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;
  27 use ty::{self, TyCtxt, adjustment};
  28
  29 use hir::{self, PatKind};
  30 use rustc_data_structures::sync::Lrc;
  31 use syntax::ast;
  32 use syntax::ptr::P;
  33 use syntax_pos::Span;
  34 use util::nodemap::ItemLocalSet;
  35
  36 ///////////////////////////////////////////////////////////////////////////
  37 // The Delegate trait
  38
  39 /// This trait defines the callbacks you can expect to receive when
  40 /// employing the ExprUseVisitor.
  41 pub trait Delegate<'tcx> {
  42     // The value found at `cmt` is either copied or moved, depending
  43     // on mode.
  44     fn consume(&mut self,
  45                consume_id: ast::NodeId,
  46                consume_span: Span,
  47                cmt: mc::cmt<'tcx>,
  48                mode: ConsumeMode);
  49
  50     // The value found at `cmt` has been determined to match the
  51     // pattern binding `matched_pat`, and its subparts are being
  52     // copied or moved depending on `mode`.  Note that `matched_pat`
  53     // is called on all variant/structs in the pattern (i.e., the
  54     // interior nodes of the pattern's tree structure) while
  55     // consume_pat is called on the binding identifiers in the pattern
  56     // (which are leaves of the pattern's tree structure).
  57     //
  58     // Note that variants/structs and identifiers are disjoint; thus
  59     // `matched_pat` and `consume_pat` are never both called on the
  60     // same input pattern structure (though of `consume_pat` can be
  61     // called on a subpart of an input passed to `matched_pat).
  62     fn matched_pat(&mut self,
  63                    matched_pat: &hir::Pat,
  64                    cmt: mc::cmt<'tcx>,
  65                    mode: MatchMode);
  66
  67     // The value found at `cmt` is either copied or moved via the
  68     // pattern binding `consume_pat`, depending on mode.
  69     fn consume_pat(&mut self,
  70                    consume_pat: &hir::Pat,
  71                    cmt: mc::cmt<'tcx>,
  72                    mode: ConsumeMode);
  73
  74     // The value found at `borrow` is being borrowed at the point
  75     // `borrow_id` for the region `loan_region` with kind `bk`.
  76     fn borrow(&mut self,
  77               borrow_id: ast::NodeId,
  78               borrow_span: Span,
  79               cmt: mc::cmt<'tcx>,
  80               loan_region: ty::Region<'tcx>,
  81               bk: ty::BorrowKind,
  82               loan_cause: LoanCause);
  83
  84     // The local variable `id` is declared but not initialized.
  85     fn decl_without_init(&mut self,
  86                          id: ast::NodeId,
  87                          span: Span);
  88
  89     // The path at `cmt` is being assigned to.
  90     fn mutate(&mut self,
  91               assignment_id: ast::NodeId,
  92               assignment_span: Span,
  93               assignee_cmt: mc::cmt<'tcx>,
  94               mode: MutateMode);
  95 }
  96
  97 #[derive(Copy, Clone, PartialEq, Debug)]
  98 pub enum LoanCause {
  99     ClosureCapture(Span),
 100     AddrOf,
 101     AutoRef,
 102     AutoUnsafe,
 103     RefBinding,
 104     OverloadedOperator,
 105     ClosureInvocation,
 106     ForLoop,
 107     MatchDiscriminant
 108 }
 109
 110 #[derive(Copy, Clone, PartialEq, Debug)]
 111 pub enum ConsumeMode {
 112     Copy,                // reference to x where x has a type that copies
 113     Move(MoveReason),    // reference to x where x has a type that moves
 114 }
 115
 116 #[derive(Copy, Clone, PartialEq, Debug)]
 117 pub enum MoveReason {
 118     DirectRefMove,
 119     PatBindingMove,
 120     CaptureMove,
 121 }
 122
 123 #[derive(Copy, Clone, PartialEq, Debug)]
 124 pub enum MatchMode {
 125     NonBindingMatch,
 126     BorrowingMatch,
 127     CopyingMatch,
 128     MovingMatch,
 129 }
 130
 131 #[derive(Copy, Clone, PartialEq, Debug)]
 132 enum TrackMatchMode {
 133     Unknown,
 134     Definite(MatchMode),
 135     Conflicting,
 136 }
 137
 138 impl TrackMatchMode {
 139     // Builds up the whole match mode for a pattern from its constituent
 140     // parts.  The lattice looks like this:
 141     //
 142     //          Conflicting
 143     //            /     \
 144     //           /       \
 145     //      Borrowing   Moving
 146     //           \       /
 147     //            \     /
 148     //            Copying
 149     //               |
 150     //          NonBinding
 151     //               |
 152     //            Unknown
 153     //
 154     // examples:
 155     //
 156     // * `(_, some_int)` pattern is Copying, since
 157     //   NonBinding + Copying => Copying
 158     //
 159     // * `(some_int, some_box)` pattern is Moving, since
 160     //   Copying + Moving => Moving
 161     //
 162     // * `(ref x, some_box)` pattern is Conflicting, since
 163     //   Borrowing + Moving => Conflicting
 164     //
 165     // Note that the `Unknown` and `Conflicting` states are
 166     // represented separately from the other more interesting
 167     // `Definite` states, which simplifies logic here somewhat.
 168     fn lub(&mut self, mode: MatchMode) {
 169         *self = match (*self, mode) {
 170             // Note that clause order below is very significant.
 171             (Unknown, new) => Definite(new),
 172             (Definite(old), new) if old == new => Definite(old),
 173
 174             (Definite(old), NonBindingMatch) => Definite(old),
 175             (Definite(NonBindingMatch), new) => Definite(new),
 176
 177             (Definite(old), CopyingMatch) => Definite(old),
 178             (Definite(CopyingMatch), new) => Definite(new),
 179
 180             (Definite(_), _) => Conflicting,
 181             (Conflicting, _) => *self,
 182         };
 183     }
 184
 185     fn match_mode(&self) -> MatchMode {
 186         match *self {
 187             Unknown => NonBindingMatch,
 188             Definite(mode) => mode,
 189             Conflicting => {
 190                 // Conservatively return MovingMatch to let the
 191                 // compiler continue to make progress.
 192                 MovingMatch
 193             }
 194         }
 195     }
 196 }
 197
 198 #[derive(Copy, Clone, PartialEq, Debug)]
 199 pub enum MutateMode {
 200     Init,
 201     JustWrite,    // x = y
 202     WriteAndRead, // x += y
 203 }
 204
 205 #[derive(Copy, Clone)]
 206 enum OverloadedCallType {
 207     FnOverloadedCall,
 208     FnMutOverloadedCall,
 209     FnOnceOverloadedCall,
 210 }
 211
 212 impl OverloadedCallType {
 213     fn from_trait_id(tcx: TyCtxt, trait_id: DefId) -> OverloadedCallType {
 214         for &(maybe_function_trait, overloaded_call_type) in &[
 215             (tcx.lang_items().fn_once_trait(), FnOnceOverloadedCall),
 216             (tcx.lang_items().fn_mut_trait(), FnMutOverloadedCall),
 217             (tcx.lang_items().fn_trait(), FnOverloadedCall)
 218         ] {
 219             match maybe_function_trait {
 220                 Some(function_trait) if function_trait == trait_id => {
 221                     return overloaded_call_type
 222                 }
 223                 _ => continue,
 224             }
 225         }
 226
 227         bug!("overloaded call didn't map to known function trait")
 228     }
 229
 230     fn from_method_id(tcx: TyCtxt, method_id: DefId) -> OverloadedCallType {
 231         let method = tcx.associated_item(method_id);
 232         OverloadedCallType::from_trait_id(tcx, method.container.id())
 233     }
 234 }
 235
 236 ///////////////////////////////////////////////////////////////////////////
 237 // The ExprUseVisitor type
 238 //
 239 // This is the code that actually walks the tree.
 240 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 241     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 242     delegate: &'a mut Delegate<'tcx>,
 243     param_env: ty::ParamEnv<'tcx>,
 244 }
 245
 246 // If the MC results in an error, it's because the type check
 247 // failed (or will fail, when the error is uncovered and reported
 248 // during writeback). In this case, we just ignore this part of the
 249 // code.
 250 //
 251 // Note that this macro appears similar to try!(), but, unlike try!(),
 252 // it does not propagate the error.
 253 macro_rules! return_if_err {
 254     ($inp: expr) => (
 255         match $inp {
 256             Ok(v) => v,
 257             Err(()) => {
 258                 debug!("mc reported err");
 259                 return
 260             }
 261         }
 262     )
 263 }
 264
 265 impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
 266     /// Creates the ExprUseVisitor, configuring it with the various options provided:
 267     ///
 268     /// - `delegate` -- who receives the callbacks
 269     /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
 270     /// - `region_scope_tree` --- region scope tree for the code being analyzed
 271     /// - `tables` --- typeck results for the code being analyzed
 272     /// - `rvalue_promotable_map` --- if you care about rvalue promotion, then provide
 273     ///   the map here (it can be computed with `tcx.rvalue_promotable_map(def_id)`).
 274     ///   `None` means that rvalues will be given more conservative lifetimes.
 275     ///
 276     /// See also `with_infer`, which is used *during* typeck.
 277     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 278                tcx: TyCtxt<'a, 'tcx, 'tcx>,
 279                param_env: ty::ParamEnv<'tcx>,
 280                region_scope_tree: &'a region::ScopeTree,
 281                tables: &'a ty::TypeckTables<'tcx>,
 282                rvalue_promotable_map: Option<Lrc<ItemLocalSet>>)
 283                -> Self
 284     {
 285         ExprUseVisitor {
 286             mc: mc::MemCategorizationContext::new(tcx,
 287                                                   region_scope_tree,
 288                                                   tables,
 289                                                   rvalue_promotable_map),
 290             delegate,
 291             param_env,
 292         }
 293     }
 294 }
 295
 296 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 297     pub fn with_infer(delegate: &'a mut (Delegate<'tcx>+'a),
 298                       infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 299                       param_env: ty::ParamEnv<'tcx>,
 300                       region_scope_tree: &'a region::ScopeTree,
 301                       tables: &'a ty::TypeckTables<'tcx>)
 302                       -> Self
 303     {
 304         ExprUseVisitor {
 305             mc: mc::MemCategorizationContext::with_infer(infcx, region_scope_tree, tables),
 306             delegate,
 307             param_env,
 308         }
 309     }
 310
 311     pub fn consume_body(&mut self, body: &hir::Body) {
 312         debug!("consume_body(body={:?})", body);
 313
 314         for arg in &body.arguments {
 315             let arg_ty = return_if_err!(self.mc.node_ty(arg.pat.hir_id));
 316
 317             let fn_body_scope_r =
 318                 self.tcx().mk_region(ty::ReScope(region::Scope::Node(body.value.hir_id.local_id)));
 319             let arg_cmt = self.mc.cat_rvalue(
 320                 arg.id,
 321                 arg.pat.span,
 322                 fn_body_scope_r, // Args live only as long as the fn body.
 323                 arg_ty);
 324
 325             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 326         }
 327
 328         self.consume_expr(&body.value);
 329     }
 330
 331     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 332         self.mc.tcx
 333     }
 334
 335     fn delegate_consume(&mut self,
 336                         consume_id: ast::NodeId,
 337                         consume_span: Span,
 338                         cmt: mc::cmt<'tcx>) {
 339         debug!("delegate_consume(consume_id={}, cmt={:?})",
 340                consume_id, cmt);
 341
 342         let mode = copy_or_move(&self.mc, self.param_env, &cmt, DirectRefMove);
 343         self.delegate.consume(consume_id, consume_span, cmt, mode);
 344     }
 345
 346     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 347         for expr in exprs {
 348             self.consume_expr(&expr);
 349         }
 350     }
 351
 352     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 353         debug!("consume_expr(expr={:?})", expr);
 354
 355         let cmt = return_if_err!(self.mc.cat_expr(expr));
 356         self.delegate_consume(expr.id, expr.span, cmt);
 357         self.walk_expr(expr);
 358     }
 359
 360     fn mutate_expr(&mut self,
 361                    assignment_expr: &hir::Expr,
 362                    expr: &hir::Expr,
 363                    mode: MutateMode) {
 364         let cmt = return_if_err!(self.mc.cat_expr(expr));
 365         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 366         self.walk_expr(expr);
 367     }
 368
 369     fn borrow_expr(&mut self,
 370                    expr: &hir::Expr,
 371                    r: ty::Region<'tcx>,
 372                    bk: ty::BorrowKind,
 373                    cause: LoanCause) {
 374         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 375                expr, r, bk);
 376
 377         let cmt = return_if_err!(self.mc.cat_expr(expr));
 378         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 379
 380         self.walk_expr(expr)
 381     }
 382
 383     fn select_from_expr(&mut self, expr: &hir::Expr) {
 384         self.walk_expr(expr)
 385     }
 386
 387     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 388         debug!("walk_expr(expr={:?})", expr);
 389
 390         self.walk_adjustment(expr);
 391
 392         match expr.node {
 393             hir::ExprPath(_) => { }
 394
 395             hir::ExprType(ref subexpr, _) => {
 396                 self.walk_expr(&subexpr)
 397             }
 398
 399             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 400                 self.select_from_expr(&base);
 401             }
 402
 403             hir::ExprField(ref base, _) => {         // base.f
 404                 self.select_from_expr(&base);
 405             }
 406
 407             hir::ExprTupField(ref base, _) => {         // base.<n>
 408                 self.select_from_expr(&base);
 409             }
 410
 411             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 412                 self.select_from_expr(&lhs);
 413                 self.consume_expr(&rhs);
 414             }
 415
 416             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 417                 self.walk_callee(expr, &callee);
 418                 self.consume_exprs(args);
 419             }
 420
 421             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 422                 self.consume_exprs(args);
 423             }
 424
 425             hir::ExprStruct(_, ref fields, ref opt_with) => {
 426                 self.walk_struct_expr(fields, opt_with);
 427             }
 428
 429             hir::ExprTup(ref exprs) => {
 430                 self.consume_exprs(exprs);
 431             }
 432
 433             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 434                 self.consume_expr(&cond_expr);
 435                 self.walk_expr(&then_expr);
 436                 if let Some(ref else_expr) = *opt_else_expr {
 437                     self.consume_expr(&else_expr);
 438                 }
 439             }
 440
 441             hir::ExprMatch(ref discr, ref arms, _) => {
 442                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 443                 let r = self.tcx().types.re_empty;
 444                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 445
 446                 // treatment of the discriminant is handled while walking the arms.
 447                 for arm in arms {
 448                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 449                     let mode = mode.match_mode();
 450                     self.walk_arm(discr_cmt.clone(), arm, mode);
 451                 }
 452             }
 453
 454             hir::ExprArray(ref exprs) => {
 455                 self.consume_exprs(exprs);
 456             }
 457
 458             hir::ExprAddrOf(m, ref base) => {   // &base
 459                 // make sure that the thing we are pointing out stays valid
 460                 // for the lifetime `scope_r` of the resulting ptr:
 461                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 462                 if let ty::TyRef(r, _) = expr_ty.sty {
 463                     let bk = ty::BorrowKind::from_mutbl(m);
 464                     self.borrow_expr(&base, r, bk, AddrOf);
 465                 }
 466             }
 467
 468             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 469                 for (o, output) in ia.outputs.iter().zip(outputs) {
 470                     if o.is_indirect {
 471                         self.consume_expr(output);
 472                     } else {
 473                         self.mutate_expr(expr, output,
 474                                          if o.is_rw {
 475                                              MutateMode::WriteAndRead
 476                                          } else {
 477                                              MutateMode::JustWrite
 478                                          });
 479                     }
 480                 }
 481                 self.consume_exprs(inputs);
 482             }
 483
 484             hir::ExprAgain(..) |
 485             hir::ExprLit(..) => {}
 486
 487             hir::ExprLoop(ref blk, _, _) => {
 488                 self.walk_block(&blk);
 489             }
 490
 491             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 492                 self.consume_expr(&cond_expr);
 493                 self.walk_block(&blk);
 494             }
 495
 496             hir::ExprUnary(_, ref lhs) => {
 497                 self.consume_expr(&lhs);
 498             }
 499
 500             hir::ExprBinary(_, ref lhs, ref rhs) => {
 501                 self.consume_expr(&lhs);
 502                 self.consume_expr(&rhs);
 503             }
 504
 505             hir::ExprBlock(ref blk) => {
 506                 self.walk_block(&blk);
 507             }
 508
 509             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 510                 if let Some(ref expr) = *opt_expr {
 511                     self.consume_expr(&expr);
 512                 }
 513             }
 514
 515             hir::ExprAssign(ref lhs, ref rhs) => {
 516                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 517                 self.consume_expr(&rhs);
 518             }
 519
 520             hir::ExprCast(ref base, _) => {
 521                 self.consume_expr(&base);
 522             }
 523
 524             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 525                 if self.mc.tables.is_method_call(expr) {
 526                     self.consume_expr(lhs);
 527                 } else {
 528                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 529                 }
 530                 self.consume_expr(&rhs);
 531             }
 532
 533             hir::ExprRepeat(ref base, _) => {
 534                 self.consume_expr(&base);
 535             }
 536
 537             hir::ExprClosure(.., fn_decl_span, _) => {
 538                 self.walk_captures(expr, fn_decl_span)
 539             }
 540
 541             hir::ExprBox(ref base) => {
 542                 self.consume_expr(&base);
 543             }
 544
 545             hir::ExprYield(ref value) => {
 546                 self.consume_expr(&value);
 547             }
 548         }
 549     }
 550
 551     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 552         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 553         debug!("walk_callee: callee={:?} callee_ty={:?}",
 554                callee, callee_ty);
 555         match callee_ty.sty {
 556             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 557                 self.consume_expr(callee);
 558             }
 559             ty::TyError => { }
 560             _ => {
 561                 if let Some(def) = self.mc.tables.type_dependent_defs().get(call.hir_id) {
 562                     let def_id = def.def_id();
 563                     let call_scope = region::Scope::Node(call.hir_id.local_id);
 564                     match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 565                         FnMutOverloadedCall => {
 566                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 567                             self.borrow_expr(callee,
 568                                             call_scope_r,
 569                                             ty::MutBorrow,
 570                                             ClosureInvocation);
 571                         }
 572                         FnOverloadedCall => {
 573                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 574                             self.borrow_expr(callee,
 575                                             call_scope_r,
 576                                             ty::ImmBorrow,
 577                                             ClosureInvocation);
 578                         }
 579                         FnOnceOverloadedCall => self.consume_expr(callee),
 580                     }
 581                 } else {
 582                     self.tcx().sess.delay_span_bug(call.span,
 583                                                    "no type-dependent def for overloaded call");
 584                 }
 585             }
 586         }
 587     }
 588
 589     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 590         match stmt.node {
 591             hir::StmtDecl(ref decl, _) => {
 592                 match decl.node {
 593                     hir::DeclLocal(ref local) => {
 594                         self.walk_local(&local);
 595                     }
 596
 597                     hir::DeclItem(_) => {
 598                         // we don't visit nested items in this visitor,
 599                         // only the fn body we were given.
 600                     }
 601                 }
 602             }
 603
 604             hir::StmtExpr(ref expr, _) |
 605             hir::StmtSemi(ref expr, _) => {
 606                 self.consume_expr(&expr);
 607             }
 608         }
 609     }
 610
 611     fn walk_local(&mut self, local: &hir::Local) {
 612         match local.init {
 613             None => {
 614                 let delegate = &mut self.delegate;
 615                 local.pat.each_binding(|_, id, span, _| {
 616                     delegate.decl_without_init(id, span);
 617                 })
 618             }
 619
 620             Some(ref expr) => {
 621                 // Variable declarations with
 622                 // initializers are considered
 623                 // "assigns", which is handled by
 624                 // `walk_pat`:
 625                 self.walk_expr(&expr);
 626                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 627                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 628             }
 629         }
 630     }
 631
 632     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 633     /// depending on its type.
 634     fn walk_block(&mut self, blk: &hir::Block) {
 635         debug!("walk_block(blk.id={})", blk.id);
 636
 637         for stmt in &blk.stmts {
 638             self.walk_stmt(stmt);
 639         }
 640
 641         if let Some(ref tail_expr) = blk.expr {
 642             self.consume_expr(&tail_expr);
 643         }
 644     }
 645
 646     fn walk_struct_expr(&mut self,
 647                         fields: &[hir::Field],
 648                         opt_with: &Option<P<hir::Expr>>) {
 649         // Consume the expressions supplying values for each field.
 650         for field in fields {
 651             self.consume_expr(&field.expr);
 652         }
 653
 654         let with_expr = match *opt_with {
 655             Some(ref w) => &**w,
 656             None => { return; }
 657         };
 658
 659         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 660
 661         // Select just those fields of the `with`
 662         // expression that will actually be used
 663         match with_cmt.ty.sty {
 664             ty::TyAdt(adt, substs) if adt.is_struct() => {
 665                 // Consume those fields of the with expression that are needed.
 666                 for with_field in &adt.non_enum_variant().fields {
 667                     if !contains_field_named(with_field, fields) {
 668                         let cmt_field = self.mc.cat_field(
 669                             &*with_expr,
 670                             with_cmt.clone(),
 671                             with_field.name,
 672                             with_field.ty(self.tcx(), substs)
 673                         );
 674                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 675                     }
 676                 }
 677             }
 678             _ => {
 679                 // the base expression should always evaluate to a
 680                 // struct; however, when EUV is run during typeck, it
 681                 // may not. This will generate an error earlier in typeck,
 682                 // so we can just ignore it.
 683                 if !self.tcx().sess.has_errors() {
 684                     span_bug!(
 685                         with_expr.span,
 686                         "with expression doesn't evaluate to a struct");
 687                 }
 688             }
 689         }
 690
 691         // walk the with expression so that complex expressions
 692         // are properly handled.
 693         self.walk_expr(with_expr);
 694
 695         fn contains_field_named(field: &ty::FieldDef,
 696                                 fields: &[hir::Field])
 697                                 -> bool
 698         {
 699             fields.iter().any(
 700                 |f| f.name.node == field.name)
 701         }
 702     }
 703
 704     // Invoke the appropriate delegate calls for anything that gets
 705     // consumed or borrowed as part of the automatic adjustment
 706     // process.
 707     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 708         let adjustments = self.mc.tables.expr_adjustments(expr);
 709         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 710         for adjustment in adjustments {
 711             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 712             match adjustment.kind {
 713                 adjustment::Adjust::NeverToAny |
 714                 adjustment::Adjust::ReifyFnPointer |
 715                 adjustment::Adjust::UnsafeFnPointer |
 716                 adjustment::Adjust::ClosureFnPointer |
 717                 adjustment::Adjust::MutToConstPointer |
 718                 adjustment::Adjust::Unsize => {
 719                     // Creating a closure/fn-pointer or unsizing consumes
 720                     // the input and stores it into the resulting rvalue.
 721                     self.delegate_consume(expr.id, expr.span, cmt.clone());
 722                 }
 723
 724                 adjustment::Adjust::Deref(None) => {}
 725
 726                 // Autoderefs for overloaded Deref calls in fact reference
 727                 // their receiver. That is, if we have `(*x)` where `x`
 728                 // is of type `Rc<T>`, then this in fact is equivalent to
 729                 // `x.deref()`. Since `deref()` is declared with `&self`,
 730                 // this is an autoref of `x`.
 731                 adjustment::Adjust::Deref(Some(ref deref)) => {
 732                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 733                     self.delegate.borrow(expr.id, expr.span, cmt.clone(),
 734                                          deref.region, bk, AutoRef);
 735                 }
 736
 737                 adjustment::Adjust::Borrow(ref autoref) => {
 738                     self.walk_autoref(expr, cmt.clone(), autoref);
 739                 }
 740             }
 741             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 742         }
 743     }
 744
 745     /// Walks the autoref `autoref` applied to the autoderef'd
 746     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 747     /// after all relevant autoderefs have occurred.
 748     fn walk_autoref(&mut self,
 749                     expr: &hir::Expr,
 750                     cmt_base: mc::cmt<'tcx>,
 751                     autoref: &adjustment::AutoBorrow<'tcx>) {
 752         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 753                expr.id,
 754                cmt_base,
 755                autoref);
 756
 757         match *autoref {
 758             adjustment::AutoBorrow::Ref(r, m) => {
 759                 self.delegate.borrow(expr.id,
 760                                      expr.span,
 761                                      cmt_base,
 762                                      r,
 763                                      ty::BorrowKind::from_mutbl(m.into()),
 764                                      AutoRef);
 765             }
 766
 767             adjustment::AutoBorrow::RawPtr(m) => {
 768                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 769                        expr.id,
 770                        cmt_base);
 771
 772                 // Converting from a &T to *T (or &mut T to *mut T) is
 773                 // treated as borrowing it for the enclosing temporary
 774                 // scope.
 775                 let r = self.tcx().mk_region(ty::ReScope(
 776                     region::Scope::Node(expr.hir_id.local_id)));
 777
 778                 self.delegate.borrow(expr.id,
 779                                      expr.span,
 780                                      cmt_base,
 781                                      r,
 782                                      ty::BorrowKind::from_mutbl(m),
 783                                      AutoUnsafe);
 784             }
 785         }
 786     }
 787
 788     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 789         let mut mode = Unknown;
 790         for pat in &arm.pats {
 791             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 792         }
 793         mode
 794     }
 795
 796     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 797         for pat in &arm.pats {
 798             self.walk_pat(discr_cmt.clone(), &pat, mode);
 799         }
 800
 801         if let Some(ref guard) = arm.guard {
 802             self.consume_expr(&guard);
 803         }
 804
 805         self.consume_expr(&arm.body);
 806     }
 807
 808     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 809     /// arg or let binding.  *Not* a match arm or nested pat.)
 810     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 811         let mut mode = Unknown;
 812         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 813         let mode = mode.match_mode();
 814         self.walk_pat(cmt_discr, pat, mode);
 815     }
 816
 817     /// Identifies any bindings within `pat` and accumulates within
 818     /// `mode` whether the overall pattern/match structure is a move,
 819     /// copy, or borrow.
 820     fn determine_pat_move_mode(&mut self,
 821                                cmt_discr: mc::cmt<'tcx>,
 822                                pat: &hir::Pat,
 823                                mode: &mut TrackMatchMode) {
 824         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 825                pat);
 826         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 827             if let PatKind::Binding(..) = pat.node {
 828                 let bm = *self.mc.tables.pat_binding_modes().get(pat.hir_id)
 829                                                           .expect("missing binding mode");
 830                 match bm {
 831                     ty::BindByReference(..) =>
 832                         mode.lub(BorrowingMatch),
 833                     ty::BindByValue(..) => {
 834                         match copy_or_move(&self.mc, self.param_env, &cmt_pat, PatBindingMove) {
 835                             Copy => mode.lub(CopyingMatch),
 836                             Move(..) => mode.lub(MovingMatch),
 837                         }
 838                     }
 839                 }
 840             }
 841         }));
 842     }
 843
 844     /// The core driver for walking a pattern; `match_mode` must be
 845     /// established up front, e.g. via `determine_pat_move_mode` (see
 846     /// also `walk_irrefutable_pat` for patterns that stand alone).
 847     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 848         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 849
 850         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 851         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 852             if let PatKind::Binding(_, canonical_id, ..) = pat.node {
 853                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 854                 let bm = *mc.tables.pat_binding_modes().get(pat.hir_id)
 855                                                      .expect("missing binding mode");
 856
 857                 // pat_ty: the type of the binding being produced.
 858                 let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
 859
 860                 // Each match binding is effectively an assignment to the
 861                 // binding being produced.
 862                 let def = Def::Local(canonical_id);
 863                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 864                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 865                 }
 866
 867                 // It is also a borrow or copy/move of the value being matched.
 868                 match bm {
 869                     ty::BindByReference(m) => {
 870                         if let ty::TyRef(r, _) = pat_ty.sty {
 871                             let bk = ty::BorrowKind::from_mutbl(m);
 872                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 873                         }
 874                     }
 875                     ty::BindByValue(..) => {
 876                         let mode = copy_or_move(mc, param_env, &cmt_pat, PatBindingMove);
 877                         debug!("walk_pat binding consuming pat");
 878                         delegate.consume_pat(pat, cmt_pat, mode);
 879                     }
 880                 }
 881             }
 882         }));
 883
 884         // Do a second pass over the pattern, calling `matched_pat` on
 885         // the interior nodes (enum variants and structs), as opposed
 886         // to the above loop's visit of than the bindings that form
 887         // the leaves of the pattern tree structure.
 888         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 889             let qpath = match pat.node {
 890                 PatKind::Path(ref qpath) |
 891                 PatKind::TupleStruct(ref qpath, ..) |
 892                 PatKind::Struct(ref qpath, ..) => qpath,
 893                 _ => return
 894             };
 895             let def = mc.tables.qpath_def(qpath, pat.hir_id);
 896             match def {
 897                 Def::Variant(variant_did) |
 898                 Def::VariantCtor(variant_did, ..) => {
 899                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 900
 901                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 902                     delegate.matched_pat(pat, downcast_cmt, match_mode);
 903                 }
 904                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 905                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 906                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 907                     delegate.matched_pat(pat, cmt_pat, match_mode);
 908                 }
 909                 _ => {}
 910             }
 911         }));
 912     }
 913
 914     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 915         debug!("walk_captures({:?})", closure_expr);
 916
 917         self.tcx().with_freevars(closure_expr.id, |freevars| {
 918             for freevar in freevars {
 919                 let var_hir_id = self.tcx().hir.node_to_hir_id(freevar.var_id());
 920                 let closure_def_id = self.tcx().hir.local_def_id(closure_expr.id);
 921                 let upvar_id = ty::UpvarId {
 922                     var_id: var_hir_id,
 923                     closure_expr_id: closure_def_id.to_local(),
 924                 };
 925                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 926                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 927                                                                    fn_decl_span,
 928                                                                    freevar));
 929                 match upvar_capture {
 930                     ty::UpvarCapture::ByValue => {
 931                         let mode = copy_or_move(&self.mc,
 932                                                 self.param_env,
 933                                                 &cmt_var,
 934                                                 CaptureMove);
 935                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 936                     }
 937                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 938                         self.delegate.borrow(closure_expr.id,
 939                                              fn_decl_span,
 940                                              cmt_var,
 941                                              upvar_borrow.region,
 942                                              upvar_borrow.kind,
 943                                              ClosureCapture(freevar.span));
 944                     }
 945                 }
 946             }
 947         });
 948     }
 949
 950     fn cat_captured_var(&mut self,
 951                         closure_id: ast::NodeId,
 952                         closure_span: Span,
 953                         upvar: &hir::Freevar)
 954                         -> mc::McResult<mc::cmt<'tcx>> {
 955         // Create the cmt for the variable being borrowed, from the
 956         // caller's perspective
 957         let var_hir_id = self.tcx().hir.node_to_hir_id(upvar.var_id());
 958         let var_ty = self.mc.node_ty(var_hir_id)?;
 959         self.mc.cat_def(closure_id, closure_span, var_ty, upvar.def)
 960     }
 961 }
 962
 963 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 964                                 param_env: ty::ParamEnv<'tcx>,
 965                                 cmt: &mc::cmt<'tcx>,
 966                                 move_reason: MoveReason)
 967                                 -> ConsumeMode
 968 {
 969     if mc.type_moves_by_default(param_env, cmt.ty, cmt.span) {
 970         Move(move_reason)
 971     } else {
 972         Copy
 973     }
 974 }