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