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
  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, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
 265     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 266                tcx: TyCtxt<'a, 'tcx, 'tcx>,
 267                param_env: ty::ParamEnv<'tcx>,
 268                region_scope_tree: &'a region::ScopeTree,
 269                tables: &'a ty::TypeckTables<'tcx>)
 270                -> Self
 271     {
 272         ExprUseVisitor {
 273             mc: mc::MemCategorizationContext::new(tcx, region_scope_tree, tables),
 274             delegate,
 275             param_env,
 276         }
 277     }
 278 }
 279
 280 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 281     pub fn with_infer(delegate: &'a mut (Delegate<'tcx>+'a),
 282                       infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 283                       param_env: ty::ParamEnv<'tcx>,
 284                       region_scope_tree: &'a region::ScopeTree,
 285                       tables: &'a ty::TypeckTables<'tcx>)
 286                       -> Self
 287     {
 288         ExprUseVisitor {
 289             mc: mc::MemCategorizationContext::with_infer(infcx, region_scope_tree, tables),
 290             delegate,
 291             param_env,
 292         }
 293     }
 294
 295     pub fn consume_body(&mut self, body: &hir::Body) {
 296         debug!("consume_body(body={:?})", body);
 297
 298         for arg in &body.arguments {
 299             let arg_ty = return_if_err!(self.mc.node_ty(arg.pat.hir_id));
 300
 301             let fn_body_scope_r =
 302                 self.tcx().mk_region(ty::ReScope(region::Scope::Node(body.value.hir_id.local_id)));
 303             let arg_cmt = self.mc.cat_rvalue(
 304                 arg.id,
 305                 arg.pat.span,
 306                 fn_body_scope_r, // Args live only as long as the fn body.
 307                 arg_ty);
 308
 309             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 310         }
 311
 312         self.consume_expr(&body.value);
 313     }
 314
 315     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 316         self.mc.tcx
 317     }
 318
 319     fn delegate_consume(&mut self,
 320                         consume_id: ast::NodeId,
 321                         consume_span: Span,
 322                         cmt: mc::cmt<'tcx>) {
 323         debug!("delegate_consume(consume_id={}, cmt={:?})",
 324                consume_id, cmt);
 325
 326         let mode = copy_or_move(&self.mc, self.param_env, &cmt, DirectRefMove);
 327         self.delegate.consume(consume_id, consume_span, cmt, mode);
 328     }
 329
 330     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 331         for expr in exprs {
 332             self.consume_expr(&expr);
 333         }
 334     }
 335
 336     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 337         debug!("consume_expr(expr={:?})", expr);
 338
 339         let cmt = return_if_err!(self.mc.cat_expr(expr));
 340         self.delegate_consume(expr.id, expr.span, cmt);
 341         self.walk_expr(expr);
 342     }
 343
 344     fn mutate_expr(&mut self,
 345                    assignment_expr: &hir::Expr,
 346                    expr: &hir::Expr,
 347                    mode: MutateMode) {
 348         let cmt = return_if_err!(self.mc.cat_expr(expr));
 349         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 350         self.walk_expr(expr);
 351     }
 352
 353     fn borrow_expr(&mut self,
 354                    expr: &hir::Expr,
 355                    r: ty::Region<'tcx>,
 356                    bk: ty::BorrowKind,
 357                    cause: LoanCause) {
 358         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 359                expr, r, bk);
 360
 361         let cmt = return_if_err!(self.mc.cat_expr(expr));
 362         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 363
 364         self.walk_expr(expr)
 365     }
 366
 367     fn select_from_expr(&mut self, expr: &hir::Expr) {
 368         self.walk_expr(expr)
 369     }
 370
 371     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 372         debug!("walk_expr(expr={:?})", expr);
 373
 374         self.walk_adjustment(expr);
 375
 376         match expr.node {
 377             hir::ExprPath(_) => { }
 378
 379             hir::ExprType(ref subexpr, _) => {
 380                 self.walk_expr(&subexpr)
 381             }
 382
 383             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 384                 self.select_from_expr(&base);
 385             }
 386
 387             hir::ExprField(ref base, _) => {         // base.f
 388                 self.select_from_expr(&base);
 389             }
 390
 391             hir::ExprTupField(ref base, _) => {         // base.<n>
 392                 self.select_from_expr(&base);
 393             }
 394
 395             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 396                 self.select_from_expr(&lhs);
 397                 self.consume_expr(&rhs);
 398             }
 399
 400             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 401                 self.walk_callee(expr, &callee);
 402                 self.consume_exprs(args);
 403             }
 404
 405             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 406                 self.consume_exprs(args);
 407             }
 408
 409             hir::ExprStruct(_, ref fields, ref opt_with) => {
 410                 self.walk_struct_expr(fields, opt_with);
 411             }
 412
 413             hir::ExprTup(ref exprs) => {
 414                 self.consume_exprs(exprs);
 415             }
 416
 417             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 418                 self.consume_expr(&cond_expr);
 419                 self.walk_expr(&then_expr);
 420                 if let Some(ref else_expr) = *opt_else_expr {
 421                     self.consume_expr(&else_expr);
 422                 }
 423             }
 424
 425             hir::ExprMatch(ref discr, ref arms, _) => {
 426                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 427                 let r = self.tcx().types.re_empty;
 428                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 429
 430                 // treatment of the discriminant is handled while walking the arms.
 431                 for arm in arms {
 432                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 433                     let mode = mode.match_mode();
 434                     self.walk_arm(discr_cmt.clone(), arm, mode);
 435                 }
 436             }
 437
 438             hir::ExprArray(ref exprs) => {
 439                 self.consume_exprs(exprs);
 440             }
 441
 442             hir::ExprAddrOf(m, ref base) => {   // &base
 443                 // make sure that the thing we are pointing out stays valid
 444                 // for the lifetime `scope_r` of the resulting ptr:
 445                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 446                 if let ty::TyRef(r, _) = expr_ty.sty {
 447                     let bk = ty::BorrowKind::from_mutbl(m);
 448                     self.borrow_expr(&base, r, bk, AddrOf);
 449                 }
 450             }
 451
 452             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 453                 for (o, output) in ia.outputs.iter().zip(outputs) {
 454                     if o.is_indirect {
 455                         self.consume_expr(output);
 456                     } else {
 457                         self.mutate_expr(expr, output,
 458                                          if o.is_rw {
 459                                              MutateMode::WriteAndRead
 460                                          } else {
 461                                              MutateMode::JustWrite
 462                                          });
 463                     }
 464                 }
 465                 self.consume_exprs(inputs);
 466             }
 467
 468             hir::ExprAgain(..) |
 469             hir::ExprLit(..) => {}
 470
 471             hir::ExprLoop(ref blk, _, _) => {
 472                 self.walk_block(&blk);
 473             }
 474
 475             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 476                 self.consume_expr(&cond_expr);
 477                 self.walk_block(&blk);
 478             }
 479
 480             hir::ExprUnary(_, ref lhs) => {
 481                 self.consume_expr(&lhs);
 482             }
 483
 484             hir::ExprBinary(_, ref lhs, ref rhs) => {
 485                 self.consume_expr(&lhs);
 486                 self.consume_expr(&rhs);
 487             }
 488
 489             hir::ExprBlock(ref blk) => {
 490                 self.walk_block(&blk);
 491             }
 492
 493             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 494                 if let Some(ref expr) = *opt_expr {
 495                     self.consume_expr(&expr);
 496                 }
 497             }
 498
 499             hir::ExprAssign(ref lhs, ref rhs) => {
 500                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 501                 self.consume_expr(&rhs);
 502             }
 503
 504             hir::ExprCast(ref base, _) => {
 505                 self.consume_expr(&base);
 506             }
 507
 508             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 509                 if self.mc.tables.is_method_call(expr) {
 510                     self.consume_expr(lhs);
 511                 } else {
 512                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 513                 }
 514                 self.consume_expr(&rhs);
 515             }
 516
 517             hir::ExprRepeat(ref base, _) => {
 518                 self.consume_expr(&base);
 519             }
 520
 521             hir::ExprClosure(.., fn_decl_span, _) => {
 522                 self.walk_captures(expr, fn_decl_span)
 523             }
 524
 525             hir::ExprBox(ref base) => {
 526                 self.consume_expr(&base);
 527             }
 528
 529             hir::ExprYield(ref value) => {
 530                 self.consume_expr(&value);
 531             }
 532         }
 533     }
 534
 535     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 536         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 537         debug!("walk_callee: callee={:?} callee_ty={:?}",
 538                callee, callee_ty);
 539         match callee_ty.sty {
 540             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 541                 self.consume_expr(callee);
 542             }
 543             ty::TyError => { }
 544             _ => {
 545                 let def_id = self.mc.tables.type_dependent_defs()[call.hir_id].def_id();
 546                 let call_scope = region::Scope::Node(call.hir_id.local_id);
 547                 match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 548                     FnMutOverloadedCall => {
 549                         let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 550                         self.borrow_expr(callee,
 551                                          call_scope_r,
 552                                          ty::MutBorrow,
 553                                          ClosureInvocation);
 554                     }
 555                     FnOverloadedCall => {
 556                         let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 557                         self.borrow_expr(callee,
 558                                          call_scope_r,
 559                                          ty::ImmBorrow,
 560                                          ClosureInvocation);
 561                     }
 562                     FnOnceOverloadedCall => self.consume_expr(callee),
 563                 }
 564             }
 565         }
 566     }
 567
 568     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 569         match stmt.node {
 570             hir::StmtDecl(ref decl, _) => {
 571                 match decl.node {
 572                     hir::DeclLocal(ref local) => {
 573                         self.walk_local(&local);
 574                     }
 575
 576                     hir::DeclItem(_) => {
 577                         // we don't visit nested items in this visitor,
 578                         // only the fn body we were given.
 579                     }
 580                 }
 581             }
 582
 583             hir::StmtExpr(ref expr, _) |
 584             hir::StmtSemi(ref expr, _) => {
 585                 self.consume_expr(&expr);
 586             }
 587         }
 588     }
 589
 590     fn walk_local(&mut self, local: &hir::Local) {
 591         match local.init {
 592             None => {
 593                 let delegate = &mut self.delegate;
 594                 local.pat.each_binding(|_, id, span, _| {
 595                     delegate.decl_without_init(id, span);
 596                 })
 597             }
 598
 599             Some(ref expr) => {
 600                 // Variable declarations with
 601                 // initializers are considered
 602                 // "assigns", which is handled by
 603                 // `walk_pat`:
 604                 self.walk_expr(&expr);
 605                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 606                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 607             }
 608         }
 609     }
 610
 611     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 612     /// depending on its type.
 613     fn walk_block(&mut self, blk: &hir::Block) {
 614         debug!("walk_block(blk.id={})", blk.id);
 615
 616         for stmt in &blk.stmts {
 617             self.walk_stmt(stmt);
 618         }
 619
 620         if let Some(ref tail_expr) = blk.expr {
 621             self.consume_expr(&tail_expr);
 622         }
 623     }
 624
 625     fn walk_struct_expr(&mut self,
 626                         fields: &[hir::Field],
 627                         opt_with: &Option<P<hir::Expr>>) {
 628         // Consume the expressions supplying values for each field.
 629         for field in fields {
 630             self.consume_expr(&field.expr);
 631         }
 632
 633         let with_expr = match *opt_with {
 634             Some(ref w) => &**w,
 635             None => { return; }
 636         };
 637
 638         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 639
 640         // Select just those fields of the `with`
 641         // expression that will actually be used
 642         match with_cmt.ty.sty {
 643             ty::TyAdt(adt, substs) if adt.is_struct() => {
 644                 // Consume those fields of the with expression that are needed.
 645                 for with_field in &adt.struct_variant().fields {
 646                     if !contains_field_named(with_field, fields) {
 647                         let cmt_field = self.mc.cat_field(
 648                             &*with_expr,
 649                             with_cmt.clone(),
 650                             with_field.name,
 651                             with_field.ty(self.tcx(), substs)
 652                         );
 653                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 654                     }
 655                 }
 656             }
 657             _ => {
 658                 // the base expression should always evaluate to a
 659                 // struct; however, when EUV is run during typeck, it
 660                 // may not. This will generate an error earlier in typeck,
 661                 // so we can just ignore it.
 662                 if !self.tcx().sess.has_errors() {
 663                     span_bug!(
 664                         with_expr.span,
 665                         "with expression doesn't evaluate to a struct");
 666                 }
 667             }
 668         }
 669
 670         // walk the with expression so that complex expressions
 671         // are properly handled.
 672         self.walk_expr(with_expr);
 673
 674         fn contains_field_named(field: &ty::FieldDef,
 675                                 fields: &[hir::Field])
 676                                 -> bool
 677         {
 678             fields.iter().any(
 679                 |f| f.name.node == field.name)
 680         }
 681     }
 682
 683     // Invoke the appropriate delegate calls for anything that gets
 684     // consumed or borrowed as part of the automatic adjustment
 685     // process.
 686     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 687         let adjustments = self.mc.tables.expr_adjustments(expr);
 688         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 689         for adjustment in adjustments {
 690             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 691             match adjustment.kind {
 692                 adjustment::Adjust::NeverToAny |
 693                 adjustment::Adjust::ReifyFnPointer |
 694                 adjustment::Adjust::UnsafeFnPointer |
 695                 adjustment::Adjust::ClosureFnPointer |
 696                 adjustment::Adjust::MutToConstPointer |
 697                 adjustment::Adjust::Unsize => {
 698                     // Creating a closure/fn-pointer or unsizing consumes
 699                     // the input and stores it into the resulting rvalue.
 700                     self.delegate_consume(expr.id, expr.span, cmt.clone());
 701                 }
 702
 703                 adjustment::Adjust::Deref(None) => {}
 704
 705                 // Autoderefs for overloaded Deref calls in fact reference
 706                 // their receiver. That is, if we have `(*x)` where `x`
 707                 // is of type `Rc<T>`, then this in fact is equivalent to
 708                 // `x.deref()`. Since `deref()` is declared with `&self`,
 709                 // this is an autoref of `x`.
 710                 adjustment::Adjust::Deref(Some(ref deref)) => {
 711                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 712                     self.delegate.borrow(expr.id, expr.span, cmt.clone(),
 713                                          deref.region, bk, AutoRef);
 714                 }
 715
 716                 adjustment::Adjust::Borrow(ref autoref) => {
 717                     self.walk_autoref(expr, cmt.clone(), autoref);
 718                 }
 719             }
 720             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 721         }
 722     }
 723
 724     /// Walks the autoref `autoref` applied to the autoderef'd
 725     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 726     /// after all relevant autoderefs have occurred.
 727     fn walk_autoref(&mut self,
 728                     expr: &hir::Expr,
 729                     cmt_base: mc::cmt<'tcx>,
 730                     autoref: &adjustment::AutoBorrow<'tcx>) {
 731         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 732                expr.id,
 733                cmt_base,
 734                autoref);
 735
 736         match *autoref {
 737             adjustment::AutoBorrow::Ref(r, m) => {
 738                 self.delegate.borrow(expr.id,
 739                                      expr.span,
 740                                      cmt_base,
 741                                      r,
 742                                      ty::BorrowKind::from_mutbl(m),
 743                                      AutoRef);
 744             }
 745
 746             adjustment::AutoBorrow::RawPtr(m) => {
 747                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 748                        expr.id,
 749                        cmt_base);
 750
 751                 // Converting from a &T to *T (or &mut T to *mut T) is
 752                 // treated as borrowing it for the enclosing temporary
 753                 // scope.
 754                 let r = self.tcx().mk_region(ty::ReScope(
 755                     region::Scope::Node(expr.hir_id.local_id)));
 756
 757                 self.delegate.borrow(expr.id,
 758                                      expr.span,
 759                                      cmt_base,
 760                                      r,
 761                                      ty::BorrowKind::from_mutbl(m),
 762                                      AutoUnsafe);
 763             }
 764         }
 765     }
 766
 767     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 768         let mut mode = Unknown;
 769         for pat in &arm.pats {
 770             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 771         }
 772         mode
 773     }
 774
 775     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 776         for pat in &arm.pats {
 777             self.walk_pat(discr_cmt.clone(), &pat, mode);
 778         }
 779
 780         if let Some(ref guard) = arm.guard {
 781             self.consume_expr(&guard);
 782         }
 783
 784         self.consume_expr(&arm.body);
 785     }
 786
 787     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 788     /// arg or let binding.  *Not* a match arm or nested pat.)
 789     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 790         let mut mode = Unknown;
 791         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 792         let mode = mode.match_mode();
 793         self.walk_pat(cmt_discr, pat, mode);
 794     }
 795
 796     /// Identifies any bindings within `pat` and accumulates within
 797     /// `mode` whether the overall pattern/match structure is a move,
 798     /// copy, or borrow.
 799     fn determine_pat_move_mode(&mut self,
 800                                cmt_discr: mc::cmt<'tcx>,
 801                                pat: &hir::Pat,
 802                                mode: &mut TrackMatchMode) {
 803         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 804                pat);
 805         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 806             if let PatKind::Binding(..) = pat.node {
 807                 let bm = *self.mc.tables.pat_binding_modes().get(pat.hir_id)
 808                                                           .expect("missing binding mode");
 809                 match bm {
 810                     ty::BindByReference(..) =>
 811                         mode.lub(BorrowingMatch),
 812                     ty::BindByValue(..) => {
 813                         match copy_or_move(&self.mc, self.param_env, &cmt_pat, PatBindingMove) {
 814                             Copy => mode.lub(CopyingMatch),
 815                             Move(..) => mode.lub(MovingMatch),
 816                         }
 817                     }
 818                 }
 819             }
 820         }));
 821     }
 822
 823     /// The core driver for walking a pattern; `match_mode` must be
 824     /// established up front, e.g. via `determine_pat_move_mode` (see
 825     /// also `walk_irrefutable_pat` for patterns that stand alone).
 826     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 827         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 828
 829         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 830         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 831             if let PatKind::Binding(_, def_id, ..) = pat.node {
 832                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 833                 let bm = *mc.tables.pat_binding_modes().get(pat.hir_id)
 834                                                      .expect("missing binding mode");
 835
 836                 // pat_ty: the type of the binding being produced.
 837                 let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
 838
 839                 // Each match binding is effectively an assignment to the
 840                 // binding being produced.
 841                 let def = Def::Local(def_id);
 842                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 843                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 844                 }
 845
 846                 // It is also a borrow or copy/move of the value being matched.
 847                 match bm {
 848                     ty::BindByReference(m) => {
 849                         if let ty::TyRef(r, _) = pat_ty.sty {
 850                             let bk = ty::BorrowKind::from_mutbl(m);
 851                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 852                         }
 853                     }
 854                     ty::BindByValue(..) => {
 855                         let mode = copy_or_move(mc, param_env, &cmt_pat, PatBindingMove);
 856                         debug!("walk_pat binding consuming pat");
 857                         delegate.consume_pat(pat, cmt_pat, mode);
 858                     }
 859                 }
 860             }
 861         }));
 862
 863         // Do a second pass over the pattern, calling `matched_pat` on
 864         // the interior nodes (enum variants and structs), as opposed
 865         // to the above loop's visit of than the bindings that form
 866         // the leaves of the pattern tree structure.
 867         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 868             let qpath = match pat.node {
 869                 PatKind::Path(ref qpath) |
 870                 PatKind::TupleStruct(ref qpath, ..) |
 871                 PatKind::Struct(ref qpath, ..) => qpath,
 872                 _ => return
 873             };
 874             let def = mc.tables.qpath_def(qpath, pat.hir_id);
 875             match def {
 876                 Def::Variant(variant_did) |
 877                 Def::VariantCtor(variant_did, ..) => {
 878                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 879
 880                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 881                     delegate.matched_pat(pat, downcast_cmt, match_mode);
 882                 }
 883                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 884                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 885                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 886                     delegate.matched_pat(pat, cmt_pat, match_mode);
 887                 }
 888                 _ => {}
 889             }
 890         }));
 891     }
 892
 893     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 894         debug!("walk_captures({:?})", closure_expr);
 895
 896         self.tcx().with_freevars(closure_expr.id, |freevars| {
 897             for freevar in freevars {
 898                 let var_def_id = freevar.def.def_id();
 899                 debug_assert!(var_def_id.is_local());
 900                 let closure_def_id = self.tcx().hir.local_def_id(closure_expr.id);
 901                 let upvar_id = ty::UpvarId {
 902                     var_id: var_def_id.index,
 903                     closure_expr_id: closure_def_id.index
 904                 };
 905                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 906                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 907                                                                    fn_decl_span,
 908                                                                    freevar.def));
 909                 match upvar_capture {
 910                     ty::UpvarCapture::ByValue => {
 911                         let mode = copy_or_move(&self.mc,
 912                                                 self.param_env,
 913                                                 &cmt_var,
 914                                                 CaptureMove);
 915                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 916                     }
 917                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 918                         self.delegate.borrow(closure_expr.id,
 919                                              fn_decl_span,
 920                                              cmt_var,
 921                                              upvar_borrow.region,
 922                                              upvar_borrow.kind,
 923                                              ClosureCapture(freevar.span));
 924                     }
 925                 }
 926             }
 927         });
 928     }
 929
 930     fn cat_captured_var(&mut self,
 931                         closure_id: ast::NodeId,
 932                         closure_span: Span,
 933                         upvar_def: Def)
 934                         -> mc::McResult<mc::cmt<'tcx>> {
 935         // Create the cmt for the variable being borrowed, from the
 936         // caller's perspective
 937         let var_node_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
 938         let var_hir_id = self.tcx().hir.node_to_hir_id(var_node_id);
 939         let var_ty = self.mc.node_ty(var_hir_id)?;
 940         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 941     }
 942 }
 943
 944 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 945                                 param_env: ty::ParamEnv<'tcx>,
 946                                 cmt: &mc::cmt<'tcx>,
 947                                 move_reason: MoveReason)
 948                                 -> ConsumeMode
 949 {
 950     if mc.type_moves_by_default(param_env, cmt.ty, cmt.span) {
 951         Move(move_reason)
 952     } else {
 953         Copy
 954     }
 955 }