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.
 239 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 240     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 241     delegate: &'a mut Delegate<'tcx>,
 242     param_env: ty::ParamEnv<'tcx>,
 243 }
 244
 245 // If the MC results in an error, it's because the type check
 246 // failed (or will fail, when the error is uncovered and reported
 247 // during writeback). In this case, we just ignore this part of the
 248 // code.
 249 //
 250 // Note that this macro appears similar to try!(), but, unlike try!(),
 251 // it does not propagate the error.
 252 macro_rules! return_if_err {
 253     ($inp: expr) => (
 254         match $inp {
 255             Ok(v) => v,
 256             Err(()) => {
 257                 debug!("mc reported err");
 258                 return
 259             }
 260         }
 261     )
 262 }
 263
 264 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 265     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 266                infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 267                param_env: ty::ParamEnv<'tcx>,
 268                region_maps: &'a RegionMaps,
 269                tables: &'a ty::TypeckTables<'tcx>)
 270                -> Self
 271     {
 272         ExprUseVisitor {
 273             mc: mc::MemCategorizationContext::new(infcx, region_maps, tables),
 274             delegate,
 275             param_env,
 276         }
 277     }
 278
 279     pub fn consume_body(&mut self, body: &hir::Body) {
 280         debug!("consume_body(body={:?})", body);
 281
 282         for arg in &body.arguments {
 283             let arg_ty = return_if_err!(self.mc.node_ty(arg.pat.id));
 284
 285             let fn_body_scope_r = self.tcx().node_scope_region(body.value.id);
 286             let arg_cmt = self.mc.cat_rvalue(
 287                 arg.id,
 288                 arg.pat.span,
 289                 fn_body_scope_r, // Args live only as long as the fn body.
 290                 arg_ty);
 291
 292             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 293         }
 294
 295         self.consume_expr(&body.value);
 296     }
 297
 298     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 299         self.mc.infcx.tcx
 300     }
 301
 302     fn delegate_consume(&mut self,
 303                         consume_id: ast::NodeId,
 304                         consume_span: Span,
 305                         cmt: mc::cmt<'tcx>) {
 306         debug!("delegate_consume(consume_id={}, cmt={:?})",
 307                consume_id, cmt);
 308
 309         let mode = copy_or_move(self.mc.infcx, self.param_env, &cmt, DirectRefMove);
 310         self.delegate.consume(consume_id, consume_span, cmt, mode);
 311     }
 312
 313     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 314         for expr in exprs {
 315             self.consume_expr(&expr);
 316         }
 317     }
 318
 319     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 320         debug!("consume_expr(expr={:?})", expr);
 321
 322         let cmt = return_if_err!(self.mc.cat_expr(expr));
 323         self.delegate_consume(expr.id, expr.span, cmt);
 324         self.walk_expr(expr);
 325     }
 326
 327     fn mutate_expr(&mut self,
 328                    assignment_expr: &hir::Expr,
 329                    expr: &hir::Expr,
 330                    mode: MutateMode) {
 331         let cmt = return_if_err!(self.mc.cat_expr(expr));
 332         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 333         self.walk_expr(expr);
 334     }
 335
 336     fn borrow_expr(&mut self,
 337                    expr: &hir::Expr,
 338                    r: ty::Region<'tcx>,
 339                    bk: ty::BorrowKind,
 340                    cause: LoanCause) {
 341         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 342                expr, r, bk);
 343
 344         let cmt = return_if_err!(self.mc.cat_expr(expr));
 345         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 346
 347         self.walk_expr(expr)
 348     }
 349
 350     fn select_from_expr(&mut self, expr: &hir::Expr) {
 351         self.walk_expr(expr)
 352     }
 353
 354     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 355         debug!("walk_expr(expr={:?})", expr);
 356
 357         self.walk_adjustment(expr);
 358
 359         match expr.node {
 360             hir::ExprPath(_) => { }
 361
 362             hir::ExprType(ref subexpr, _) => {
 363                 self.walk_expr(&subexpr)
 364             }
 365
 366             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 367                 self.select_from_expr(&base);
 368             }
 369
 370             hir::ExprField(ref base, _) => {         // base.f
 371                 self.select_from_expr(&base);
 372             }
 373
 374             hir::ExprTupField(ref base, _) => {         // base.<n>
 375                 self.select_from_expr(&base);
 376             }
 377
 378             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 379                 self.select_from_expr(&lhs);
 380                 self.consume_expr(&rhs);
 381             }
 382
 383             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 384                 self.walk_callee(expr, &callee);
 385                 self.consume_exprs(args);
 386             }
 387
 388             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 389                 self.consume_exprs(args);
 390             }
 391
 392             hir::ExprStruct(_, ref fields, ref opt_with) => {
 393                 self.walk_struct_expr(fields, opt_with);
 394             }
 395
 396             hir::ExprTup(ref exprs) => {
 397                 self.consume_exprs(exprs);
 398             }
 399
 400             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 401                 self.consume_expr(&cond_expr);
 402                 self.walk_expr(&then_expr);
 403                 if let Some(ref else_expr) = *opt_else_expr {
 404                     self.consume_expr(&else_expr);
 405                 }
 406             }
 407
 408             hir::ExprMatch(ref discr, ref arms, _) => {
 409                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 410                 let r = self.tcx().types.re_empty;
 411                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 412
 413                 // treatment of the discriminant is handled while walking the arms.
 414                 for arm in arms {
 415                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 416                     let mode = mode.match_mode();
 417                     self.walk_arm(discr_cmt.clone(), arm, mode);
 418                 }
 419             }
 420
 421             hir::ExprArray(ref exprs) => {
 422                 self.consume_exprs(exprs);
 423             }
 424
 425             hir::ExprAddrOf(m, ref base) => {   // &base
 426                 // make sure that the thing we are pointing out stays valid
 427                 // for the lifetime `scope_r` of the resulting ptr:
 428                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 429                 if let ty::TyRef(r, _) = expr_ty.sty {
 430                     let bk = ty::BorrowKind::from_mutbl(m);
 431                     self.borrow_expr(&base, r, bk, AddrOf);
 432                 }
 433             }
 434
 435             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 436                 for (o, output) in ia.outputs.iter().zip(outputs) {
 437                     if o.is_indirect {
 438                         self.consume_expr(output);
 439                     } else {
 440                         self.mutate_expr(expr, output,
 441                                          if o.is_rw {
 442                                              MutateMode::WriteAndRead
 443                                          } else {
 444                                              MutateMode::JustWrite
 445                                          });
 446                     }
 447                 }
 448                 self.consume_exprs(inputs);
 449             }
 450
 451             hir::ExprAgain(..) |
 452             hir::ExprLit(..) => {}
 453
 454             hir::ExprLoop(ref blk, _, _) => {
 455                 self.walk_block(&blk);
 456             }
 457
 458             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 459                 self.consume_expr(&cond_expr);
 460                 self.walk_block(&blk);
 461             }
 462
 463             hir::ExprUnary(_, ref lhs) => {
 464                 self.consume_expr(&lhs);
 465             }
 466
 467             hir::ExprBinary(_, ref lhs, ref rhs) => {
 468                 self.consume_expr(&lhs);
 469                 self.consume_expr(&rhs);
 470             }
 471
 472             hir::ExprBlock(ref blk) => {
 473                 self.walk_block(&blk);
 474             }
 475
 476             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 477                 if let Some(ref expr) = *opt_expr {
 478                     self.consume_expr(&expr);
 479                 }
 480             }
 481
 482             hir::ExprAssign(ref lhs, ref rhs) => {
 483                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 484                 self.consume_expr(&rhs);
 485             }
 486
 487             hir::ExprCast(ref base, _) => {
 488                 self.consume_expr(&base);
 489             }
 490
 491             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 492                 if self.mc.tables.is_method_call(expr) {
 493                     self.consume_expr(lhs);
 494                 } else {
 495                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 496                 }
 497                 self.consume_expr(&rhs);
 498             }
 499
 500             hir::ExprRepeat(ref base, _) => {
 501                 self.consume_expr(&base);
 502             }
 503
 504             hir::ExprClosure(.., fn_decl_span) => {
 505                 self.walk_captures(expr, fn_decl_span)
 506             }
 507
 508             hir::ExprBox(ref base) => {
 509                 self.consume_expr(&base);
 510             }
 511         }
 512     }
 513
 514     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 515         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 516         debug!("walk_callee: callee={:?} callee_ty={:?}",
 517                callee, callee_ty);
 518         match callee_ty.sty {
 519             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 520                 self.consume_expr(callee);
 521             }
 522             ty::TyError => { }
 523             _ => {
 524                 let def_id = self.mc.tables.type_dependent_defs[&call.id].def_id();
 525                 match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 526                     FnMutOverloadedCall => {
 527                         let call_scope_r = self.tcx().node_scope_region(call.id);
 528                         self.borrow_expr(callee,
 529                                          call_scope_r,
 530                                          ty::MutBorrow,
 531                                          ClosureInvocation);
 532                     }
 533                     FnOverloadedCall => {
 534                         let call_scope_r = self.tcx().node_scope_region(call.id);
 535                         self.borrow_expr(callee,
 536                                          call_scope_r,
 537                                          ty::ImmBorrow,
 538                                          ClosureInvocation);
 539                     }
 540                     FnOnceOverloadedCall => self.consume_expr(callee),
 541                 }
 542             }
 543         }
 544     }
 545
 546     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 547         match stmt.node {
 548             hir::StmtDecl(ref decl, _) => {
 549                 match decl.node {
 550                     hir::DeclLocal(ref local) => {
 551                         self.walk_local(&local);
 552                     }
 553
 554                     hir::DeclItem(_) => {
 555                         // we don't visit nested items in this visitor,
 556                         // only the fn body we were given.
 557                     }
 558                 }
 559             }
 560
 561             hir::StmtExpr(ref expr, _) |
 562             hir::StmtSemi(ref expr, _) => {
 563                 self.consume_expr(&expr);
 564             }
 565         }
 566     }
 567
 568     fn walk_local(&mut self, local: &hir::Local) {
 569         match local.init {
 570             None => {
 571                 let delegate = &mut self.delegate;
 572                 local.pat.each_binding(|_, id, span, _| {
 573                     delegate.decl_without_init(id, span);
 574                 })
 575             }
 576
 577             Some(ref expr) => {
 578                 // Variable declarations with
 579                 // initializers are considered
 580                 // "assigns", which is handled by
 581                 // `walk_pat`:
 582                 self.walk_expr(&expr);
 583                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 584                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 585             }
 586         }
 587     }
 588
 589     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 590     /// depending on its type.
 591     fn walk_block(&mut self, blk: &hir::Block) {
 592         debug!("walk_block(blk.id={})", blk.id);
 593
 594         for stmt in &blk.stmts {
 595             self.walk_stmt(stmt);
 596         }
 597
 598         if let Some(ref tail_expr) = blk.expr {
 599             self.consume_expr(&tail_expr);
 600         }
 601     }
 602
 603     fn walk_struct_expr(&mut self,
 604                         fields: &[hir::Field],
 605                         opt_with: &Option<P<hir::Expr>>) {
 606         // Consume the expressions supplying values for each field.
 607         for field in fields {
 608             self.consume_expr(&field.expr);
 609         }
 610
 611         let with_expr = match *opt_with {
 612             Some(ref w) => &**w,
 613             None => { return; }
 614         };
 615
 616         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 617
 618         // Select just those fields of the `with`
 619         // expression that will actually be used
 620         match with_cmt.ty.sty {
 621             ty::TyAdt(adt, substs) if adt.is_struct() => {
 622                 // Consume those fields of the with expression that are needed.
 623                 for with_field in &adt.struct_variant().fields {
 624                     if !contains_field_named(with_field, fields) {
 625                         let cmt_field = self.mc.cat_field(
 626                             &*with_expr,
 627                             with_cmt.clone(),
 628                             with_field.name,
 629                             with_field.ty(self.tcx(), substs)
 630                         );
 631                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 632                     }
 633                 }
 634             }
 635             _ => {
 636                 // the base expression should always evaluate to a
 637                 // struct; however, when EUV is run during typeck, it
 638                 // may not. This will generate an error earlier in typeck,
 639                 // so we can just ignore it.
 640                 if !self.tcx().sess.has_errors() {
 641                     span_bug!(
 642                         with_expr.span,
 643                         "with expression doesn't evaluate to a struct");
 644                 }
 645             }
 646         }
 647
 648         // walk the with expression so that complex expressions
 649         // are properly handled.
 650         self.walk_expr(with_expr);
 651
 652         fn contains_field_named(field: &ty::FieldDef,
 653                                 fields: &[hir::Field])
 654                                 -> bool
 655         {
 656             fields.iter().any(
 657                 |f| f.name.node == field.name)
 658         }
 659     }
 660
 661     // Invoke the appropriate delegate calls for anything that gets
 662     // consumed or borrowed as part of the automatic adjustment
 663     // process.
 664     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 665         let adjustments = self.mc.tables.expr_adjustments(expr);
 666         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 667         for adjustment in adjustments {
 668             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 669             match adjustment.kind {
 670                 adjustment::Adjust::NeverToAny |
 671                 adjustment::Adjust::ReifyFnPointer |
 672                 adjustment::Adjust::UnsafeFnPointer |
 673                 adjustment::Adjust::ClosureFnPointer |
 674                 adjustment::Adjust::MutToConstPointer |
 675                 adjustment::Adjust::Unsize => {
 676                     // Creating a closure/fn-pointer or unsizing consumes
 677                     // the input and stores it into the resulting rvalue.
 678                     self.delegate_consume(expr.id, expr.span, cmt.clone());
 679                 }
 680
 681                 adjustment::Adjust::Deref(None) => {}
 682
 683                 // Autoderefs for overloaded Deref calls in fact reference
 684                 // their receiver. That is, if we have `(*x)` where `x`
 685                 // is of type `Rc<T>`, then this in fact is equivalent to
 686                 // `x.deref()`. Since `deref()` is declared with `&self`,
 687                 // this is an autoref of `x`.
 688                 adjustment::Adjust::Deref(Some(ref deref)) => {
 689                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 690                     self.delegate.borrow(expr.id, expr.span, cmt.clone(),
 691                                          deref.region, bk, AutoRef);
 692                 }
 693
 694                 adjustment::Adjust::Borrow(ref autoref) => {
 695                     self.walk_autoref(expr, cmt.clone(), autoref);
 696                 }
 697             }
 698             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 699         }
 700     }
 701
 702     /// Walks the autoref `autoref` applied to the autoderef'd
 703     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 704     /// after all relevant autoderefs have occurred.
 705     fn walk_autoref(&mut self,
 706                     expr: &hir::Expr,
 707                     cmt_base: mc::cmt<'tcx>,
 708                     autoref: &adjustment::AutoBorrow<'tcx>) {
 709         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 710                expr.id,
 711                cmt_base,
 712                autoref);
 713
 714         match *autoref {
 715             adjustment::AutoBorrow::Ref(r, m) => {
 716                 self.delegate.borrow(expr.id,
 717                                      expr.span,
 718                                      cmt_base,
 719                                      r,
 720                                      ty::BorrowKind::from_mutbl(m),
 721                                      AutoRef);
 722             }
 723
 724             adjustment::AutoBorrow::RawPtr(m) => {
 725                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 726                        expr.id,
 727                        cmt_base);
 728
 729                 // Converting from a &T to *T (or &mut T to *mut T) is
 730                 // treated as borrowing it for the enclosing temporary
 731                 // scope.
 732                 let r = self.tcx().node_scope_region(expr.id);
 733
 734                 self.delegate.borrow(expr.id,
 735                                      expr.span,
 736                                      cmt_base,
 737                                      r,
 738                                      ty::BorrowKind::from_mutbl(m),
 739                                      AutoUnsafe);
 740             }
 741         }
 742     }
 743
 744     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 745         let mut mode = Unknown;
 746         for pat in &arm.pats {
 747             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 748         }
 749         mode
 750     }
 751
 752     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 753         for pat in &arm.pats {
 754             self.walk_pat(discr_cmt.clone(), &pat, mode);
 755         }
 756
 757         if let Some(ref guard) = arm.guard {
 758             self.consume_expr(&guard);
 759         }
 760
 761         self.consume_expr(&arm.body);
 762     }
 763
 764     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 765     /// arg or let binding.  *Not* a match arm or nested pat.)
 766     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 767         let mut mode = Unknown;
 768         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 769         let mode = mode.match_mode();
 770         self.walk_pat(cmt_discr, pat, mode);
 771     }
 772
 773     /// Identifies any bindings within `pat` and accumulates within
 774     /// `mode` whether the overall pattern/match structure is a move,
 775     /// copy, or borrow.
 776     fn determine_pat_move_mode(&mut self,
 777                                cmt_discr: mc::cmt<'tcx>,
 778                                pat: &hir::Pat,
 779                                mode: &mut TrackMatchMode) {
 780         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 781                pat);
 782         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 783             match pat.node {
 784                 PatKind::Binding(hir::BindByRef(..), ..) =>
 785                     mode.lub(BorrowingMatch),
 786                 PatKind::Binding(hir::BindByValue(..), ..) => {
 787                     match copy_or_move(self.mc.infcx, self.param_env, &cmt_pat, PatBindingMove) {
 788                         Copy => mode.lub(CopyingMatch),
 789                         Move(..) => mode.lub(MovingMatch),
 790                     }
 791                 }
 792                 _ => {}
 793             }
 794         }));
 795     }
 796
 797     /// The core driver for walking a pattern; `match_mode` must be
 798     /// established up front, e.g. via `determine_pat_move_mode` (see
 799     /// also `walk_irrefutable_pat` for patterns that stand alone).
 800     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 801         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 802
 803         let tcx = self.tcx();
 804         let infcx = self.mc.infcx;
 805         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 806         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 807             if let PatKind::Binding(bmode, def_id, ..) = pat.node {
 808                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 809
 810                 // pat_ty: the type of the binding being produced.
 811                 let pat_ty = return_if_err!(mc.node_ty(pat.id));
 812
 813                 // Each match binding is effectively an assignment to the
 814                 // binding being produced.
 815                 let def = Def::Local(def_id);
 816                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 817                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 818                 }
 819
 820                 // It is also a borrow or copy/move of the value being matched.
 821                 match bmode {
 822                     hir::BindByRef(m) => {
 823                         if let ty::TyRef(r, _) = pat_ty.sty {
 824                             let bk = ty::BorrowKind::from_mutbl(m);
 825                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 826                         }
 827                     }
 828                     hir::BindByValue(..) => {
 829                         let mode = copy_or_move(infcx, param_env, &cmt_pat, PatBindingMove);
 830                         debug!("walk_pat binding consuming pat");
 831                         delegate.consume_pat(pat, cmt_pat, mode);
 832                     }
 833                 }
 834             }
 835         }));
 836
 837         // Do a second pass over the pattern, calling `matched_pat` on
 838         // the interior nodes (enum variants and structs), as opposed
 839         // to the above loop's visit of than the bindings that form
 840         // the leaves of the pattern tree structure.
 841         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 842             let qpath = match pat.node {
 843                 PatKind::Path(ref qpath) |
 844                 PatKind::TupleStruct(ref qpath, ..) |
 845                 PatKind::Struct(ref qpath, ..) => qpath,
 846                 _ => return
 847             };
 848             let def = mc.tables.qpath_def(qpath, pat.id);
 849             match def {
 850                 Def::Variant(variant_did) |
 851                 Def::VariantCtor(variant_did, ..) => {
 852                     let enum_did = tcx.parent_def_id(variant_did).unwrap();
 853                     let downcast_cmt = if tcx.adt_def(enum_did).is_univariant() {
 854                         cmt_pat
 855                     } else {
 856                         let cmt_pat_ty = cmt_pat.ty;
 857                         mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
 858                     };
 859
 860                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 861                     delegate.matched_pat(pat, downcast_cmt, match_mode);
 862                 }
 863                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 864                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 865                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 866                     delegate.matched_pat(pat, cmt_pat, match_mode);
 867                 }
 868                 _ => {}
 869             }
 870         }));
 871     }
 872
 873     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 874         debug!("walk_captures({:?})", closure_expr);
 875
 876         self.tcx().with_freevars(closure_expr.id, |freevars| {
 877             for freevar in freevars {
 878                 let def_id = freevar.def.def_id();
 879                 let id_var = self.tcx().hir.as_local_node_id(def_id).unwrap();
 880                 let upvar_id = ty::UpvarId { var_id: id_var,
 881                                              closure_expr_id: closure_expr.id };
 882                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 883                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 884                                                                    fn_decl_span,
 885                                                                    freevar.def));
 886                 match upvar_capture {
 887                     ty::UpvarCapture::ByValue => {
 888                         let mode = copy_or_move(self.mc.infcx,
 889                                                 self.param_env,
 890                                                 &cmt_var,
 891                                                 CaptureMove);
 892                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 893                     }
 894                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 895                         self.delegate.borrow(closure_expr.id,
 896                                              fn_decl_span,
 897                                              cmt_var,
 898                                              upvar_borrow.region,
 899                                              upvar_borrow.kind,
 900                                              ClosureCapture(freevar.span));
 901                     }
 902                 }
 903             }
 904         });
 905     }
 906
 907     fn cat_captured_var(&mut self,
 908                         closure_id: ast::NodeId,
 909                         closure_span: Span,
 910                         upvar_def: Def)
 911                         -> mc::McResult<mc::cmt<'tcx>> {
 912         // Create the cmt for the variable being borrowed, from the
 913         // caller's perspective
 914         let var_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
 915         let var_ty = self.mc.node_ty(var_id)?;
 916         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 917     }
 918 }
 919
 920 fn copy_or_move<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 921                                 param_env: ty::ParamEnv<'tcx>,
 922                                 cmt: &mc::cmt<'tcx>,
 923                                 move_reason: MoveReason)
 924                                 -> ConsumeMode
 925 {
 926     if infcx.type_moves_by_default(param_env, cmt.ty, cmt.span) {
 927         Move(move_reason)
 928     } else {
 929         Copy
 930     }
 931 }