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     param_env: ty::ParamEnv<'tcx>,
 246 }
 247
 248 // If the TYPER results in an error, it's because the type check
 249 // failed (or will fail, when the error is uncovered and reported
 250 // during writeback). In this case, we just ignore this part of the
 251 // code.
 252 //
 253 // Note that this macro appears similar to try!(), but, unlike try!(),
 254 // it does not propagate the error.
 255 macro_rules! return_if_err {
 256     ($inp: expr) => (
 257         match $inp {
 258             Ok(v) => v,
 259             Err(()) => {
 260                 debug!("mc reported err");
 261                 return
 262             }
 263         }
 264     )
 265 }
 266
 267 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 268     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 269                region_maps: &'a RegionMaps,
 270                infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 271                param_env: ty::ParamEnv<'tcx>)
 272                -> Self
 273     {
 274         ExprUseVisitor::with_options(delegate,
 275                                      infcx,
 276                                      param_env,
 277                                      region_maps,
 278                                      mc::MemCategorizationOptions::default())
 279     }
 280
 281     pub fn with_options(delegate: &'a mut (Delegate<'tcx>+'a),
 282                         infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 283                         param_env: ty::ParamEnv<'tcx>,
 284                         region_maps: &'a RegionMaps,
 285                         options: mc::MemCategorizationOptions)
 286                -> Self
 287     {
 288         ExprUseVisitor {
 289             mc: mc::MemCategorizationContext::with_options(infcx, region_maps, options),
 290             delegate,
 291             param_env,
 292         }
 293     }
 294
 295     pub fn consume_body(&mut self, body: &hir::Body) {
 296         debug!("consume_body(body={:?})", body);
 297
 298         for arg in &body.arguments {
 299             let arg_ty = return_if_err!(self.mc.infcx.node_ty(arg.pat.id));
 300
 301             let fn_body_scope_r = self.tcx().node_scope_region(body.value.id);
 302             let arg_cmt = self.mc.cat_rvalue(
 303                 arg.id,
 304                 arg.pat.span,
 305                 fn_body_scope_r, // Args live only as long as the fn body.
 306                 fn_body_scope_r,
 307                 arg_ty);
 308
 309             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 310         }
 311
 312         self.consume_expr(&body.value);
 313     }
 314
 315     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 316         self.mc.infcx.tcx
 317     }
 318
 319     fn delegate_consume(&mut self,
 320                         consume_id: ast::NodeId,
 321                         consume_span: Span,
 322                         cmt: mc::cmt<'tcx>) {
 323         debug!("delegate_consume(consume_id={}, cmt={:?})",
 324                consume_id, cmt);
 325
 326         let mode = copy_or_move(self.mc.infcx, self.param_env, &cmt, DirectRefMove);
 327         self.delegate.consume(consume_id, consume_span, cmt, mode);
 328     }
 329
 330     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 331         for expr in exprs {
 332             self.consume_expr(&expr);
 333         }
 334     }
 335
 336     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 337         debug!("consume_expr(expr={:?})", expr);
 338
 339         let cmt = return_if_err!(self.mc.cat_expr(expr));
 340         self.delegate_consume(expr.id, expr.span, cmt);
 341         self.walk_expr(expr);
 342     }
 343
 344     fn mutate_expr(&mut self,
 345                    assignment_expr: &hir::Expr,
 346                    expr: &hir::Expr,
 347                    mode: MutateMode) {
 348         let cmt = return_if_err!(self.mc.cat_expr(expr));
 349         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 350         self.walk_expr(expr);
 351     }
 352
 353     fn borrow_expr(&mut self,
 354                    expr: &hir::Expr,
 355                    r: ty::Region<'tcx>,
 356                    bk: ty::BorrowKind,
 357                    cause: LoanCause) {
 358         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 359                expr, r, bk);
 360
 361         let cmt = return_if_err!(self.mc.cat_expr(expr));
 362         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 363
 364         self.walk_expr(expr)
 365     }
 366
 367     fn select_from_expr(&mut self, expr: &hir::Expr) {
 368         self.walk_expr(expr)
 369     }
 370
 371     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 372         debug!("walk_expr(expr={:?})", expr);
 373
 374         self.walk_adjustment(expr);
 375
 376         match expr.node {
 377             hir::ExprPath(_) => { }
 378
 379             hir::ExprType(ref subexpr, _) => {
 380                 self.walk_expr(&subexpr)
 381             }
 382
 383             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 384                 self.select_from_expr(&base);
 385             }
 386
 387             hir::ExprField(ref base, _) => {         // base.f
 388                 self.select_from_expr(&base);
 389             }
 390
 391             hir::ExprTupField(ref base, _) => {         // base.<n>
 392                 self.select_from_expr(&base);
 393             }
 394
 395             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 396                 self.select_from_expr(&lhs);
 397                 self.consume_expr(&rhs);
 398             }
 399
 400             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 401                 self.walk_callee(expr, &callee);
 402                 self.consume_exprs(args);
 403             }
 404
 405             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 406                 self.consume_exprs(args);
 407             }
 408
 409             hir::ExprStruct(_, ref fields, ref opt_with) => {
 410                 self.walk_struct_expr(fields, opt_with);
 411             }
 412
 413             hir::ExprTup(ref exprs) => {
 414                 self.consume_exprs(exprs);
 415             }
 416
 417             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 418                 self.consume_expr(&cond_expr);
 419                 self.walk_expr(&then_expr);
 420                 if let Some(ref else_expr) = *opt_else_expr {
 421                     self.consume_expr(&else_expr);
 422                 }
 423             }
 424
 425             hir::ExprMatch(ref discr, ref arms, _) => {
 426                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 427                 let r = self.tcx().types.re_empty;
 428                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 429
 430                 // treatment of the discriminant is handled while walking the arms.
 431                 for arm in arms {
 432                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 433                     let mode = mode.match_mode();
 434                     self.walk_arm(discr_cmt.clone(), arm, mode);
 435                 }
 436             }
 437
 438             hir::ExprArray(ref exprs) => {
 439                 self.consume_exprs(exprs);
 440             }
 441
 442             hir::ExprAddrOf(m, ref base) => {   // &base
 443                 // make sure that the thing we are pointing out stays valid
 444                 // for the lifetime `scope_r` of the resulting ptr:
 445                 let expr_ty = return_if_err!(self.mc.infcx.node_ty(expr.id));
 446                 if let ty::TyRef(r, _) = expr_ty.sty {
 447                     let bk = ty::BorrowKind::from_mutbl(m);
 448                     self.borrow_expr(&base, r, bk, AddrOf);
 449                 }
 450             }
 451
 452             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 453                 for (o, output) in ia.outputs.iter().zip(outputs) {
 454                     if o.is_indirect {
 455                         self.consume_expr(output);
 456                     } else {
 457                         self.mutate_expr(expr, output,
 458                                          if o.is_rw {
 459                                              MutateMode::WriteAndRead
 460                                          } else {
 461                                              MutateMode::JustWrite
 462                                          });
 463                     }
 464                 }
 465                 self.consume_exprs(inputs);
 466             }
 467
 468             hir::ExprAgain(..) |
 469             hir::ExprLit(..) => {}
 470
 471             hir::ExprLoop(ref blk, _, _) => {
 472                 self.walk_block(&blk);
 473             }
 474
 475             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 476                 self.consume_expr(&cond_expr);
 477                 self.walk_block(&blk);
 478             }
 479
 480             hir::ExprUnary(_, ref lhs) => {
 481                 self.consume_expr(&lhs);
 482             }
 483
 484             hir::ExprBinary(_, ref lhs, ref rhs) => {
 485                 self.consume_expr(&lhs);
 486                 self.consume_expr(&rhs);
 487             }
 488
 489             hir::ExprBlock(ref blk) => {
 490                 self.walk_block(&blk);
 491             }
 492
 493             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 494                 if let Some(ref expr) = *opt_expr {
 495                     self.consume_expr(&expr);
 496                 }
 497             }
 498
 499             hir::ExprAssign(ref lhs, ref rhs) => {
 500                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 501                 self.consume_expr(&rhs);
 502             }
 503
 504             hir::ExprCast(ref base, _) => {
 505                 self.consume_expr(&base);
 506             }
 507
 508             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 509                 if self.mc.infcx.tables.borrow().is_method_call(expr) {
 510                     self.consume_expr(lhs);
 511                 } else {
 512                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 513                 }
 514                 self.consume_expr(&rhs);
 515             }
 516
 517             hir::ExprRepeat(ref base, _) => {
 518                 self.consume_expr(&base);
 519             }
 520
 521             hir::ExprClosure(.., fn_decl_span) => {
 522                 self.walk_captures(expr, fn_decl_span)
 523             }
 524
 525             hir::ExprBox(ref base) => {
 526                 self.consume_expr(&base);
 527             }
 528         }
 529     }
 530
 531     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 532         let callee_ty = return_if_err!(self.mc.infcx.expr_ty_adjusted(callee));
 533         debug!("walk_callee: callee={:?} callee_ty={:?}",
 534                callee, callee_ty);
 535         match callee_ty.sty {
 536             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 537                 self.consume_expr(callee);
 538             }
 539             ty::TyError => { }
 540             _ => {
 541                 let def_id = self.mc.infcx.tables.borrow().type_dependent_defs[&call.id].def_id();
 542                 match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 543                     FnMutOverloadedCall => {
 544                         let call_scope_r = self.tcx().node_scope_region(call.id);
 545                         self.borrow_expr(callee,
 546                                          call_scope_r,
 547                                          ty::MutBorrow,
 548                                          ClosureInvocation);
 549                     }
 550                     FnOverloadedCall => {
 551                         let call_scope_r = self.tcx().node_scope_region(call.id);
 552                         self.borrow_expr(callee,
 553                                          call_scope_r,
 554                                          ty::ImmBorrow,
 555                                          ClosureInvocation);
 556                     }
 557                     FnOnceOverloadedCall => self.consume_expr(callee),
 558                 }
 559             }
 560         }
 561     }
 562
 563     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 564         match stmt.node {
 565             hir::StmtDecl(ref decl, _) => {
 566                 match decl.node {
 567                     hir::DeclLocal(ref local) => {
 568                         self.walk_local(&local);
 569                     }
 570
 571                     hir::DeclItem(_) => {
 572                         // we don't visit nested items in this visitor,
 573                         // only the fn body we were given.
 574                     }
 575                 }
 576             }
 577
 578             hir::StmtExpr(ref expr, _) |
 579             hir::StmtSemi(ref expr, _) => {
 580                 self.consume_expr(&expr);
 581             }
 582         }
 583     }
 584
 585     fn walk_local(&mut self, local: &hir::Local) {
 586         match local.init {
 587             None => {
 588                 let delegate = &mut self.delegate;
 589                 local.pat.each_binding(|_, id, span, _| {
 590                     delegate.decl_without_init(id, span);
 591                 })
 592             }
 593
 594             Some(ref expr) => {
 595                 // Variable declarations with
 596                 // initializers are considered
 597                 // "assigns", which is handled by
 598                 // `walk_pat`:
 599                 self.walk_expr(&expr);
 600                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 601                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 602             }
 603         }
 604     }
 605
 606     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 607     /// depending on its type.
 608     fn walk_block(&mut self, blk: &hir::Block) {
 609         debug!("walk_block(blk.id={})", blk.id);
 610
 611         for stmt in &blk.stmts {
 612             self.walk_stmt(stmt);
 613         }
 614
 615         if let Some(ref tail_expr) = blk.expr {
 616             self.consume_expr(&tail_expr);
 617         }
 618     }
 619
 620     fn walk_struct_expr(&mut self,
 621                         fields: &[hir::Field],
 622                         opt_with: &Option<P<hir::Expr>>) {
 623         // Consume the expressions supplying values for each field.
 624         for field in fields {
 625             self.consume_expr(&field.expr);
 626         }
 627
 628         let with_expr = match *opt_with {
 629             Some(ref w) => &**w,
 630             None => { return; }
 631         };
 632
 633         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 634
 635         // Select just those fields of the `with`
 636         // expression that will actually be used
 637         match with_cmt.ty.sty {
 638             ty::TyAdt(adt, substs) if adt.is_struct() => {
 639                 // Consume those fields of the with expression that are needed.
 640                 for with_field in &adt.struct_variant().fields {
 641                     if !contains_field_named(with_field, fields) {
 642                         let cmt_field = self.mc.cat_field(
 643                             &*with_expr,
 644                             with_cmt.clone(),
 645                             with_field.name,
 646                             with_field.ty(self.tcx(), substs)
 647                         );
 648                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 649                     }
 650                 }
 651             }
 652             _ => {
 653                 // the base expression should always evaluate to a
 654                 // struct; however, when EUV is run during typeck, it
 655                 // may not. This will generate an error earlier in typeck,
 656                 // so we can just ignore it.
 657                 if !self.tcx().sess.has_errors() {
 658                     span_bug!(
 659                         with_expr.span,
 660                         "with expression doesn't evaluate to a struct");
 661                 }
 662             }
 663         }
 664
 665         // walk the with expression so that complex expressions
 666         // are properly handled.
 667         self.walk_expr(with_expr);
 668
 669         fn contains_field_named(field: &ty::FieldDef,
 670                                 fields: &[hir::Field])
 671                                 -> bool
 672         {
 673             fields.iter().any(
 674                 |f| f.name.node == field.name)
 675         }
 676     }
 677
 678     // Invoke the appropriate delegate calls for anything that gets
 679     // consumed or borrowed as part of the automatic adjustment
 680     // process.
 681     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 682         //NOTE(@jroesch): mixed RefCell borrow causes crash
 683         let adjustments = self.mc.infcx.tables.borrow().expr_adjustments(expr).to_vec();
 684         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 685         for adjustment in adjustments {
 686             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 687             match adjustment.kind {
 688                 adjustment::Adjust::NeverToAny |
 689                 adjustment::Adjust::ReifyFnPointer |
 690                 adjustment::Adjust::UnsafeFnPointer |
 691                 adjustment::Adjust::ClosureFnPointer |
 692                 adjustment::Adjust::MutToConstPointer |
 693                 adjustment::Adjust::Unsize => {
 694                     // Creating a closure/fn-pointer or unsizing consumes
 695                     // the input and stores it into the resulting rvalue.
 696                     self.delegate_consume(expr.id, expr.span, cmt.clone());
 697                 }
 698
 699                 adjustment::Adjust::Deref(None) => {}
 700
 701                 // Autoderefs for overloaded Deref calls in fact reference
 702                 // their receiver. That is, if we have `(*x)` where `x`
 703                 // is of type `Rc<T>`, then this in fact is equivalent to
 704                 // `x.deref()`. Since `deref()` is declared with `&self`,
 705                 // this is an autoref of `x`.
 706                 adjustment::Adjust::Deref(Some(ref deref)) => {
 707                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 708                     self.delegate.borrow(expr.id, expr.span, cmt.clone(),
 709                                          deref.region, bk, AutoRef);
 710                 }
 711
 712                 adjustment::Adjust::Borrow(ref autoref) => {
 713                     self.walk_autoref(expr, cmt.clone(), autoref);
 714                 }
 715             }
 716             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 717         }
 718     }
 719
 720     /// Walks the autoref `autoref` applied to the autoderef'd
 721     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 722     /// after all relevant autoderefs have occurred.
 723     fn walk_autoref(&mut self,
 724                     expr: &hir::Expr,
 725                     cmt_base: mc::cmt<'tcx>,
 726                     autoref: &adjustment::AutoBorrow<'tcx>) {
 727         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 728                expr.id,
 729                cmt_base,
 730                autoref);
 731
 732         match *autoref {
 733             adjustment::AutoBorrow::Ref(r, m) => {
 734                 self.delegate.borrow(expr.id,
 735                                      expr.span,
 736                                      cmt_base,
 737                                      r,
 738                                      ty::BorrowKind::from_mutbl(m),
 739                                      AutoRef);
 740             }
 741
 742             adjustment::AutoBorrow::RawPtr(m) => {
 743                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 744                        expr.id,
 745                        cmt_base);
 746
 747                 // Converting from a &T to *T (or &mut T to *mut T) is
 748                 // treated as borrowing it for the enclosing temporary
 749                 // scope.
 750                 let r = self.tcx().node_scope_region(expr.id);
 751
 752                 self.delegate.borrow(expr.id,
 753                                      expr.span,
 754                                      cmt_base,
 755                                      r,
 756                                      ty::BorrowKind::from_mutbl(m),
 757                                      AutoUnsafe);
 758             }
 759         }
 760     }
 761
 762     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 763         let mut mode = Unknown;
 764         for pat in &arm.pats {
 765             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 766         }
 767         mode
 768     }
 769
 770     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 771         for pat in &arm.pats {
 772             self.walk_pat(discr_cmt.clone(), &pat, mode);
 773         }
 774
 775         if let Some(ref guard) = arm.guard {
 776             self.consume_expr(&guard);
 777         }
 778
 779         self.consume_expr(&arm.body);
 780     }
 781
 782     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 783     /// arg or let binding.  *Not* a match arm or nested pat.)
 784     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 785         let mut mode = Unknown;
 786         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 787         let mode = mode.match_mode();
 788         self.walk_pat(cmt_discr, pat, mode);
 789     }
 790
 791     /// Identifies any bindings within `pat` and accumulates within
 792     /// `mode` whether the overall pattern/match structure is a move,
 793     /// copy, or borrow.
 794     fn determine_pat_move_mode(&mut self,
 795                                cmt_discr: mc::cmt<'tcx>,
 796                                pat: &hir::Pat,
 797                                mode: &mut TrackMatchMode) {
 798         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 799                pat);
 800         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 801             match pat.node {
 802                 PatKind::Binding(hir::BindByRef(..), ..) =>
 803                     mode.lub(BorrowingMatch),
 804                 PatKind::Binding(hir::BindByValue(..), ..) => {
 805                     match copy_or_move(self.mc.infcx, self.param_env, &cmt_pat, PatBindingMove) {
 806                         Copy => mode.lub(CopyingMatch),
 807                         Move(..) => mode.lub(MovingMatch),
 808                     }
 809                 }
 810                 _ => {}
 811             }
 812         }));
 813     }
 814
 815     /// The core driver for walking a pattern; `match_mode` must be
 816     /// established up front, e.g. via `determine_pat_move_mode` (see
 817     /// also `walk_irrefutable_pat` for patterns that stand alone).
 818     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 819         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 820
 821         let tcx = self.tcx();
 822         let infcx = self.mc.infcx;
 823         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 824         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 825             if let PatKind::Binding(bmode, def_id, ..) = pat.node {
 826                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 827
 828                 // pat_ty: the type of the binding being produced.
 829                 let pat_ty = return_if_err!(infcx.node_ty(pat.id));
 830
 831                 // Each match binding is effectively an assignment to the
 832                 // binding being produced.
 833                 let def = Def::Local(def_id);
 834                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 835                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 836                 }
 837
 838                 // It is also a borrow or copy/move of the value being matched.
 839                 match bmode {
 840                     hir::BindByRef(m) => {
 841                         if let ty::TyRef(r, _) = pat_ty.sty {
 842                             let bk = ty::BorrowKind::from_mutbl(m);
 843                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 844                         }
 845                     }
 846                     hir::BindByValue(..) => {
 847                         let mode = copy_or_move(infcx, param_env, &cmt_pat, PatBindingMove);
 848                         debug!("walk_pat binding consuming pat");
 849                         delegate.consume_pat(pat, cmt_pat, mode);
 850                     }
 851                 }
 852             }
 853         }));
 854
 855         // Do a second pass over the pattern, calling `matched_pat` on
 856         // the interior nodes (enum variants and structs), as opposed
 857         // to the above loop's visit of than the bindings that form
 858         // the leaves of the pattern tree structure.
 859         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
 860             let qpath = match pat.node {
 861                 PatKind::Path(ref qpath) |
 862                 PatKind::TupleStruct(ref qpath, ..) |
 863                 PatKind::Struct(ref qpath, ..) => qpath,
 864                 _ => return
 865             };
 866             let def = infcx.tables.borrow().qpath_def(qpath, pat.id);
 867             match def {
 868                 Def::Variant(variant_did) |
 869                 Def::VariantCtor(variant_did, ..) => {
 870                     let enum_did = tcx.parent_def_id(variant_did).unwrap();
 871                     let downcast_cmt = if tcx.adt_def(enum_did).is_univariant() {
 872                         cmt_pat
 873                     } else {
 874                         let cmt_pat_ty = cmt_pat.ty;
 875                         mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
 876                     };
 877
 878                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 879                     delegate.matched_pat(pat, downcast_cmt, match_mode);
 880                 }
 881                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 882                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 883                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 884                     delegate.matched_pat(pat, cmt_pat, match_mode);
 885                 }
 886                 _ => {}
 887             }
 888         }));
 889     }
 890
 891     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 892         debug!("walk_captures({:?})", closure_expr);
 893
 894         self.tcx().with_freevars(closure_expr.id, |freevars| {
 895             for freevar in freevars {
 896                 let def_id = freevar.def.def_id();
 897                 let id_var = self.tcx().hir.as_local_node_id(def_id).unwrap();
 898                 let upvar_id = ty::UpvarId { var_id: id_var,
 899                                              closure_expr_id: closure_expr.id };
 900                 let upvar_capture = self.mc.infcx.upvar_capture(upvar_id).unwrap();
 901                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 902                                                                    fn_decl_span,
 903                                                                    freevar.def));
 904                 match upvar_capture {
 905                     ty::UpvarCapture::ByValue => {
 906                         let mode = copy_or_move(self.mc.infcx,
 907                                                 self.param_env,
 908                                                 &cmt_var,
 909                                                 CaptureMove);
 910                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 911                     }
 912                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 913                         self.delegate.borrow(closure_expr.id,
 914                                              fn_decl_span,
 915                                              cmt_var,
 916                                              upvar_borrow.region,
 917                                              upvar_borrow.kind,
 918                                              ClosureCapture(freevar.span));
 919                     }
 920                 }
 921             }
 922         });
 923     }
 924
 925     fn cat_captured_var(&mut self,
 926                         closure_id: ast::NodeId,
 927                         closure_span: Span,
 928                         upvar_def: Def)
 929                         -> mc::McResult<mc::cmt<'tcx>> {
 930         // Create the cmt for the variable being borrowed, from the
 931         // caller's perspective
 932         let var_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
 933         let var_ty = self.mc.infcx.node_ty(var_id)?;
 934         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 935     }
 936 }
 937
 938 fn copy_or_move<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 939                                 param_env: ty::ParamEnv<'tcx>,
 940                                 cmt: &mc::cmt<'tcx>,
 941                                 move_reason: MoveReason)
 942                                 -> ConsumeMode
 943 {
 944     if infcx.type_moves_by_default(param_env, cmt.ty, cmt.span) {
 945         Move(move_reason)
 946     } else {
 947         Copy
 948     }
 949 }