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