
 892             self.borrow_expr(arg, r, bk, OverloadedOperator);
 893         }
 894         return true;
 895     }
 896
 897     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 898         let mut mode = Unknown;
 899         for pat in &arm.pats {
 900             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 901         }
 902         mode
 903     }
 904
 905     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 906         for pat in &arm.pats {
 907             self.walk_pat(discr_cmt.clone(), &pat, mode);
 908         }
 909
 910         if let Some(ref guard) = arm.guard {
 911             self.consume_expr(&guard);
 912         }
 913
 914         self.consume_expr(&arm.body);
 915     }
 916
 917     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 918     /// arg or let binding.  *Not* a match arm or nested pat.)
 919     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 920         let mut mode = Unknown;
 921         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 922         let mode = mode.match_mode();
 923         self.walk_pat(cmt_discr, pat, mode);
 924     }
 925
 926     /// Identifies any bindings within `pat` and accumulates within
 927     /// `mode` whether the overall pattern/match structure is a move,
 928     /// copy, or borrow.
 929     fn determine_pat_move_mode(&mut self,
 930                                cmt_discr: mc::cmt<'tcx>,
 931                                pat: &hir::Pat,
 932                                mode: &mut TrackMatchMode) {
 933         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 934                pat);
 935         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 936             match pat.node {
 937                 PatKind::Binding(hir::BindByRef(..), ..) =>
 938                     mode.lub(BorrowingMatch),
 939                 PatKind::Binding(hir::BindByValue(..), ..) => {
 940                     match copy_or_move(self.mc.infcx, &cmt_pat, PatBindingMove) {
 941                         Copy => mode.lub(CopyingMatch),
 942                         Move(..) => mode.lub(MovingMatch),
 943                     }
 944                 }
 945                 _ => {}
 946             }
 947         }));
 948     }
 949
 950     /// The core driver for walking a pattern; `match_mode` must be
 951     /// established up front, e.g. via `determine_pat_move_mode` (see
 952     /// also `walk_irrefutable_pat` for patterns that stand alone).
 953     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 954         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 955
 956         let tcx = &self.tcx();
 957         let mc = &self.mc;
 958         let infcx = self.mc.infcx;
 959         let delegate = &mut self.delegate;
 960         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 961             if let PatKind::Binding(bmode, def_id, ..) = pat.node {
 962                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 963
 964                 // pat_ty: the type of the binding being produced.
 965                 let pat_ty = return_if_err!(infcx.node_ty(pat.id));
 966
 967                 // Each match binding is effectively an assignment to the
 968                 // binding being produced.
 969                 let def = Def::Local(def_id);
 970                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 971                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 972                 }
 973
 974                 // It is also a borrow or copy/move of the value being matched.
 975                 match bmode {
 976                     hir::BindByRef(m) => {
 977                         if let ty::TyRef(r, _) = pat_ty.sty {
 978                             let bk = ty::BorrowKind::from_mutbl(m);
 979                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 980                         }
 981                     }
 982                     hir::BindByValue(..) => {
 983                         let mode = copy_or_move(infcx, &cmt_pat, PatBindingMove);
 984                         debug!("walk_pat binding consuming pat");
 985                         delegate.consume_pat(pat, cmt_pat, mode);
 986                     }
 987                 }
 988             }
 989         }));
 990
 991         // Do a second pass over the pattern, calling `matched_pat` on
 992         // the interior nodes (enum variants and structs), as opposed
 993         // to the above loop's visit of than the bindings that form
 994         // the leaves of the pattern tree structure.
 995         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
 996             let qpath = match pat.node {
 997                 PatKind::Path(ref qpath) |
 998                 PatKind::TupleStruct(ref qpath, ..) |
 999                 PatKind::Struct(ref qpath, ..) => qpath,
1000                 _ => return
1001             };
1002             let def = infcx.tables.borrow().qpath_def(qpath, pat.id);
1003             match def {
1004                 Def::Variant(variant_did) |
1005                 Def::VariantCtor(variant_did, ..) => {
1006                     let enum_did = tcx.parent_def_id(variant_did).unwrap();
1007                     let downcast_cmt = if tcx.adt_def(enum_did).is_univariant() {
1008                         cmt_pat
1009                     } else {
1010                         let cmt_pat_ty = cmt_pat.ty;
1011                         mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1012                     };
1013
1014                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
1015                     delegate.matched_pat(pat, downcast_cmt, match_mode);
1016                 }
1017                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
1018                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
1019                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
1020                     delegate.matched_pat(pat, cmt_pat, match_mode);
1021                 }
1022                 _ => {}
1023             }
1024         }));
1025     }
1026
1027     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
1028         debug!("walk_captures({:?})", closure_expr);
1029
1030         self.tcx().with_freevars(closure_expr.id, |freevars| {
1031             for freevar in freevars {
1032                 let def_id = freevar.def.def_id();
1033                 let id_var = self.tcx().hir.as_local_node_id(def_id).unwrap();
1034                 let upvar_id = ty::UpvarId { var_id: id_var,
1035                                              closure_expr_id: closure_expr.id };
1036                 let upvar_capture = self.mc.infcx.upvar_capture(upvar_id).unwrap();
1037                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1038                                                                    fn_decl_span,
1039                                                                    freevar.def));
1040                 match upvar_capture {
1041                     ty::UpvarCapture::ByValue => {
1042                         let mode = copy_or_move(self.mc.infcx, &cmt_var, CaptureMove);
1043                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1044                     }
1045                     ty::UpvarCapture::ByRef(upvar_borrow) => {
1046                         self.delegate.borrow(closure_expr.id,
1047                                              fn_decl_span,
1048                                              cmt_var,
1049                                              upvar_borrow.region,
1050                                              upvar_borrow.kind,
1051                                              ClosureCapture(freevar.span));
1052                     }
1053                 }
1054             }
1055         });
1056     }
1057
1058     fn cat_captured_var(&mut self,
1059                         closure_id: ast::NodeId,
1060                         closure_span: Span,
1061                         upvar_def: Def)
1062                         -> mc::McResult<mc::cmt<'tcx>> {
1063         // Create the cmt for the variable being borrowed, from the
1064         // caller's perspective
1065         let var_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
1066         let var_ty = self.mc.infcx.node_ty(var_id)?;
1067         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1068     }
1069 }
1070
1071 fn copy_or_move<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
1072                                 cmt: &mc::cmt<'tcx>,
1073                                 move_reason: MoveReason)
1074                                 -> ConsumeMode
1075 {
1076     if infcx.type_moves_by_default(cmt.ty, cmt.span) {
1077         Move(move_reason)
1078     } else {
1079         Copy
1080     }
1081 }