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 middle::{def, pat_util};
  23 use middle::def_id::{DefId};
  24 use middle::infer;
  25 use middle::mem_categorization as mc;
  26 use middle::ty;
  27 use middle::ty::adjustment;
  28
  29 use rustc_front::hir;
  30
  31 use syntax::ast;
  32 use syntax::ptr::P;
  33 use syntax::codemap::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,
  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: &ty::ctxt, trait_id: DefId)
 213                      -> 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         tcx.sess.bug("overloaded call didn't map to known function trait")
 228     }
 229
 230     fn from_method_id(tcx: &ty::ctxt, method_id: DefId)
 231                       -> OverloadedCallType {
 232         let method = tcx.impl_or_trait_item(method_id);
 233         OverloadedCallType::from_trait_id(tcx, method.container().id())
 234     }
 235 }
 236
 237 ///////////////////////////////////////////////////////////////////////////
 238 // The ExprUseVisitor type
 239 //
 240 // This is the code that actually walks the tree. Like
 241 // mem_categorization, it requires a TYPER, which is a type that
 242 // supplies types from the tree. After type checking is complete, you
 243 // can just use the tcx as the typer.
 244 pub struct ExprUseVisitor<'d, 't, 'a: 't, 'tcx:'a+'d> {
 245     typer: &'t infer::InferCtxt<'a, 'tcx>,
 246     mc: mc::MemCategorizationContext<'t, 'a, 'tcx>,
 247     delegate: &'d mut Delegate<'tcx>,
 248 }
 249
 250 // If the TYPER results in an error, it's because the type check
 251 // failed (or will fail, when the error is uncovered and reported
 252 // during writeback). In this case, we just ignore this part of the
 253 // code.
 254 //
 255 // Note that this macro appears similar to try!(), but, unlike try!(),
 256 // it does not propagate the error.
 257 macro_rules! return_if_err {
 258     ($inp: expr) => (
 259         match $inp {
 260             Ok(v) => v,
 261             Err(()) => {
 262                 debug!("mc reported err");
 263                 return
 264             }
 265         }
 266     )
 267 }
 268
 269 /// Whether the elements of an overloaded operation are passed by value or by reference
 270 enum PassArgs {
 271     ByValue,
 272     ByRef,
 273 }
 274
 275 impl<'d,'t,'a,'tcx> ExprUseVisitor<'d,'t,'a,'tcx> {
 276     pub fn new(delegate: &'d mut (Delegate<'tcx>+'d),
 277                typer: &'t infer::InferCtxt<'a, 'tcx>)
 278                -> ExprUseVisitor<'d,'t,'a,'tcx> where 'tcx:'a+'d
 279     {
 280         let mc: mc::MemCategorizationContext<'t, 'a, 'tcx> =
 281             mc::MemCategorizationContext::new(typer);
 282         ExprUseVisitor { typer: typer, mc: mc, delegate: delegate }
 283     }
 284
 285     pub fn walk_fn(&mut self,
 286                    decl: &hir::FnDecl,
 287                    body: &hir::Block) {
 288         self.walk_arg_patterns(decl, body);
 289         self.walk_block(body);
 290     }
 291
 292     fn walk_arg_patterns(&mut self,
 293                          decl: &hir::FnDecl,
 294                          body: &hir::Block) {
 295         for arg in &decl.inputs {
 296             let arg_ty = return_if_err!(self.typer.node_ty(arg.pat.id));
 297
 298             let fn_body_scope = self.tcx().region_maps.node_extent(body.id);
 299             let arg_cmt = self.mc.cat_rvalue(
 300                 arg.id,
 301                 arg.pat.span,
 302                 ty::ReScope(fn_body_scope), // Args live only as long as the fn body.
 303                 arg_ty);
 304
 305             self.walk_irrefutable_pat(arg_cmt, &*arg.pat);
 306         }
 307     }
 308
 309     fn tcx(&self) -> &'t ty::ctxt<'tcx> {
 310         self.typer.tcx
 311     }
 312
 313     fn delegate_consume(&mut self,
 314                         consume_id: ast::NodeId,
 315                         consume_span: Span,
 316                         cmt: mc::cmt<'tcx>) {
 317         debug!("delegate_consume(consume_id={}, cmt={:?})",
 318                consume_id, cmt);
 319
 320         let mode = copy_or_move(self.typer, &cmt, DirectRefMove);
 321         self.delegate.consume(consume_id, consume_span, cmt, mode);
 322     }
 323
 324     fn consume_exprs(&mut self, exprs: &[P<hir::Expr>]) {
 325         for expr in exprs {
 326             self.consume_expr(&**expr);
 327         }
 328     }
 329
 330     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 331         debug!("consume_expr(expr={:?})", expr);
 332
 333         let cmt = return_if_err!(self.mc.cat_expr(expr));
 334         self.delegate_consume(expr.id, expr.span, cmt);
 335         self.walk_expr(expr);
 336     }
 337
 338     fn mutate_expr(&mut self,
 339                    assignment_expr: &hir::Expr,
 340                    expr: &hir::Expr,
 341                    mode: MutateMode) {
 342         let cmt = return_if_err!(self.mc.cat_expr(expr));
 343         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 344         self.walk_expr(expr);
 345     }
 346
 347     fn borrow_expr(&mut self,
 348                    expr: &hir::Expr,
 349                    r: ty::Region,
 350                    bk: ty::BorrowKind,
 351                    cause: LoanCause) {
 352         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 353                expr, r, bk);
 354
 355         let cmt = return_if_err!(self.mc.cat_expr(expr));
 356         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 357
 358         self.walk_expr(expr)
 359     }
 360
 361     fn select_from_expr(&mut self, expr: &hir::Expr) {
 362         self.walk_expr(expr)
 363     }
 364
 365     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 366         debug!("walk_expr(expr={:?})", expr);
 367
 368         self.walk_adjustment(expr);
 369
 370         match expr.node {
 371             hir::ExprPath(..) => { }
 372
 373             hir::ExprType(ref subexpr, _) => {
 374                 self.walk_expr(&**subexpr)
 375             }
 376
 377             hir::ExprUnary(hir::UnDeref, ref base) => {      // *base
 378                 if !self.walk_overloaded_operator(expr, &**base, Vec::new(), PassArgs::ByRef) {
 379                     self.select_from_expr(&**base);
 380                 }
 381             }
 382
 383             hir::ExprField(ref base, _) => {         // base.f
 384                 self.select_from_expr(&**base);
 385             }
 386
 387             hir::ExprTupField(ref base, _) => {         // base.<n>
 388                 self.select_from_expr(&**base);
 389             }
 390
 391             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 392                 if !self.walk_overloaded_operator(expr,
 393                                                   &**lhs,
 394                                                   vec![&**rhs],
 395                                                   PassArgs::ByValue) {
 396                     self.select_from_expr(&**lhs);
 397                     self.consume_expr(&**rhs);
 398                 }
 399             }
 400
 401             hir::ExprRange(ref start, ref end) => {
 402                 start.as_ref().map(|e| self.consume_expr(&**e));
 403                 end.as_ref().map(|e| self.consume_expr(&**e));
 404             }
 405
 406             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 407                 self.walk_callee(expr, &**callee);
 408                 self.consume_exprs(args);
 409             }
 410
 411             hir::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 412                 self.consume_exprs(args);
 413             }
 414
 415             hir::ExprStruct(_, ref fields, ref opt_with) => {
 416                 self.walk_struct_expr(expr, fields, opt_with);
 417             }
 418
 419             hir::ExprTup(ref exprs) => {
 420                 self.consume_exprs(exprs);
 421             }
 422
 423             hir::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
 424                 self.consume_expr(&**cond_expr);
 425                 self.walk_block(&**then_blk);
 426                 if let Some(ref else_expr) = *opt_else_expr {
 427                     self.consume_expr(&**else_expr);
 428                 }
 429             }
 430
 431             hir::ExprMatch(ref discr, ref arms, _) => {
 432                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
 433                 self.borrow_expr(&**discr, ty::ReEmpty, ty::ImmBorrow, MatchDiscriminant);
 434
 435                 // treatment of the discriminant is handled while walking the arms.
 436                 for arm in arms {
 437                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 438                     let mode = mode.match_mode();
 439                     self.walk_arm(discr_cmt.clone(), arm, mode);
 440                 }
 441             }
 442
 443             hir::ExprVec(ref exprs) => {
 444                 self.consume_exprs(exprs);
 445             }
 446
 447             hir::ExprAddrOf(m, ref base) => {   // &base
 448                 // make sure that the thing we are pointing out stays valid
 449                 // for the lifetime `scope_r` of the resulting ptr:
 450                 let expr_ty = return_if_err!(self.typer.node_ty(expr.id));
 451                 if let ty::TyRef(&r, _) = expr_ty.sty {
 452                     let bk = ty::BorrowKind::from_mutbl(m);
 453                     self.borrow_expr(&**base, r, bk, AddrOf);
 454                 }
 455             }
 456
 457             hir::ExprInlineAsm(ref ia) => {
 458                 for &(_, ref input) in &ia.inputs {
 459                     self.consume_expr(&**input);
 460                 }
 461
 462                 for output in &ia.outputs {
 463                     if output.is_indirect {
 464                         self.consume_expr(&*output.expr);
 465                     } else {
 466                         self.mutate_expr(expr, &*output.expr,
 467                                          if output.is_rw {
 468                                              MutateMode::WriteAndRead
 469                                          } else {
 470                                              MutateMode::JustWrite
 471                                          });
 472                     }
 473                 }
 474             }
 475
 476             hir::ExprBreak(..) |
 477             hir::ExprAgain(..) |
 478             hir::ExprLit(..) => {}
 479
 480             hir::ExprLoop(ref blk, _) => {
 481                 self.walk_block(&**blk);
 482             }
 483
 484             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 485                 self.consume_expr(&**cond_expr);
 486                 self.walk_block(&**blk);
 487             }
 488
 489             hir::ExprUnary(op, ref lhs) => {
 490                 let pass_args = if ::rustc_front::util::is_by_value_unop(op) {
 491                     PassArgs::ByValue
 492                 } else {
 493                     PassArgs::ByRef
 494                 };
 495
 496                 if !self.walk_overloaded_operator(expr, &**lhs, Vec::new(), pass_args) {
 497                     self.consume_expr(&**lhs);
 498                 }
 499             }
 500
 501             hir::ExprBinary(op, ref lhs, ref rhs) => {
 502                 let pass_args = if ::rustc_front::util::is_by_value_binop(op.node) {
 503                     PassArgs::ByValue
 504                 } else {
 505                     PassArgs::ByRef
 506                 };
 507
 508                 if !self.walk_overloaded_operator(expr, &**lhs, vec![&**rhs], pass_args) {
 509                     self.consume_expr(&**lhs);
 510                     self.consume_expr(&**rhs);
 511                 }
 512             }
 513
 514             hir::ExprBlock(ref blk) => {
 515                 self.walk_block(&**blk);
 516             }
 517
 518             hir::ExprRet(ref opt_expr) => {
 519                 if let Some(ref expr) = *opt_expr {
 520                     self.consume_expr(&**expr);
 521                 }
 522             }
 523
 524             hir::ExprAssign(ref lhs, ref rhs) => {
 525                 self.mutate_expr(expr, &**lhs, MutateMode::JustWrite);
 526                 self.consume_expr(&**rhs);
 527             }
 528
 529             hir::ExprCast(ref base, _) => {
 530                 self.consume_expr(&**base);
 531             }
 532
 533             hir::ExprAssignOp(op, ref lhs, ref rhs) => {
 534                 // NB All our assignment operations take the RHS by value
 535                 assert!(::rustc_front::util::is_by_value_binop(op.node));
 536
 537                 if !self.walk_overloaded_operator(expr, lhs, vec![rhs], PassArgs::ByValue) {
 538                     self.mutate_expr(expr, &**lhs, MutateMode::WriteAndRead);
 539                     self.consume_expr(&**rhs);
 540                 }
 541             }
 542
 543             hir::ExprRepeat(ref base, ref count) => {
 544                 self.consume_expr(&**base);
 545                 self.consume_expr(&**count);
 546             }
 547
 548             hir::ExprClosure(..) => {
 549                 self.walk_captures(expr)
 550             }
 551
 552             hir::ExprBox(ref base) => {
 553                 self.consume_expr(&**base);
 554             }
 555         }
 556     }
 557
 558     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 559         let callee_ty = return_if_err!(self.typer.expr_ty_adjusted(callee));
 560         debug!("walk_callee: callee={:?} callee_ty={:?}",
 561                callee, callee_ty);
 562         let call_scope = self.tcx().region_maps.node_extent(call.id);
 563         match callee_ty.sty {
 564             ty::TyBareFn(..) => {
 565                 self.consume_expr(callee);
 566             }
 567             ty::TyError => { }
 568             _ => {
 569                 let overloaded_call_type =
 570                     match self.typer.node_method_id(ty::MethodCall::expr(call.id)) {
 571                         Some(method_id) => {
 572                             OverloadedCallType::from_method_id(self.tcx(), method_id)
 573                         }
 574                         None => {
 575                             self.tcx().sess.span_bug(
 576                                 callee.span,
 577                                 &format!("unexpected callee type {}", callee_ty))
 578                         }
 579                     };
 580                 match overloaded_call_type {
 581                     FnMutOverloadedCall => {
 582                         self.borrow_expr(callee,
 583                                          ty::ReScope(call_scope),
 584                                          ty::MutBorrow,
 585                                          ClosureInvocation);
 586                     }
 587                     FnOverloadedCall => {
 588                         self.borrow_expr(callee,
 589                                          ty::ReScope(call_scope),
 590                                          ty::ImmBorrow,
 591                                          ClosureInvocation);
 592                     }
 593                     FnOnceOverloadedCall => self.consume_expr(callee),
 594                 }
 595             }
 596         }
 597     }
 598
 599     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 600         match stmt.node {
 601             hir::StmtDecl(ref decl, _) => {
 602                 match decl.node {
 603                     hir::DeclLocal(ref local) => {
 604                         self.walk_local(&**local);
 605                     }
 606
 607                     hir::DeclItem(_) => {
 608                         // we don't visit nested items in this visitor,
 609                         // only the fn body we were given.
 610                     }
 611                 }
 612             }
 613
 614             hir::StmtExpr(ref expr, _) |
 615             hir::StmtSemi(ref expr, _) => {
 616                 self.consume_expr(&**expr);
 617             }
 618         }
 619     }
 620
 621     fn walk_local(&mut self, local: &hir::Local) {
 622         match local.init {
 623             None => {
 624                 let delegate = &mut self.delegate;
 625                 pat_util::pat_bindings(&self.typer.tcx.def_map, &*local.pat,
 626                                        |_, id, span, _| {
 627                     delegate.decl_without_init(id, span);
 628                 })
 629             }
 630
 631             Some(ref expr) => {
 632                 // Variable declarations with
 633                 // initializers are considered
 634                 // "assigns", which is handled by
 635                 // `walk_pat`:
 636                 self.walk_expr(&**expr);
 637                 let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
 638                 self.walk_irrefutable_pat(init_cmt, &*local.pat);
 639             }
 640         }
 641     }
 642
 643     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 644     /// depending on its type.
 645     fn walk_block(&mut self, blk: &hir::Block) {
 646         debug!("walk_block(blk.id={})", blk.id);
 647
 648         for stmt in &blk.stmts {
 649             self.walk_stmt(stmt);
 650         }
 651
 652         if let Some(ref tail_expr) = blk.expr {
 653             self.consume_expr(&**tail_expr);
 654         }
 655     }
 656
 657     fn walk_struct_expr(&mut self,
 658                         _expr: &hir::Expr,
 659                         fields: &[hir::Field],
 660                         opt_with: &Option<P<hir::Expr>>) {
 661         // Consume the expressions supplying values for each field.
 662         for field in fields {
 663             self.consume_expr(&*field.expr);
 664         }
 665
 666         let with_expr = match *opt_with {
 667             Some(ref w) => &**w,
 668             None => { return; }
 669         };
 670
 671         let with_cmt = return_if_err!(self.mc.cat_expr(&*with_expr));
 672
 673         // Select just those fields of the `with`
 674         // expression that will actually be used
 675         if let ty::TyStruct(def, substs) = with_cmt.ty.sty {
 676             // Consume those fields of the with expression that are needed.
 677             for with_field in &def.struct_variant().fields {
 678                 if !contains_field_named(with_field, fields) {
 679                     let cmt_field = self.mc.cat_field(
 680                         &*with_expr,
 681                         with_cmt.clone(),
 682                         with_field.name,
 683                         with_field.ty(self.tcx(), substs)
 684                     );
 685                     self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 686                 }
 687             }
 688         } else {
 689             // the base expression should always evaluate to a
 690             // struct; however, when EUV is run during typeck, it
 691             // may not. This will generate an error earlier in typeck,
 692             // so we can just ignore it.
 693             if !self.tcx().sess.has_errors() {
 694                 self.tcx().sess.span_bug(
 695                     with_expr.span,
 696                     "with expression doesn't evaluate to a struct");
 697             }
 698         };
 699
 700         // walk the with expression so that complex expressions
 701         // are properly handled.
 702         self.walk_expr(with_expr);
 703
 704         fn contains_field_named(field: ty::FieldDef,
 705                                 fields: &[hir::Field])
 706                                 -> bool
 707         {
 708             fields.iter().any(
 709                 |f| f.name.node == field.name)
 710         }
 711     }
 712
 713     // Invoke the appropriate delegate calls for anything that gets
 714     // consumed or borrowed as part of the automatic adjustment
 715     // process.
 716     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 717         let typer = self.typer;
 718         //NOTE(@jroesch): mixed RefCell borrow causes crash
 719         let adj = typer.adjustments().get(&expr.id).map(|x| x.clone());
 720         if let Some(adjustment) = adj {
 721             match adjustment {
 722                 adjustment::AdjustReifyFnPointer |
 723                 adjustment::AdjustUnsafeFnPointer => {
 724                     // Creating a closure/fn-pointer or unsizing consumes
 725                     // the input and stores it into the resulting rvalue.
 726                     debug!("walk_adjustment(AdjustReifyFnPointer|AdjustUnsafeFnPointer)");
 727                     let cmt_unadjusted =
 728                         return_if_err!(self.mc.cat_expr_unadjusted(expr));
 729                     self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 730                 }
 731                 adjustment::AdjustDerefRef(ref adj) => {
 732                     self.walk_autoderefref(expr, adj);
 733                 }
 734             }
 735         }
 736     }
 737
 738     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 739     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 740     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 741     fn walk_autoderefs(&mut self,
 742                        expr: &hir::Expr,
 743                        autoderefs: usize) {
 744         debug!("walk_autoderefs expr={:?} autoderefs={}", expr, autoderefs);
 745
 746         for i in 0..autoderefs {
 747             let deref_id = ty::MethodCall::autoderef(expr.id, i as u32);
 748             match self.typer.node_method_ty(deref_id) {
 749                 None => {}
 750                 Some(method_ty) => {
 751                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 752
 753                     // the method call infrastructure should have
 754                     // replaced all late-bound regions with variables:
 755                     let self_ty = method_ty.fn_sig().input(0);
 756                     let self_ty = self.tcx().no_late_bound_regions(&self_ty).unwrap();
 757
 758                     let (m, r) = match self_ty.sty {
 759                         ty::TyRef(r, ref m) => (m.mutbl, r),
 760                         _ => self.tcx().sess.span_bug(expr.span,
 761                                 &format!("bad overloaded deref type {:?}",
 762                                     method_ty))
 763                     };
 764                     let bk = ty::BorrowKind::from_mutbl(m);
 765                     self.delegate.borrow(expr.id, expr.span, cmt,
 766                                          *r, bk, AutoRef);
 767                 }
 768             }
 769         }
 770     }
 771
 772     fn walk_autoderefref(&mut self,
 773                          expr: &hir::Expr,
 774                          adj: &adjustment::AutoDerefRef<'tcx>) {
 775         debug!("walk_autoderefref expr={:?} adj={:?}",
 776                expr,
 777                adj);
 778
 779         self.walk_autoderefs(expr, adj.autoderefs);
 780
 781         let cmt_derefd =
 782             return_if_err!(self.mc.cat_expr_autoderefd(expr, adj.autoderefs));
 783
 784         let cmt_refd =
 785             self.walk_autoref(expr, cmt_derefd, adj.autoref);
 786
 787         if adj.unsize.is_some() {
 788             // Unsizing consumes the thin pointer and produces a fat one.
 789             self.delegate_consume(expr.id, expr.span, cmt_refd);
 790         }
 791     }
 792
 793
 794     /// Walks the autoref `opt_autoref` applied to the autoderef'd
 795     /// `expr`. `cmt_derefd` is the mem-categorized form of `expr`
 796     /// after all relevant autoderefs have occurred. Because AutoRefs
 797     /// can be recursive, this function is recursive: it first walks
 798     /// deeply all the way down the autoref chain, and then processes
 799     /// the autorefs on the way out. At each point, it returns the
 800     /// `cmt` for the rvalue that will be produced by introduced an
 801     /// autoref.
 802     fn walk_autoref(&mut self,
 803                     expr: &hir::Expr,
 804                     cmt_base: mc::cmt<'tcx>,
 805                     opt_autoref: Option<adjustment::AutoRef<'tcx>>)
 806                     -> mc::cmt<'tcx>
 807     {
 808         debug!("walk_autoref(expr.id={} cmt_derefd={:?} opt_autoref={:?})",
 809                expr.id,
 810                cmt_base,
 811                opt_autoref);
 812
 813         let cmt_base_ty = cmt_base.ty;
 814
 815         let autoref = match opt_autoref {
 816             Some(ref autoref) => autoref,
 817             None => {
 818                 // No AutoRef.
 819                 return cmt_base;
 820             }
 821         };
 822
 823         match *autoref {
 824             adjustment::AutoPtr(r, m) => {
 825                 self.delegate.borrow(expr.id,
 826                                      expr.span,
 827                                      cmt_base,
 828                                      *r,
 829                                      ty::BorrowKind::from_mutbl(m),
 830                                      AutoRef);
 831             }
 832
 833             adjustment::AutoUnsafe(m) => {
 834                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 835                        expr.id,
 836                        cmt_base);
 837
 838                 // Converting from a &T to *T (or &mut T to *mut T) is
 839                 // treated as borrowing it for the enclosing temporary
 840                 // scope.
 841                 let r = ty::ReScope(self.tcx().region_maps.node_extent(expr.id));
 842
 843                 self.delegate.borrow(expr.id,
 844                                      expr.span,
 845                                      cmt_base,
 846                                      r,
 847                                      ty::BorrowKind::from_mutbl(m),
 848                                      AutoUnsafe);
 849             }
 850         }
 851
 852         // Construct the categorization for the result of the autoref.
 853         // This is always an rvalue, since we are producing a new
 854         // (temporary) indirection.
 855
 856         let adj_ty = cmt_base_ty.adjust_for_autoref(self.tcx(), opt_autoref);
 857
 858         self.mc.cat_rvalue_node(expr.id, expr.span, adj_ty)
 859     }
 860
 861
 862     // When this returns true, it means that the expression *is* a
 863     // method-call (i.e. via the operator-overload).  This true result
 864     // also implies that walk_overloaded_operator already took care of
 865     // recursively processing the input arguments, and thus the caller
 866     // should not do so.
 867     fn walk_overloaded_operator(&mut self,
 868                                 expr: &hir::Expr,
 869                                 receiver: &hir::Expr,
 870                                 rhs: Vec<&hir::Expr>,
 871                                 pass_args: PassArgs)
 872                                 -> bool
 873     {
 874         if !self.typer.is_method_call(expr.id) {
 875             return false;
 876         }
 877
 878         match pass_args {
 879             PassArgs::ByValue => {
 880                 self.consume_expr(receiver);
 881                 for &arg in &rhs {
 882                     self.consume_expr(arg);
 883                 }
 884
 885                 return true;
 886             },
 887             PassArgs::ByRef => {},
 888         }
 889
 890         self.walk_expr(receiver);
 891
 892         // Arguments (but not receivers) to overloaded operator
 893         // methods are implicitly autoref'd which sadly does not use
 894         // adjustments, so we must hardcode the borrow here.
 895
 896         let r = ty::ReScope(self.tcx().region_maps.node_extent(expr.id));
 897         let bk = ty::ImmBorrow;
 898
 899         for &arg in &rhs {
 900             self.borrow_expr(arg, r, bk, OverloadedOperator);
 901         }
 902         return true;
 903     }
 904
 905     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 906         let mut mode = Unknown;
 907         for pat in &arm.pats {
 908             self.determine_pat_move_mode(discr_cmt.clone(), &**pat, &mut mode);
 909         }
 910         mode
 911     }
 912
 913     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 914         for pat in &arm.pats {
 915             self.walk_pat(discr_cmt.clone(), &**pat, mode);
 916         }
 917
 918         if let Some(ref guard) = arm.guard {
 919             self.consume_expr(&**guard);
 920         }
 921
 922         self.consume_expr(&*arm.body);
 923     }
 924
 925     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 926     /// arg or let binding.  *Not* a match arm or nested pat.)
 927     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 928         let mut mode = Unknown;
 929         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 930         let mode = mode.match_mode();
 931         self.walk_pat(cmt_discr, pat, mode);
 932     }
 933
 934     /// Identifies any bindings within `pat` and accumulates within
 935     /// `mode` whether the overall pattern/match structure is a move,
 936     /// copy, or borrow.
 937     fn determine_pat_move_mode(&mut self,
 938                                cmt_discr: mc::cmt<'tcx>,
 939                                pat: &hir::Pat,
 940                                mode: &mut TrackMatchMode) {
 941         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 942                pat);
 943         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 944             let tcx = self.tcx();
 945             let def_map = &self.tcx().def_map;
 946             if pat_util::pat_is_binding(&def_map.borrow(), pat) {
 947                 match pat.node {
 948                     hir::PatIdent(hir::BindByRef(_), _, _) =>
 949                         mode.lub(BorrowingMatch),
 950                     hir::PatIdent(hir::BindByValue(_), _, _) => {
 951                         match copy_or_move(self.typer, &cmt_pat, PatBindingMove) {
 952                             Copy => mode.lub(CopyingMatch),
 953                             Move(_) => mode.lub(MovingMatch),
 954                         }
 955                     }
 956                     _ => {
 957                         tcx.sess.span_bug(
 958                             pat.span,
 959                             "binding pattern not an identifier");
 960                     }
 961                 }
 962             }
 963         }));
 964     }
 965
 966     /// The core driver for walking a pattern; `match_mode` must be
 967     /// established up front, e.g. via `determine_pat_move_mode` (see
 968     /// also `walk_irrefutable_pat` for patterns that stand alone).
 969     fn walk_pat(&mut self,
 970                 cmt_discr: mc::cmt<'tcx>,
 971                 pat: &hir::Pat,
 972                 match_mode: MatchMode) {
 973         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr,
 974                pat);
 975
 976         let mc = &self.mc;
 977         let typer = self.typer;
 978         let def_map = &self.tcx().def_map;
 979         let delegate = &mut self.delegate;
 980         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 981             if pat_util::pat_is_binding(&def_map.borrow(), pat) {
 982                 let tcx = typer.tcx;
 983
 984                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}",
 985                        cmt_pat,
 986                        pat,
 987                        match_mode);
 988
 989                 // pat_ty: the type of the binding being produced.
 990                 let pat_ty = return_if_err!(typer.node_ty(pat.id));
 991
 992                 // Each match binding is effectively an assignment to the
 993                 // binding being produced.
 994                 let def = def_map.borrow().get(&pat.id).unwrap().full_def();
 995                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
 996                     Ok(binding_cmt) => {
 997                         delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 998                     }
 999                     Err(_) => { }
1000                 }
1001
1002                 // It is also a borrow or copy/move of the value being matched.
1003                 match pat.node {
1004                     hir::PatIdent(hir::BindByRef(m), _, _) => {
1005                         if let ty::TyRef(&r, _) = pat_ty.sty {
1006                             let bk = ty::BorrowKind::from_mutbl(m);
1007                             delegate.borrow(pat.id, pat.span, cmt_pat,
1008                                             r, bk, RefBinding);
1009                         }
1010                     }
1011                     hir::PatIdent(hir::BindByValue(_), _, _) => {
1012                         let mode = copy_or_move(typer, &cmt_pat, PatBindingMove);
1013                         debug!("walk_pat binding consuming pat");
1014                         delegate.consume_pat(pat, cmt_pat, mode);
1015                     }
1016                     _ => {
1017                         tcx.sess.span_bug(
1018                             pat.span,
1019                             "binding pattern not an identifier");
1020                     }
1021                 }
1022             } else {
1023                 match pat.node {
1024                     hir::PatVec(_, Some(ref slice_pat), _) => {
1025                         // The `slice_pat` here creates a slice into
1026                         // the original vector.  This is effectively a
1027                         // borrow of the elements of the vector being
1028                         // matched.
1029
1030                         let (slice_cmt, slice_mutbl, slice_r) =
1031                             return_if_err!(mc.cat_slice_pattern(cmt_pat, &**slice_pat));
1032
1033                         // Note: We declare here that the borrow
1034                         // occurs upon entering the `[...]`
1035                         // pattern. This implies that something like
1036                         // `[a; b]` where `a` is a move is illegal,
1037                         // because the borrow is already in effect.
1038                         // In fact such a move would be safe-ish, but
1039                         // it effectively *requires* that we use the
1040                         // nulling out semantics to indicate when a
1041                         // value has been moved, which we are trying
1042                         // to move away from.  Otherwise, how can we
1043                         // indicate that the first element in the
1044                         // vector has been moved?  Eventually, we
1045                         // could perhaps modify this rule to permit
1046                         // `[..a, b]` where `b` is a move, because in
1047                         // that case we can adjust the length of the
1048                         // original vec accordingly, but we'd have to
1049                         // make trans do the right thing, and it would
1050                         // only work for `Box<[T]>`s. It seems simpler
1051                         // to just require that people call
1052                         // `vec.pop()` or `vec.unshift()`.
1053                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
1054                         delegate.borrow(pat.id, pat.span,
1055                                         slice_cmt, slice_r,
1056                                         slice_bk, RefBinding);
1057                     }
1058                     _ => { }
1059                 }
1060             }
1061         }));
1062
1063         // Do a second pass over the pattern, calling `matched_pat` on
1064         // the interior nodes (enum variants and structs), as opposed
1065         // to the above loop's visit of than the bindings that form
1066         // the leaves of the pattern tree structure.
1067         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
1068             let def_map = def_map.borrow();
1069             let tcx = typer.tcx;
1070
1071             match pat.node {
1072                 hir::PatEnum(_, _) | hir::PatQPath(..) |
1073                 hir::PatIdent(_, _, None) | hir::PatStruct(..) => {
1074                     match def_map.get(&pat.id).map(|d| d.full_def()) {
1075                         None => {
1076                             // no definition found: pat is not a
1077                             // struct or enum pattern.
1078                         }
1079
1080                         Some(def::DefVariant(enum_did, variant_did, _is_struct)) => {
1081                             let downcast_cmt =
1082                                 if tcx.lookup_adt_def(enum_did).is_univariant() {
1083                                     cmt_pat
1084                                 } else {
1085                                     let cmt_pat_ty = cmt_pat.ty;
1086                                     mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1087                                 };
1088
1089                             debug!("variant downcast_cmt={:?} pat={:?}",
1090                                    downcast_cmt,
1091                                    pat);
1092
1093                             delegate.matched_pat(pat, downcast_cmt, match_mode);
1094                         }
1095
1096                         Some(def::DefStruct(..)) | Some(def::DefTy(_, false)) => {
1097                             // A struct (in either the value or type
1098                             // namespace; we encounter the former on
1099                             // e.g. patterns for unit structs).
1100
1101                             debug!("struct cmt_pat={:?} pat={:?}",
1102                                    cmt_pat,
1103                                    pat);
1104
1105                             delegate.matched_pat(pat, cmt_pat, match_mode);
1106                         }
1107
1108                         Some(def::DefConst(..)) |
1109                         Some(def::DefAssociatedConst(..)) |
1110                         Some(def::DefLocal(..)) => {
1111                             // This is a leaf (i.e. identifier binding
1112                             // or constant value to match); thus no
1113                             // `matched_pat` call.
1114                         }
1115
1116                         Some(def @ def::DefTy(_, true)) => {
1117                             // An enum's type -- should never be in a
1118                             // pattern.
1119
1120                             if !tcx.sess.has_errors() {
1121                                 let msg = format!("Pattern has unexpected type: {:?} and type {:?}",
1122                                                   def,
1123                                                   cmt_pat.ty);
1124                                 tcx.sess.span_bug(pat.span, &msg)
1125                             }
1126                         }
1127
1128                         Some(def) => {
1129                             // Remaining cases are e.g. DefFn, to
1130                             // which identifiers within patterns
1131                             // should not resolve. However, we do
1132                             // encouter this when using the
1133                             // expr-use-visitor during typeck. So just
1134                             // ignore it, an error should have been
1135                             // reported.
1136
1137                             if !tcx.sess.has_errors() {
1138                                 let msg = format!("Pattern has unexpected def: {:?} and type {:?}",
1139                                                   def,
1140                                                   cmt_pat.ty);
1141                                 tcx.sess.span_bug(pat.span, &msg[..])
1142                             }
1143                         }
1144                     }
1145                 }
1146
1147                 hir::PatIdent(_, _, Some(_)) => {
1148                     // Do nothing; this is a binding (not an enum
1149                     // variant or struct), and the cat_pattern call
1150                     // will visit the substructure recursively.
1151                 }
1152
1153                 hir::PatWild | hir::PatTup(..) | hir::PatBox(..) |
1154                 hir::PatRegion(..) | hir::PatLit(..) | hir::PatRange(..) |
1155                 hir::PatVec(..) => {
1156                     // Similarly, each of these cases does not
1157                     // correspond to an enum variant or struct, so we
1158                     // do not do any `matched_pat` calls for these
1159                     // cases either.
1160                 }
1161             }
1162         }));
1163     }
1164
1165     fn walk_captures(&mut self, closure_expr: &hir::Expr) {
1166         debug!("walk_captures({:?})", closure_expr);
1167
1168         self.tcx().with_freevars(closure_expr.id, |freevars| {
1169             for freevar in freevars {
1170                 let id_var = freevar.def.var_id();
1171                 let upvar_id = ty::UpvarId { var_id: id_var,
1172                                              closure_expr_id: closure_expr.id };
1173                 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
1174                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1175                                                                    closure_expr.span,
1176                                                                    freevar.def));
1177                 match upvar_capture {
1178                     ty::UpvarCapture::ByValue => {
1179                         let mode = copy_or_move(self.typer, &cmt_var, CaptureMove);
1180                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1181                     }
1182                     ty::UpvarCapture::ByRef(upvar_borrow) => {
1183                         self.delegate.borrow(closure_expr.id,
1184                                              closure_expr.span,
1185                                              cmt_var,
1186                                              upvar_borrow.region,
1187                                              upvar_borrow.kind,
1188                                              ClosureCapture(freevar.span));
1189                     }
1190                 }
1191             }
1192         });
1193     }
1194
1195     fn cat_captured_var(&mut self,
1196                         closure_id: ast::NodeId,
1197                         closure_span: Span,
1198                         upvar_def: def::Def)
1199                         -> mc::McResult<mc::cmt<'tcx>> {
1200         // Create the cmt for the variable being borrowed, from the
1201         // caller's perspective
1202         let var_id = upvar_def.var_id();
1203         let var_ty = try!(self.typer.node_ty(var_id));
1204         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1205     }
1206 }
1207
1208 fn copy_or_move<'a, 'tcx>(typer: &infer::InferCtxt<'a, 'tcx>,
1209                       cmt: &mc::cmt<'tcx>,
1210                       move_reason: MoveReason)
1211                       -> ConsumeMode
1212 {
1213     if typer.type_moves_by_default(cmt.ty, cmt.span) {
1214         Move(move_reason)
1215     } else {
1216         Copy
1217     }
1218 }