src/librustc/middle/expr_use_visitor.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A different sort of visitor for walking fn bodies.  Unlike the
  12 //! normal visitor, which just walks the entire body in one shot, the
  13 //! `ExprUseVisitor` determines how expressions are being used.
  14
  15 pub use self::LoanCause::*;
  16 pub use self::ConsumeMode::*;
  17 pub use self::MoveReason::*;
  18 pub use self::MatchMode::*;
  19 use self::TrackMatchMode::*;
  20 use self::OverloadedCallType::*;
  21
  22 use hir::def::Def;
  23 use hir::def_id::{DefId};
  24 use infer::InferCtxt;
  25 use middle::mem_categorization as mc;
  26 use middle::region::RegionMaps;
  27 use ty::{self, TyCtxt, adjustment};
  28
  29 use hir::{self, PatKind};
  30
  31 use syntax::ast;
  32 use syntax::ptr::P;
  33 use syntax_pos::Span;
  34
  35 ///////////////////////////////////////////////////////////////////////////
  36 // The Delegate trait
  37
  38 /// This trait defines the callbacks you can expect to receive when
  39 /// employing the ExprUseVisitor.
  40 pub trait Delegate<'tcx> {
  41     // The value found at `cmt` is either copied or moved, depending
  42     // on mode.
  43     fn consume(&mut self,
  44                consume_id: ast::NodeId,
  45                consume_span: Span,
  46                cmt: mc::cmt<'tcx>,
  47                mode: ConsumeMode);
  48
  49     // The value found at `cmt` has been determined to match the
  50     // pattern binding `matched_pat`, and its subparts are being
  51     // copied or moved depending on `mode`.  Note that `matched_pat`
  52     // is called on all variant/structs in the pattern (i.e., the
  53     // interior nodes of the pattern's tree structure) while
  54     // consume_pat is called on the binding identifiers in the pattern
  55     // (which are leaves of the pattern's tree structure).
  56     //
  57     // Note that variants/structs and identifiers are disjoint; thus
  58     // `matched_pat` and `consume_pat` are never both called on the
  59     // same input pattern structure (though of `consume_pat` can be
  60     // called on a subpart of an input passed to `matched_pat).
  61     fn matched_pat(&mut self,
  62                    matched_pat: &hir::Pat,
  63                    cmt: mc::cmt<'tcx>,
  64                    mode: MatchMode);
  65
  66     // The value found at `cmt` is either copied or moved via the
  67     // pattern binding `consume_pat`, depending on mode.
  68     fn consume_pat(&mut self,
  69                    consume_pat: &hir::Pat,
  70                    cmt: mc::cmt<'tcx>,
  71                    mode: ConsumeMode);
  72
  73     // The value found at `borrow` is being borrowed at the point
  74     // `borrow_id` for the region `loan_region` with kind `bk`.
  75     fn borrow(&mut self,
  76               borrow_id: ast::NodeId,
  77               borrow_span: Span,
  78               cmt: mc::cmt<'tcx>,
  79               loan_region: ty::Region<'tcx>,
  80               bk: ty::BorrowKind,
  81               loan_cause: LoanCause);
  82
  83     // The local variable `id` is declared but not initialized.
  84     fn decl_without_init(&mut self,
  85                          id: ast::NodeId,
  86                          span: Span);
  87
  88     // The path at `cmt` is being assigned to.
  89     fn mutate(&mut self,
  90               assignment_id: ast::NodeId,
  91               assignment_span: Span,
  92               assignee_cmt: mc::cmt<'tcx>,
  93               mode: MutateMode);
  94 }
  95
  96 #[derive(Copy, Clone, PartialEq, Debug)]
  97 pub enum LoanCause {
  98     ClosureCapture(Span),
  99     AddrOf,
 100     AutoRef,
 101     AutoUnsafe,
 102     RefBinding,
 103     OverloadedOperator,
 104     ClosureInvocation,
 105     ForLoop,
 106     MatchDiscriminant
 107 }
 108
 109 #[derive(Copy, Clone, PartialEq, Debug)]
 110 pub enum ConsumeMode {
 111     Copy,                // reference to x where x has a type that copies
 112     Move(MoveReason),    // reference to x where x has a type that moves
 113 }
 114
 115 #[derive(Copy, Clone, PartialEq, Debug)]
 116 pub enum MoveReason {
 117     DirectRefMove,
 118     PatBindingMove,
 119     CaptureMove,
 120 }
 121
 122 #[derive(Copy, Clone, PartialEq, Debug)]
 123 pub enum MatchMode {
 124     NonBindingMatch,
 125     BorrowingMatch,
 126     CopyingMatch,
 127     MovingMatch,
 128 }
 129
 130 #[derive(Copy, Clone, PartialEq, Debug)]
 131 enum TrackMatchMode {
 132     Unknown,
 133     Definite(MatchMode),
 134     Conflicting,
 135 }
 136
 137 impl TrackMatchMode {
 138     // Builds up the whole match mode for a pattern from its constituent
 139     // parts.  The lattice looks like this:
 140     //
 141     //          Conflicting
 142     //            /     \
 143     //           /       \
 144     //      Borrowing   Moving
 145     //           \       /
 146     //            \     /
 147     //            Copying
 148     //               |
 149     //          NonBinding
 150     //               |
 151     //            Unknown
 152     //
 153     // examples:
 154     //
 155     // * `(_, some_int)` pattern is Copying, since
 156     //   NonBinding + Copying => Copying
 157     //
 158     // * `(some_int, some_box)` pattern is Moving, since
 159     //   Copying + Moving => Moving
 160     //
 161     // * `(ref x, some_box)` pattern is Conflicting, since
 162     //   Borrowing + Moving => Conflicting
 163     //
 164     // Note that the `Unknown` and `Conflicting` states are
 165     // represented separately from the other more interesting
 166     // `Definite` states, which simplifies logic here somewhat.
 167     fn lub(&mut self, mode: MatchMode) {
 168         *self = match (*self, mode) {
 169             // Note that clause order below is very significant.
 170             (Unknown, new) => Definite(new),
 171             (Definite(old), new) if old == new => Definite(old),
 172
 173             (Definite(old), NonBindingMatch) => Definite(old),
 174             (Definite(NonBindingMatch), new) => Definite(new),
 175
 176             (Definite(old), CopyingMatch) => Definite(old),
 177             (Definite(CopyingMatch), new) => Definite(new),
 178
 179             (Definite(_), _) => Conflicting,
 180             (Conflicting, _) => *self,
 181         };
 182     }
 183
 184     fn match_mode(&self) -> MatchMode {
 185         match *self {
 186             Unknown => NonBindingMatch,
 187             Definite(mode) => mode,
 188             Conflicting => {
 189                 // Conservatively return MovingMatch to let the
 190                 // compiler continue to make progress.
 191                 MovingMatch
 192             }
 193         }
 194     }
 195 }
 196
 197 #[derive(Copy, Clone, PartialEq, Debug)]
 198 pub enum MutateMode {
 199     Init,
 200     JustWrite,    // x = y
 201     WriteAndRead, // x += y
 202 }
 203
 204 #[derive(Copy, Clone)]
 205 enum OverloadedCallType {
 206     FnOverloadedCall,
 207     FnMutOverloadedCall,
 208     FnOnceOverloadedCall,
 209 }
 210
 211 impl OverloadedCallType {
 212     fn from_trait_id(tcx: TyCtxt, trait_id: DefId) -> OverloadedCallType {
 213         for &(maybe_function_trait, overloaded_call_type) in &[
 214             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 215             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 216             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 217         ] {
 218             match maybe_function_trait {
 219                 Some(function_trait) if function_trait == trait_id => {
 220                     return overloaded_call_type
 221                 }
 222                 _ => continue,
 223             }
 224         }
 225
 226         bug!("overloaded call didn't map to known function trait")
 227     }
 228
 229     fn from_method_id(tcx: TyCtxt, method_id: DefId) -> OverloadedCallType {
 230         let method = tcx.associated_item(method_id);
 231         OverloadedCallType::from_trait_id(tcx, method.container.id())
 232     }
 233 }
 234
 235 ///////////////////////////////////////////////////////////////////////////
 236 // The ExprUseVisitor type
 237 //
 238 // This is the code that actually walks the tree. Like
 239 // mem_categorization, it requires a TYPER, which is a type that
 240 // supplies types from the tree. After type checking is complete, you
 241 // can just use the tcx as the typer.
 242 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 243     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 244     delegate: &'a mut Delegate<'tcx>,
 245 }
 246
 247 // If the TYPER results in an error, it's because the type check
 248 // failed (or will fail, when the error is uncovered and reported
 249 // during writeback). In this case, we just ignore this part of the
 250 // code.
 251 //
 252 // Note that this macro appears similar to try!(), but, unlike try!(),
 253 // it does not propagate the error.
 254 macro_rules! return_if_err {
 255     ($inp: expr) => (
 256         match $inp {
 257             Ok(v) => v,
 258             Err(()) => {
 259                 debug!("mc reported err");
 260                 return
 261             }
 262         }
 263     )
 264 }
 265
 266 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 267     pub fn new(delegate: &'a mut (Delegate<'tcx>+'a),
 268                region_maps: &'a RegionMaps,
 269                infcx: &'a InferCtxt<'a, 'gcx, 'tcx>)
 270                -> Self
 271     {
 272         ExprUseVisitor::with_options(delegate,
 273                                      infcx,
 274                                      region_maps,
 275                                      mc::MemCategorizationOptions::default())
 276     }
 277
 278     pub fn with_options(delegate: &'a mut (Delegate<'tcx>+'a),
 279                         infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 280                         region_maps: &'a RegionMaps,
 281                         options: mc::MemCategorizationOptions)
 282                -> Self
 283     {
 284         ExprUseVisitor {
 285             mc: mc::MemCategorizationContext::with_options(infcx, region_maps, options),
 286             delegate: delegate
 287         }
 288     }
 289
 290     pub fn consume_body(&mut self, body: &hir::Body) {
 291         debug!("consume_body(body={:?})", body);
 292
 293         for arg in &body.arguments {
 294             let arg_ty = return_if_err!(self.mc.infcx.node_ty(arg.pat.id));
 295
 296             let fn_body_scope_r = self.tcx().node_scope_region(body.value.id);
 297             let arg_cmt = self.mc.cat_rvalue(
 298                 arg.id,
 299                 arg.pat.span,
 300                 fn_body_scope_r, // Args live only as long as the fn body.
 301                 arg_ty);
 302
 303             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 304         }
 305
 306         self.consume_expr(&body.value);
 307     }
 308
 309     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 310         self.mc.infcx.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.mc.infcx, &cmt, DirectRefMove);
 321         self.delegate.consume(consume_id, consume_span, cmt, mode);
 322     }
 323
 324     fn consume_exprs(&mut self, exprs: &[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<'tcx>,
 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                 self.select_from_expr(&base);
 379             }
 380
 381             hir::ExprField(ref base, _) => {         // base.f
 382                 self.select_from_expr(&base);
 383             }
 384
 385             hir::ExprTupField(ref base, _) => {         // base.<n>
 386                 self.select_from_expr(&base);
 387             }
 388
 389             hir::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 390                 self.select_from_expr(&lhs);
 391                 self.consume_expr(&rhs);
 392             }
 393
 394             hir::ExprCall(ref callee, ref args) => {    // callee(args)
 395                 self.walk_callee(expr, &callee);
 396                 self.consume_exprs(args);
 397             }
 398
 399             hir::ExprMethodCall(.., ref args) => { // callee.m(args)
 400                 self.consume_exprs(args);
 401             }
 402
 403             hir::ExprStruct(_, ref fields, ref opt_with) => {
 404                 self.walk_struct_expr(fields, opt_with);
 405             }
 406
 407             hir::ExprTup(ref exprs) => {
 408                 self.consume_exprs(exprs);
 409             }
 410
 411             hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 412                 self.consume_expr(&cond_expr);
 413                 self.walk_expr(&then_expr);
 414                 if let Some(ref else_expr) = *opt_else_expr {
 415                     self.consume_expr(&else_expr);
 416                 }
 417             }
 418
 419             hir::ExprMatch(ref discr, ref arms, _) => {
 420                 let discr_cmt = return_if_err!(self.mc.cat_expr(&discr));
 421                 let r = self.tcx().types.re_empty;
 422                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 423
 424                 // treatment of the discriminant is handled while walking the arms.
 425                 for arm in arms {
 426                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 427                     let mode = mode.match_mode();
 428                     self.walk_arm(discr_cmt.clone(), arm, mode);
 429                 }
 430             }
 431
 432             hir::ExprArray(ref exprs) => {
 433                 self.consume_exprs(exprs);
 434             }
 435
 436             hir::ExprAddrOf(m, ref base) => {   // &base
 437                 // make sure that the thing we are pointing out stays valid
 438                 // for the lifetime `scope_r` of the resulting ptr:
 439                 let expr_ty = return_if_err!(self.mc.infcx.node_ty(expr.id));
 440                 if let ty::TyRef(r, _) = expr_ty.sty {
 441                     let bk = ty::BorrowKind::from_mutbl(m);
 442                     self.borrow_expr(&base, r, bk, AddrOf);
 443                 }
 444             }
 445
 446             hir::ExprInlineAsm(ref ia, ref outputs, ref inputs) => {
 447                 for (o, output) in ia.outputs.iter().zip(outputs) {
 448                     if o.is_indirect {
 449                         self.consume_expr(output);
 450                     } else {
 451                         self.mutate_expr(expr, output,
 452                                          if o.is_rw {
 453                                              MutateMode::WriteAndRead
 454                                          } else {
 455                                              MutateMode::JustWrite
 456                                          });
 457                     }
 458                 }
 459                 self.consume_exprs(inputs);
 460             }
 461
 462             hir::ExprAgain(..) |
 463             hir::ExprLit(..) => {}
 464
 465             hir::ExprLoop(ref blk, _, _) => {
 466                 self.walk_block(&blk);
 467             }
 468
 469             hir::ExprWhile(ref cond_expr, ref blk, _) => {
 470                 self.consume_expr(&cond_expr);
 471                 self.walk_block(&blk);
 472             }
 473
 474             hir::ExprUnary(_, ref lhs) => {
 475                 self.consume_expr(&lhs);
 476             }
 477
 478             hir::ExprBinary(_, ref lhs, ref rhs) => {
 479                 self.consume_expr(&lhs);
 480                 self.consume_expr(&rhs);
 481             }
 482
 483             hir::ExprBlock(ref blk) => {
 484                 self.walk_block(&blk);
 485             }
 486
 487             hir::ExprBreak(_, ref opt_expr) | hir::ExprRet(ref opt_expr) => {
 488                 if let Some(ref expr) = *opt_expr {
 489                     self.consume_expr(&expr);
 490                 }
 491             }
 492
 493             hir::ExprAssign(ref lhs, ref rhs) => {
 494                 self.mutate_expr(expr, &lhs, MutateMode::JustWrite);
 495                 self.consume_expr(&rhs);
 496             }
 497
 498             hir::ExprCast(ref base, _) => {
 499                 self.consume_expr(&base);
 500             }
 501
 502             hir::ExprAssignOp(_, ref lhs, ref rhs) => {
 503                 if self.mc.infcx.tables.borrow().is_method_call(expr) {
 504                     self.consume_expr(lhs);
 505                 } else {
 506                     self.mutate_expr(expr, &lhs, MutateMode::WriteAndRead);
 507                 }
 508                 self.consume_expr(&rhs);
 509             }
 510
 511             hir::ExprRepeat(ref base, _) => {
 512                 self.consume_expr(&base);
 513             }
 514
 515             hir::ExprClosure(.., fn_decl_span) => {
 516                 self.walk_captures(expr, fn_decl_span)
 517             }
 518
 519             hir::ExprBox(ref base) => {
 520                 self.consume_expr(&base);
 521             }
 522         }
 523     }
 524
 525     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 526         let callee_ty = return_if_err!(self.mc.infcx.expr_ty_adjusted(callee));
 527         debug!("walk_callee: callee={:?} callee_ty={:?}",
 528                callee, callee_ty);
 529         match callee_ty.sty {
 530             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 531                 self.consume_expr(callee);
 532             }
 533             ty::TyError => { }
 534             _ => {
 535                 let def_id = self.mc.infcx.tables.borrow().type_dependent_defs[&call.id].def_id();
 536                 match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 537                     FnMutOverloadedCall => {
 538                         let call_scope_r = self.tcx().node_scope_region(call.id);
 539                         self.borrow_expr(callee,
 540                                          call_scope_r,
 541                                          ty::MutBorrow,
 542                                          ClosureInvocation);
 543                     }
 544                     FnOverloadedCall => {
 545                         let call_scope_r = self.tcx().node_scope_region(call.id);
 546                         self.borrow_expr(callee,
 547                                          call_scope_r,
 548                                          ty::ImmBorrow,
 549                                          ClosureInvocation);
 550                     }
 551                     FnOnceOverloadedCall => self.consume_expr(callee),
 552                 }
 553             }
 554         }
 555     }
 556
 557     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 558         match stmt.node {
 559             hir::StmtDecl(ref decl, _) => {
 560                 match decl.node {
 561                     hir::DeclLocal(ref local) => {
 562                         self.walk_local(&local);
 563                     }
 564
 565                     hir::DeclItem(_) => {
 566                         // we don't visit nested items in this visitor,
 567                         // only the fn body we were given.
 568                     }
 569                 }
 570             }
 571
 572             hir::StmtExpr(ref expr, _) |
 573             hir::StmtSemi(ref expr, _) => {
 574                 self.consume_expr(&expr);
 575             }
 576         }
 577     }
 578
 579     fn walk_local(&mut self, local: &hir::Local) {
 580         match local.init {
 581             None => {
 582                 let delegate = &mut self.delegate;
 583                 local.pat.each_binding(|_, id, span, _| {
 584                     delegate.decl_without_init(id, span);
 585                 })
 586             }
 587
 588             Some(ref expr) => {
 589                 // Variable declarations with
 590                 // initializers are considered
 591                 // "assigns", which is handled by
 592                 // `walk_pat`:
 593                 self.walk_expr(&expr);
 594                 let init_cmt = return_if_err!(self.mc.cat_expr(&expr));
 595                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 596             }
 597         }
 598     }
 599
 600     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 601     /// depending on its type.
 602     fn walk_block(&mut self, blk: &hir::Block) {
 603         debug!("walk_block(blk.id={})", blk.id);
 604
 605         for stmt in &blk.stmts {
 606             self.walk_stmt(stmt);
 607         }
 608
 609         if let Some(ref tail_expr) = blk.expr {
 610             self.consume_expr(&tail_expr);
 611         }
 612     }
 613
 614     fn walk_struct_expr(&mut self,
 615                         fields: &[hir::Field],
 616                         opt_with: &Option<P<hir::Expr>>) {
 617         // Consume the expressions supplying values for each field.
 618         for field in fields {
 619             self.consume_expr(&field.expr);
 620         }
 621
 622         let with_expr = match *opt_with {
 623             Some(ref w) => &**w,
 624             None => { return; }
 625         };
 626
 627         let with_cmt = return_if_err!(self.mc.cat_expr(&with_expr));
 628
 629         // Select just those fields of the `with`
 630         // expression that will actually be used
 631         match with_cmt.ty.sty {
 632             ty::TyAdt(adt, substs) if adt.is_struct() => {
 633                 // Consume those fields of the with expression that are needed.
 634                 for with_field in &adt.struct_variant().fields {
 635                     if !contains_field_named(with_field, fields) {
 636                         let cmt_field = self.mc.cat_field(
 637                             &*with_expr,
 638                             with_cmt.clone(),
 639                             with_field.name,
 640                             with_field.ty(self.tcx(), substs)
 641                         );
 642                         self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 643                     }
 644                 }
 645             }
 646             _ => {
 647                 // the base expression should always evaluate to a
 648                 // struct; however, when EUV is run during typeck, it
 649                 // may not. This will generate an error earlier in typeck,
 650                 // so we can just ignore it.
 651                 if !self.tcx().sess.has_errors() {
 652                     span_bug!(
 653                         with_expr.span,
 654                         "with expression doesn't evaluate to a struct");
 655                 }
 656             }
 657         }
 658
 659         // walk the with expression so that complex expressions
 660         // are properly handled.
 661         self.walk_expr(with_expr);
 662
 663         fn contains_field_named(field: &ty::FieldDef,
 664                                 fields: &[hir::Field])
 665                                 -> bool
 666         {
 667             fields.iter().any(
 668                 |f| f.name.node == field.name)
 669         }
 670     }
 671
 672     // Invoke the appropriate delegate calls for anything that gets
 673     // consumed or borrowed as part of the automatic adjustment
 674     // process.
 675     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 676         //NOTE(@jroesch): mixed RefCell borrow causes crash
 677         let adjustments = self.mc.infcx.tables.borrow().expr_adjustments(expr).to_vec();
 678         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 679         for adjustment in adjustments {
 680             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 681             match adjustment.kind {
 682                 adjustment::Adjust::NeverToAny |
 683                 adjustment::Adjust::ReifyFnPointer |
 684                 adjustment::Adjust::UnsafeFnPointer |
 685                 adjustment::Adjust::ClosureFnPointer |
 686                 adjustment::Adjust::MutToConstPointer |
 687                 adjustment::Adjust::Unsize => {
 688                     // Creating a closure/fn-pointer or unsizing consumes
 689                     // the input and stores it into the resulting rvalue.
 690                     self.delegate_consume(expr.id, expr.span, cmt.clone());
 691                 }
 692
 693                 adjustment::Adjust::Deref(None) => {}
 694
 695                 // Autoderefs for overloaded Deref calls in fact reference
 696                 // their receiver. That is, if we have `(*x)` where `x`
 697                 // is of type `Rc<T>`, then this in fact is equivalent to
 698                 // `x.deref()`. Since `deref()` is declared with `&self`,
 699                 // this is an autoref of `x`.
 700                 adjustment::Adjust::Deref(Some(ref deref)) => {
 701                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 702                     self.delegate.borrow(expr.id, expr.span, cmt.clone(),
 703                                          deref.region, bk, AutoRef);
 704                 }
 705
 706                 adjustment::Adjust::Borrow(ref autoref) => {
 707                     self.walk_autoref(expr, cmt.clone(), autoref);
 708                 }
 709             }
 710             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 711         }
 712     }
 713
 714     /// Walks the autoref `autoref` applied to the autoderef'd
 715     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 716     /// after all relevant autoderefs have occurred.
 717     fn walk_autoref(&mut self,
 718                     expr: &hir::Expr,
 719                     cmt_base: mc::cmt<'tcx>,
 720                     autoref: &adjustment::AutoBorrow<'tcx>) {
 721         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 722                expr.id,
 723                cmt_base,
 724                autoref);
 725
 726         match *autoref {
 727             adjustment::AutoBorrow::Ref(r, m) => {
 728                 self.delegate.borrow(expr.id,
 729                                      expr.span,
 730                                      cmt_base,
 731                                      r,
 732                                      ty::BorrowKind::from_mutbl(m),
 733                                      AutoRef);
 734             }
 735
 736             adjustment::AutoBorrow::RawPtr(m) => {
 737                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 738                        expr.id,
 739                        cmt_base);
 740
 741                 // Converting from a &T to *T (or &mut T to *mut T) is
 742                 // treated as borrowing it for the enclosing temporary
 743                 // scope.
 744                 let r = self.tcx().node_scope_region(expr.id);
 745
 746                 self.delegate.borrow(expr.id,
 747                                      expr.span,
 748                                      cmt_base,
 749                                      r,
 750                                      ty::BorrowKind::from_mutbl(m),
 751                                      AutoUnsafe);
 752             }
 753         }
 754     }
 755
 756     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 757         let mut mode = Unknown;
 758         for pat in &arm.pats {
 759             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 760         }
 761         mode
 762     }
 763
 764     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 765         for pat in &arm.pats {
 766             self.walk_pat(discr_cmt.clone(), &pat, mode);
 767         }
 768
 769         if let Some(ref guard) = arm.guard {
 770             self.consume_expr(&guard);
 771         }
 772
 773         self.consume_expr(&arm.body);
 774     }
 775
 776     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 777     /// arg or let binding.  *Not* a match arm or nested pat.)
 778     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 779         let mut mode = Unknown;
 780         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 781         let mode = mode.match_mode();
 782         self.walk_pat(cmt_discr, pat, mode);
 783     }
 784
 785     /// Identifies any bindings within `pat` and accumulates within
 786     /// `mode` whether the overall pattern/match structure is a move,
 787     /// copy, or borrow.
 788     fn determine_pat_move_mode(&mut self,
 789                                cmt_discr: mc::cmt<'tcx>,
 790                                pat: &hir::Pat,
 791                                mode: &mut TrackMatchMode) {
 792         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr,
 793                pat);
 794         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 795             match pat.node {
 796                 PatKind::Binding(hir::BindByRef(..), ..) =>
 797                     mode.lub(BorrowingMatch),
 798                 PatKind::Binding(hir::BindByValue(..), ..) => {
 799                     match copy_or_move(self.mc.infcx, &cmt_pat, PatBindingMove) {
 800                         Copy => mode.lub(CopyingMatch),
 801                         Move(..) => mode.lub(MovingMatch),
 802                     }
 803                 }
 804                 _ => {}
 805             }
 806         }));
 807     }
 808
 809     /// The core driver for walking a pattern; `match_mode` must be
 810     /// established up front, e.g. via `determine_pat_move_mode` (see
 811     /// also `walk_irrefutable_pat` for patterns that stand alone).
 812     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 813         debug!("walk_pat cmt_discr={:?} pat={:?}", cmt_discr, pat);
 814
 815         let tcx = &self.tcx();
 816         let mc = &self.mc;
 817         let infcx = self.mc.infcx;
 818         let delegate = &mut self.delegate;
 819         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 820             if let PatKind::Binding(bmode, def_id, ..) = pat.node {
 821                 debug!("binding cmt_pat={:?} pat={:?} match_mode={:?}", cmt_pat, pat, match_mode);
 822
 823                 // pat_ty: the type of the binding being produced.
 824                 let pat_ty = return_if_err!(infcx.node_ty(pat.id));
 825
 826                 // Each match binding is effectively an assignment to the
 827                 // binding being produced.
 828                 let def = Def::Local(def_id);
 829                 if let Ok(binding_cmt) = mc.cat_def(pat.id, pat.span, pat_ty, def) {
 830                     delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 831                 }
 832
 833                 // It is also a borrow or copy/move of the value being matched.
 834                 match bmode {
 835                     hir::BindByRef(m) => {
 836                         if let ty::TyRef(r, _) = pat_ty.sty {
 837                             let bk = ty::BorrowKind::from_mutbl(m);
 838                             delegate.borrow(pat.id, pat.span, cmt_pat, r, bk, RefBinding);
 839                         }
 840                     }
 841                     hir::BindByValue(..) => {
 842                         let mode = copy_or_move(infcx, &cmt_pat, PatBindingMove);
 843                         debug!("walk_pat binding consuming pat");
 844                         delegate.consume_pat(pat, cmt_pat, mode);
 845                     }
 846                 }
 847             }
 848         }));
 849
 850         // Do a second pass over the pattern, calling `matched_pat` on
 851         // the interior nodes (enum variants and structs), as opposed
 852         // to the above loop's visit of than the bindings that form
 853         // the leaves of the pattern tree structure.
 854         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
 855             let qpath = match pat.node {
 856                 PatKind::Path(ref qpath) |
 857                 PatKind::TupleStruct(ref qpath, ..) |
 858                 PatKind::Struct(ref qpath, ..) => qpath,
 859                 _ => return
 860             };
 861             let def = infcx.tables.borrow().qpath_def(qpath, pat.id);
 862             match def {
 863                 Def::Variant(variant_did) |
 864                 Def::VariantCtor(variant_did, ..) => {
 865                     let enum_did = tcx.parent_def_id(variant_did).unwrap();
 866                     let downcast_cmt = if tcx.adt_def(enum_did).is_univariant() {
 867                         cmt_pat
 868                     } else {
 869                         let cmt_pat_ty = cmt_pat.ty;
 870                         mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
 871                     };
 872
 873                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 874                     delegate.matched_pat(pat, downcast_cmt, match_mode);
 875                 }
 876                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 877                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 878                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 879                     delegate.matched_pat(pat, cmt_pat, match_mode);
 880                 }
 881                 _ => {}
 882             }
 883         }));
 884     }
 885
 886     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 887         debug!("walk_captures({:?})", closure_expr);
 888
 889         self.tcx().with_freevars(closure_expr.id, |freevars| {
 890             for freevar in freevars {
 891                 let def_id = freevar.def.def_id();
 892                 let id_var = self.tcx().hir.as_local_node_id(def_id).unwrap();
 893                 let upvar_id = ty::UpvarId { var_id: id_var,
 894                                              closure_expr_id: closure_expr.id };
 895                 let upvar_capture = self.mc.infcx.upvar_capture(upvar_id).unwrap();
 896                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
 897                                                                    fn_decl_span,
 898                                                                    freevar.def));
 899                 match upvar_capture {
 900                     ty::UpvarCapture::ByValue => {
 901                         let mode = copy_or_move(self.mc.infcx, &cmt_var, CaptureMove);
 902                         self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
 903                     }
 904                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 905                         self.delegate.borrow(closure_expr.id,
 906                                              fn_decl_span,
 907                                              cmt_var,
 908                                              upvar_borrow.region,
 909                                              upvar_borrow.kind,
 910                                              ClosureCapture(freevar.span));
 911                     }
 912                 }
 913             }
 914         });
 915     }
 916
 917     fn cat_captured_var(&mut self,
 918                         closure_id: ast::NodeId,
 919                         closure_span: Span,
 920                         upvar_def: Def)
 921                         -> mc::McResult<mc::cmt<'tcx>> {
 922         // Create the cmt for the variable being borrowed, from the
 923         // caller's perspective
 924         let var_id = self.tcx().hir.as_local_node_id(upvar_def.def_id()).unwrap();
 925         let var_ty = self.mc.infcx.node_ty(var_id)?;
 926         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
 927     }
 928 }
 929
 930 fn copy_or_move<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 931                                 cmt: &mc::cmt<'tcx>,
 932                                 move_reason: MoveReason)
 933                                 -> ConsumeMode
 934 {
 935     if infcx.type_moves_by_default(cmt.ty, cmt.span) {
 936         Move(move_reason)
 937     } else {
 938         Copy
 939     }
 940 }