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::MutateMode::*;
  16 pub use self::LoanCause::*;
  17 pub use self::ConsumeMode::*;
  18 pub use self::MoveReason::*;
  19 pub use self::MatchMode::*;
  20 use self::TrackMatchMode::*;
  21 use self::OverloadedCallType::*;
  22
  23 use middle::{def, region, pat_util};
  24 use middle::mem_categorization as mc;
  25 use middle::mem_categorization::Typer;
  26 use middle::ty::{mod, Ty};
  27 use middle::ty::{MethodCall, MethodObject, MethodTraitObject};
  28 use middle::ty::{MethodOrigin, MethodParam, MethodTypeParam};
  29 use middle::ty::{MethodStatic, MethodStaticUnboxedClosure};
  30 use util::ppaux::Repr;
  31
  32 use syntax::ast;
  33 use syntax::ptr::P;
  34 use syntax::codemap::Span;
  35
  36 ///////////////////////////////////////////////////////////////////////////
  37 // The Delegate trait
  38
  39 /// This trait defines the callbacks you can expect to receive when
  40 /// employing the ExprUseVisitor.
  41 pub trait Delegate<'tcx> {
  42     // The value found at `cmt` is either copied or moved, depending
  43     // on mode.
  44     fn consume(&mut self,
  45                consume_id: ast::NodeId,
  46                consume_span: Span,
  47                cmt: mc::cmt<'tcx>,
  48                mode: ConsumeMode);
  49
  50     // The value found at `cmt` has been determined to match the
  51     // pattern binding `matched_pat`, and its subparts are being
  52     // copied or moved depending on `mode`.  Note that `matched_pat`
  53     // is called on all variant/structs in the pattern (i.e., the
  54     // interior nodes of the pattern's tree structure) while
  55     // consume_pat is called on the binding identifiers in the pattern
  56     // (which are leaves of the pattern's tree structure).
  57     //
  58     // Note that variants/structs and identifiers are disjoint; thus
  59     // `matched_pat` and `consume_pat` are never both called on the
  60     // same input pattern structure (though of `consume_pat` can be
  61     // called on a subpart of an input passed to `matched_pat).
  62     fn matched_pat(&mut self,
  63                    matched_pat: &ast::Pat,
  64                    cmt: mc::cmt<'tcx>,
  65                    mode: MatchMode);
  66
  67     // The value found at `cmt` is either copied or moved via the
  68     // pattern binding `consume_pat`, depending on mode.
  69     fn consume_pat(&mut self,
  70                    consume_pat: &ast::Pat,
  71                    cmt: mc::cmt<'tcx>,
  72                    mode: ConsumeMode);
  73
  74     // The value found at `borrow` is being borrowed at the point
  75     // `borrow_id` for the region `loan_region` with kind `bk`.
  76     fn borrow(&mut self,
  77               borrow_id: ast::NodeId,
  78               borrow_span: Span,
  79               cmt: mc::cmt<'tcx>,
  80               loan_region: ty::Region,
  81               bk: ty::BorrowKind,
  82               loan_cause: LoanCause);
  83
  84     // The local variable `id` is declared but not initialized.
  85     fn decl_without_init(&mut self,
  86                          id: ast::NodeId,
  87                          span: Span);
  88
  89     // The path at `cmt` is being assigned to.
  90     fn mutate(&mut self,
  91               assignment_id: ast::NodeId,
  92               assignment_span: Span,
  93               assignee_cmt: mc::cmt<'tcx>,
  94               mode: MutateMode);
  95 }
  96
  97 #[deriving(PartialEq, Show)]
  98 pub enum LoanCause {
  99     ClosureCapture(Span),
 100     AddrOf,
 101     AutoRef,
 102     RefBinding,
 103     OverloadedOperator,
 104     ClosureInvocation,
 105     ForLoop,
 106     MatchDiscriminant
 107 }
 108
 109 #[deriving(PartialEq, Show)]
 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 #[deriving(PartialEq,Show)]
 116 pub enum MoveReason {
 117     DirectRefMove,
 118     PatBindingMove,
 119     CaptureMove,
 120 }
 121
 122 #[deriving(PartialEq,Show)]
 123 pub enum MatchMode {
 124     NonBindingMatch,
 125     BorrowingMatch,
 126     CopyingMatch,
 127     MovingMatch,
 128 }
 129
 130 #[deriving(PartialEq,Show)]
 131 enum TrackMatchMode<T> {
 132     Unknown, Definite(MatchMode), Conflicting,
 133 }
 134
 135 impl<T> TrackMatchMode<T> {
 136     // Builds up the whole match mode for a pattern from its constituent
 137     // parts.  The lattice looks like this:
 138     //
 139     //          Conflicting
 140     //            /     \
 141     //           /       \
 142     //      Borrowing   Moving
 143     //           \       /
 144     //            \     /
 145     //            Copying
 146     //               |
 147     //          NonBinding
 148     //               |
 149     //            Unknown
 150     //
 151     // examples:
 152     //
 153     // * `(_, some_int)` pattern is Copying, since
 154     //   NonBinding + Copying => Copying
 155     //
 156     // * `(some_int, some_box)` pattern is Moving, since
 157     //   Copying + Moving => Moving
 158     //
 159     // * `(ref x, some_box)` pattern is Conflicting, since
 160     //   Borrowing + Moving => Conflicting
 161     //
 162     // Note that the `Unknown` and `Conflicting` states are
 163     // represented separately from the other more interesting
 164     // `Definite` states, which simplifies logic here somewhat.
 165     fn lub(&mut self, mode: MatchMode) {
 166         *self = match (*self, mode) {
 167             // Note that clause order below is very significant.
 168             (Unknown, new) => Definite(new),
 169             (Definite(old), new) if old == new => Definite(old),
 170
 171             (Definite(old), NonBindingMatch) => Definite(old),
 172             (Definite(NonBindingMatch), new) => Definite(new),
 173
 174             (Definite(old), CopyingMatch) => Definite(old),
 175             (Definite(CopyingMatch), new) => Definite(new),
 176
 177             (Definite(_), _) => Conflicting,
 178             (Conflicting, _) => *self,
 179         };
 180     }
 181
 182     fn match_mode(&self) -> MatchMode {
 183         match *self {
 184             Unknown => NonBindingMatch,
 185             Definite(mode) => mode,
 186             Conflicting => {
 187                 // Conservatively return MovingMatch to let the
 188                 // compiler continue to make progress.
 189                 MovingMatch
 190             }
 191         }
 192     }
 193 }
 194
 195 #[deriving(PartialEq,Show)]
 196 pub enum MutateMode {
 197     Init,
 198     JustWrite,    // x = y
 199     WriteAndRead, // x += y
 200 }
 201
 202 enum OverloadedCallType {
 203     FnOverloadedCall,
 204     FnMutOverloadedCall,
 205     FnOnceOverloadedCall,
 206 }
 207
 208 impl OverloadedCallType {
 209     fn from_trait_id(tcx: &ty::ctxt, trait_id: ast::DefId)
 210                      -> OverloadedCallType {
 211         for &(maybe_function_trait, overloaded_call_type) in [
 212             (tcx.lang_items.fn_once_trait(), FnOnceOverloadedCall),
 213             (tcx.lang_items.fn_mut_trait(), FnMutOverloadedCall),
 214             (tcx.lang_items.fn_trait(), FnOverloadedCall)
 215         ].iter() {
 216             match maybe_function_trait {
 217                 Some(function_trait) if function_trait == trait_id => {
 218                     return overloaded_call_type
 219                 }
 220                 _ => continue,
 221             }
 222         }
 223
 224         tcx.sess.bug("overloaded call didn't map to known function trait")
 225     }
 226
 227     fn from_method_id(tcx: &ty::ctxt, method_id: ast::DefId)
 228                       -> OverloadedCallType {
 229         let method_descriptor = match ty::impl_or_trait_item(tcx, method_id) {
 230             ty::MethodTraitItem(ref method_descriptor) => {
 231                 (*method_descriptor).clone()
 232             }
 233             ty::TypeTraitItem(_) => {
 234                 tcx.sess.bug("overloaded call method wasn't in method map")
 235             }
 236         };
 237         let impl_id = match method_descriptor.container {
 238             ty::TraitContainer(_) => {
 239                 tcx.sess.bug("statically resolved overloaded call method \
 240                               belonged to a trait?!")
 241             }
 242             ty::ImplContainer(impl_id) => impl_id,
 243         };
 244         let trait_ref = match ty::impl_trait_ref(tcx, impl_id) {
 245             None => {
 246                 tcx.sess.bug("statically resolved overloaded call impl \
 247                               didn't implement a trait?!")
 248             }
 249             Some(ref trait_ref) => (*trait_ref).clone(),
 250         };
 251         OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 252     }
 253
 254     fn from_unboxed_closure(tcx: &ty::ctxt, closure_did: ast::DefId)
 255                             -> OverloadedCallType {
 256         let trait_did =
 257             tcx.unboxed_closures
 258                .borrow()
 259                .get(&closure_did)
 260                .expect("OverloadedCallType::from_unboxed_closure: didn't \
 261                         find closure id")
 262                .kind
 263                .trait_did(tcx);
 264         OverloadedCallType::from_trait_id(tcx, trait_did)
 265     }
 266
 267     fn from_method_origin(tcx: &ty::ctxt, origin: &MethodOrigin)
 268                           -> OverloadedCallType {
 269         match *origin {
 270             MethodStatic(def_id) => {
 271                 OverloadedCallType::from_method_id(tcx, def_id)
 272             }
 273             MethodStaticUnboxedClosure(def_id) => {
 274                 OverloadedCallType::from_unboxed_closure(tcx, def_id)
 275             }
 276             MethodTypeParam(MethodParam { ref trait_ref, .. }) |
 277             MethodTraitObject(MethodObject { ref trait_ref, .. }) => {
 278                 OverloadedCallType::from_trait_id(tcx, trait_ref.def_id)
 279             }
 280         }
 281     }
 282 }
 283
 284 ///////////////////////////////////////////////////////////////////////////
 285 // The ExprUseVisitor type
 286 //
 287 // This is the code that actually walks the tree. Like
 288 // mem_categorization, it requires a TYPER, which is a type that
 289 // supplies types from the tree. After type checking is complete, you
 290 // can just use the tcx as the typer.
 291
 292 pub struct ExprUseVisitor<'d,'t,'tcx,TYPER:'t> {
 293     typer: &'t TYPER,
 294     mc: mc::MemCategorizationContext<'t,TYPER>,
 295     delegate: &'d mut (Delegate<'tcx>+'d),
 296 }
 297
 298 // If the TYPER results in an error, it's because the type check
 299 // failed (or will fail, when the error is uncovered and reported
 300 // during writeback). In this case, we just ignore this part of the
 301 // code.
 302 //
 303 // Note that this macro appears similar to try!(), but, unlike try!(),
 304 // it does not propagate the error.
 305 macro_rules! return_if_err(
 306     ($inp: expr) => (
 307         match $inp {
 308             Ok(v) => v,
 309             Err(()) => return
 310         }
 311     )
 312 )
 313
 314 impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
 315     pub fn new(delegate: &'d mut Delegate<'tcx>,
 316                typer: &'t TYPER)
 317                -> ExprUseVisitor<'d,'t,'tcx,TYPER> {
 318         ExprUseVisitor { typer: typer,
 319                          mc: mc::MemCategorizationContext::new(typer),
 320                          delegate: delegate }
 321     }
 322
 323     pub fn walk_fn(&mut self,
 324                    decl: &ast::FnDecl,
 325                    body: &ast::Block) {
 326         self.walk_arg_patterns(decl, body);
 327         self.walk_block(body);
 328     }
 329
 330     fn walk_arg_patterns(&mut self,
 331                          decl: &ast::FnDecl,
 332                          body: &ast::Block) {
 333         for arg in decl.inputs.iter() {
 334             let arg_ty = return_if_err!(self.typer.node_ty(arg.pat.id));
 335
 336             let fn_body_scope = region::CodeExtent::from_node_id(body.id);
 337             let arg_cmt = self.mc.cat_rvalue(
 338                 arg.id,
 339                 arg.pat.span,
 340                 ty::ReScope(fn_body_scope), // Args live only as long as the fn body.
 341                 arg_ty);
 342
 343             self.walk_irrefutable_pat(arg_cmt, &*arg.pat);
 344         }
 345     }
 346
 347     fn tcx(&self) -> &'t ty::ctxt<'tcx> {
 348         self.typer.tcx()
 349     }
 350
 351     fn delegate_consume(&mut self,
 352                         consume_id: ast::NodeId,
 353                         consume_span: Span,
 354                         cmt: mc::cmt<'tcx>) {
 355         let mode = copy_or_move(self.tcx(), cmt.ty, DirectRefMove);
 356         self.delegate.consume(consume_id, consume_span, cmt, mode);
 357     }
 358
 359     fn consume_exprs(&mut self, exprs: &Vec<P<ast::Expr>>) {
 360         for expr in exprs.iter() {
 361             self.consume_expr(&**expr);
 362         }
 363     }
 364
 365     pub fn consume_expr(&mut self, expr: &ast::Expr) {
 366         debug!("consume_expr(expr={})", expr.repr(self.tcx()));
 367
 368         let cmt = return_if_err!(self.mc.cat_expr(expr));
 369         self.delegate_consume(expr.id, expr.span, cmt);
 370         self.walk_expr(expr);
 371     }
 372
 373     fn mutate_expr(&mut self,
 374                    assignment_expr: &ast::Expr,
 375                    expr: &ast::Expr,
 376                    mode: MutateMode) {
 377         let cmt = return_if_err!(self.mc.cat_expr(expr));
 378         self.delegate.mutate(assignment_expr.id, assignment_expr.span, cmt, mode);
 379         self.walk_expr(expr);
 380     }
 381
 382     fn borrow_expr(&mut self,
 383                    expr: &ast::Expr,
 384                    r: ty::Region,
 385                    bk: ty::BorrowKind,
 386                    cause: LoanCause) {
 387         debug!("borrow_expr(expr={}, r={}, bk={})",
 388                expr.repr(self.tcx()), r.repr(self.tcx()), bk.repr(self.tcx()));
 389
 390         let cmt = return_if_err!(self.mc.cat_expr(expr));
 391         self.delegate.borrow(expr.id, expr.span, cmt, r, bk, cause);
 392
 393         // Note: Unlike consume, we can ignore ExprParen. cat_expr
 394         // already skips over them, and walk will uncover any
 395         // attachments or whatever.
 396         self.walk_expr(expr)
 397     }
 398
 399     fn select_from_expr(&mut self, expr: &ast::Expr) {
 400         self.walk_expr(expr)
 401     }
 402
 403     pub fn walk_expr(&mut self, expr: &ast::Expr) {
 404         debug!("walk_expr(expr={})", expr.repr(self.tcx()));
 405
 406         self.walk_adjustment(expr);
 407
 408         match expr.node {
 409             ast::ExprParen(ref subexpr) => {
 410                 self.walk_expr(&**subexpr)
 411             }
 412
 413             ast::ExprPath(..) => { }
 414
 415             ast::ExprUnary(ast::UnDeref, ref base) => {      // *base
 416                 if !self.walk_overloaded_operator(expr, &**base, Vec::new()) {
 417                     self.select_from_expr(&**base);
 418                 }
 419             }
 420
 421             ast::ExprField(ref base, _) => {         // base.f
 422                 self.select_from_expr(&**base);
 423             }
 424
 425             ast::ExprTupField(ref base, _) => {         // base.<n>
 426                 self.select_from_expr(&**base);
 427             }
 428
 429             ast::ExprIndex(ref lhs, ref rhs) => {       // lhs[rhs]
 430                 if !self.walk_overloaded_operator(expr, &**lhs, vec![&**rhs]) {
 431                     self.select_from_expr(&**lhs);
 432                     self.consume_expr(&**rhs);
 433                 }
 434             }
 435
 436             ast::ExprSlice(ref base, ref start, ref end, _) => {    // base[start..end]
 437                 let args = match (start, end) {
 438                     (&Some(ref e1), &Some(ref e2)) => vec![&**e1, &**e2],
 439                     (&Some(ref e), &None) => vec![&**e],
 440                     (&None, &Some(ref e)) => vec![&**e],
 441                     (&None, &None) => Vec::new()
 442                 };
 443                 let overloaded = self.walk_overloaded_operator(expr, &**base, args);
 444                 assert!(overloaded);
 445             }
 446
 447             ast::ExprCall(ref callee, ref args) => {    // callee(args)
 448                 self.walk_callee(expr, &**callee);
 449                 self.consume_exprs(args);
 450             }
 451
 452             ast::ExprMethodCall(_, _, ref args) => { // callee.m(args)
 453                 self.consume_exprs(args);
 454             }
 455
 456             ast::ExprStruct(_, ref fields, ref opt_with) => {
 457                 self.walk_struct_expr(expr, fields, opt_with);
 458             }
 459
 460             ast::ExprTup(ref exprs) => {
 461                 self.consume_exprs(exprs);
 462             }
 463
 464             ast::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
 465                 self.consume_expr(&**cond_expr);
 466                 self.walk_block(&**then_blk);
 467                 for else_expr in opt_else_expr.iter() {
 468                     self.consume_expr(&**else_expr);
 469                 }
 470             }
 471
 472             ast::ExprIfLet(..) => {
 473                 self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
 474             }
 475
 476             ast::ExprMatch(ref discr, ref arms, _) => {
 477                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
 478                 self.borrow_expr(&**discr, ty::ReEmpty, ty::ImmBorrow, MatchDiscriminant);
 479
 480                 // treatment of the discriminant is handled while walking the arms.
 481                 for arm in arms.iter() {
 482                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 483                     let mode = mode.match_mode();
 484                     self.walk_arm(discr_cmt.clone(), arm, mode);
 485                 }
 486             }
 487
 488             ast::ExprVec(ref exprs) => {
 489                 self.consume_exprs(exprs);
 490             }
 491
 492             ast::ExprAddrOf(m, ref base) => {   // &base
 493                 // make sure that the thing we are pointing out stays valid
 494                 // for the lifetime `scope_r` of the resulting ptr:
 495                 let expr_ty = ty::expr_ty(self.tcx(), expr);
 496                 let r = ty::ty_region(self.tcx(), expr.span, expr_ty);
 497                 let bk = ty::BorrowKind::from_mutbl(m);
 498                 self.borrow_expr(&**base, r, bk, AddrOf);
 499             }
 500
 501             ast::ExprInlineAsm(ref ia) => {
 502                 for &(_, ref input) in ia.inputs.iter() {
 503                     self.consume_expr(&**input);
 504                 }
 505
 506                 for &(_, ref output, is_rw) in ia.outputs.iter() {
 507                     self.mutate_expr(expr, &**output,
 508                                            if is_rw { WriteAndRead } else { JustWrite });
 509                 }
 510             }
 511
 512             ast::ExprBreak(..) |
 513             ast::ExprAgain(..) |
 514             ast::ExprLit(..) => {}
 515
 516             ast::ExprLoop(ref blk, _) => {
 517                 self.walk_block(&**blk);
 518             }
 519
 520             ast::ExprWhile(ref cond_expr, ref blk, _) => {
 521                 self.consume_expr(&**cond_expr);
 522                 self.walk_block(&**blk);
 523             }
 524
 525             ast::ExprWhileLet(..) => {
 526                 self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet");
 527             }
 528
 529             ast::ExprForLoop(ref pat, ref head, ref blk, _) => {
 530                 // The pattern lives as long as the block.
 531                 debug!("walk_expr for loop case: blk id={}", blk.id);
 532                 self.consume_expr(&**head);
 533
 534                 // Fetch the type of the value that the iteration yields to
 535                 // produce the pattern's categorized mutable type.
 536                 let pattern_type = return_if_err!(self.typer.node_ty(pat.id));
 537                 let blk_scope = region::CodeExtent::from_node_id(blk.id);
 538                 let pat_cmt = self.mc.cat_rvalue(pat.id,
 539                                                  pat.span,
 540                                                  ty::ReScope(blk_scope),
 541                                                  pattern_type);
 542                 self.walk_irrefutable_pat(pat_cmt, &**pat);
 543
 544                 self.walk_block(&**blk);
 545             }
 546
 547             ast::ExprUnary(_, ref lhs) => {
 548                 if !self.walk_overloaded_operator(expr, &**lhs, Vec::new()) {
 549                     self.consume_expr(&**lhs);
 550                 }
 551             }
 552
 553             ast::ExprBinary(_, ref lhs, ref rhs) => {
 554                 if !self.walk_overloaded_operator(expr, &**lhs, vec![&**rhs]) {
 555                     self.consume_expr(&**lhs);
 556                     self.consume_expr(&**rhs);
 557                 }
 558             }
 559
 560             ast::ExprBlock(ref blk) => {
 561                 self.walk_block(&**blk);
 562             }
 563
 564             ast::ExprRet(ref opt_expr) => {
 565                 for expr in opt_expr.iter() {
 566                     self.consume_expr(&**expr);
 567                 }
 568             }
 569
 570             ast::ExprAssign(ref lhs, ref rhs) => {
 571                 self.mutate_expr(expr, &**lhs, JustWrite);
 572                 self.consume_expr(&**rhs);
 573             }
 574
 575             ast::ExprCast(ref base, _) => {
 576                 self.consume_expr(&**base);
 577             }
 578
 579             ast::ExprAssignOp(_, ref lhs, ref rhs) => {
 580                 // This will have to change if/when we support
 581                 // overloaded operators for `+=` and so forth.
 582                 self.mutate_expr(expr, &**lhs, WriteAndRead);
 583                 self.consume_expr(&**rhs);
 584             }
 585
 586             ast::ExprRepeat(ref base, ref count) => {
 587                 self.consume_expr(&**base);
 588                 self.consume_expr(&**count);
 589             }
 590
 591             ast::ExprClosure(..) |
 592             ast::ExprProc(..) => {
 593                 self.walk_captures(expr)
 594             }
 595
 596             ast::ExprBox(ref place, ref base) => {
 597                 self.consume_expr(&**place);
 598                 self.consume_expr(&**base);
 599             }
 600
 601             ast::ExprMac(..) => {
 602                 self.tcx().sess.span_bug(
 603                     expr.span,
 604                     "macro expression remains after expansion");
 605             }
 606         }
 607     }
 608
 609     fn walk_callee(&mut self, call: &ast::Expr, callee: &ast::Expr) {
 610         let callee_ty = ty::expr_ty_adjusted(self.tcx(), callee);
 611         debug!("walk_callee: callee={} callee_ty={}",
 612                callee.repr(self.tcx()), callee_ty.repr(self.tcx()));
 613         let call_scope = region::CodeExtent::from_node_id(call.id);
 614         match callee_ty.sty {
 615             ty::ty_bare_fn(..) => {
 616                 self.consume_expr(callee);
 617             }
 618             ty::ty_closure(ref f) => {
 619                 match f.onceness {
 620                     ast::Many => {
 621                         self.borrow_expr(callee,
 622                                          ty::ReScope(call_scope),
 623                                          ty::UniqueImmBorrow,
 624                                          ClosureInvocation);
 625                     }
 626                     ast::Once => {
 627                         self.consume_expr(callee);
 628                     }
 629                 }
 630             }
 631             _ => {
 632                 let overloaded_call_type =
 633                     match self.tcx()
 634                               .method_map
 635                               .borrow()
 636                               .get(&MethodCall::expr(call.id)) {
 637                     Some(ref method_callee) => {
 638                         OverloadedCallType::from_method_origin(
 639                             self.tcx(),
 640                             &method_callee.origin)
 641                     }
 642                     None => {
 643                         self.tcx().sess.span_bug(
 644                             callee.span,
 645                             format!("unexpected callee type {}",
 646                                     callee_ty.repr(self.tcx())).as_slice())
 647                     }
 648                 };
 649                 match overloaded_call_type {
 650                     FnMutOverloadedCall => {
 651                         self.borrow_expr(callee,
 652                                          ty::ReScope(call_scope),
 653                                          ty::MutBorrow,
 654                                          ClosureInvocation);
 655                     }
 656                     FnOverloadedCall => {
 657                         self.borrow_expr(callee,
 658                                          ty::ReScope(call_scope),
 659                                          ty::ImmBorrow,
 660                                          ClosureInvocation);
 661                     }
 662                     FnOnceOverloadedCall => self.consume_expr(callee),
 663                 }
 664             }
 665         }
 666     }
 667
 668     fn walk_stmt(&mut self, stmt: &ast::Stmt) {
 669         match stmt.node {
 670             ast::StmtDecl(ref decl, _) => {
 671                 match decl.node {
 672                     ast::DeclLocal(ref local) => {
 673                         self.walk_local(&**local);
 674                     }
 675
 676                     ast::DeclItem(_) => {
 677                         // we don't visit nested items in this visitor,
 678                         // only the fn body we were given.
 679                     }
 680                 }
 681             }
 682
 683             ast::StmtExpr(ref expr, _) |
 684             ast::StmtSemi(ref expr, _) => {
 685                 self.consume_expr(&**expr);
 686             }
 687
 688             ast::StmtMac(..) => {
 689                 self.tcx().sess.span_bug(stmt.span, "unexpanded stmt macro");
 690             }
 691         }
 692     }
 693
 694     fn walk_local(&mut self, local: &ast::Local) {
 695         match local.init {
 696             None => {
 697                 let delegate = &mut self.delegate;
 698                 pat_util::pat_bindings(&self.typer.tcx().def_map, &*local.pat,
 699                                        |_, id, span, _| {
 700                     delegate.decl_without_init(id, span);
 701                 })
 702             }
 703
 704             Some(ref expr) => {
 705                 // Variable declarations with
 706                 // initializers are considered
 707                 // "assigns", which is handled by
 708                 // `walk_pat`:
 709                 self.walk_expr(&**expr);
 710                 let init_cmt = return_if_err!(self.mc.cat_expr(&**expr));
 711                 self.walk_irrefutable_pat(init_cmt, &*local.pat);
 712             }
 713         }
 714     }
 715
 716     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 717     /// depending on its type.
 718     fn walk_block(&mut self, blk: &ast::Block) {
 719         debug!("walk_block(blk.id={})", blk.id);
 720
 721         for stmt in blk.stmts.iter() {
 722             self.walk_stmt(&**stmt);
 723         }
 724
 725         for tail_expr in blk.expr.iter() {
 726             self.consume_expr(&**tail_expr);
 727         }
 728     }
 729
 730     fn walk_struct_expr(&mut self,
 731                         _expr: &ast::Expr,
 732                         fields: &Vec<ast::Field>,
 733                         opt_with: &Option<P<ast::Expr>>) {
 734         // Consume the expressions supplying values for each field.
 735         for field in fields.iter() {
 736             self.consume_expr(&*field.expr);
 737         }
 738
 739         let with_expr = match *opt_with {
 740             Some(ref w) => &**w,
 741             None => { return; }
 742         };
 743
 744         let with_cmt = return_if_err!(self.mc.cat_expr(&*with_expr));
 745
 746         // Select just those fields of the `with`
 747         // expression that will actually be used
 748         let with_fields = match with_cmt.ty.sty {
 749             ty::ty_struct(did, ref substs) => {
 750                 ty::struct_fields(self.tcx(), did, substs)
 751             }
 752             _ => {
 753                 self.tcx().sess.span_bug(
 754                     with_expr.span,
 755                     "with expression doesn't evaluate to a struct");
 756             }
 757         };
 758
 759         // Consume those fields of the with expression that are needed.
 760         for with_field in with_fields.iter() {
 761             if !contains_field_named(with_field, fields) {
 762                 let cmt_field = self.mc.cat_field(&*with_expr,
 763                                                   with_cmt.clone(),
 764                                                   with_field.name,
 765                                                   with_field.mt.ty);
 766                 self.delegate_consume(with_expr.id, with_expr.span, cmt_field);
 767             }
 768         }
 769
 770         // walk the with expression so that complex expressions
 771         // are properly handled.
 772         self.walk_expr(with_expr);
 773
 774         fn contains_field_named(field: &ty::field,
 775                                 fields: &Vec<ast::Field>)
 776                                 -> bool
 777         {
 778             fields.iter().any(
 779                 |f| f.ident.node.name == field.name)
 780         }
 781     }
 782
 783     // Invoke the appropriate delegate calls for anything that gets
 784     // consumed or borrowed as part of the automatic adjustment
 785     // process.
 786     fn walk_adjustment(&mut self, expr: &ast::Expr) {
 787         let typer = self.typer;
 788         match typer.adjustments().borrow().get(&expr.id) {
 789             None => { }
 790             Some(adjustment) => {
 791                 match *adjustment {
 792                     ty::AdjustAddEnv(..) => {
 793                         // Creating a closure consumes the input and stores it
 794                         // into the resulting rvalue.
 795                         debug!("walk_adjustment(AutoAddEnv)");
 796                         let cmt_unadjusted =
 797                             return_if_err!(self.mc.cat_expr_unadjusted(expr));
 798                         self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 799                     }
 800                     ty::AdjustDerefRef(ty::AutoDerefRef {
 801                         autoref: ref opt_autoref,
 802                         autoderefs: n
 803                     }) => {
 804                         self.walk_autoderefs(expr, n);
 805
 806                         match *opt_autoref {
 807                             None => { }
 808                             Some(ref r) => {
 809                                 self.walk_autoref(expr, r, n);
 810                             }
 811                         }
 812                     }
 813                 }
 814             }
 815         }
 816     }
 817
 818     /// Autoderefs for overloaded Deref calls in fact reference their receiver. That is, if we have
 819     /// `(*x)` where `x` is of type `Rc<T>`, then this in fact is equivalent to `x.deref()`. Since
 820     /// `deref()` is declared with `&self`, this is an autoref of `x`.
 821     fn walk_autoderefs(&mut self,
 822                        expr: &ast::Expr,
 823                        autoderefs: uint) {
 824         debug!("walk_autoderefs expr={} autoderefs={}", expr.repr(self.tcx()), autoderefs);
 825
 826         for i in range(0, autoderefs) {
 827             let deref_id = ty::MethodCall::autoderef(expr.id, i);
 828             match self.typer.node_method_ty(deref_id) {
 829                 None => {}
 830                 Some(method_ty) => {
 831                     let cmt = return_if_err!(self.mc.cat_expr_autoderefd(expr, i));
 832                     let self_ty = ty::ty_fn_args(method_ty)[0];
 833                     let (m, r) = match self_ty.sty {
 834                         ty::ty_rptr(r, ref m) => (m.mutbl, r),
 835                         _ => self.tcx().sess.span_bug(expr.span,
 836                                 format!("bad overloaded deref type {}",
 837                                     method_ty.repr(self.tcx())).as_slice())
 838                     };
 839                     let bk = ty::BorrowKind::from_mutbl(m);
 840                     self.delegate.borrow(expr.id, expr.span, cmt,
 841                                          r, bk, AutoRef);
 842                 }
 843             }
 844         }
 845     }
 846
 847     fn walk_autoref(&mut self,
 848                     expr: &ast::Expr,
 849                     autoref: &ty::AutoRef,
 850                     n: uint) {
 851         debug!("walk_autoref expr={}", expr.repr(self.tcx()));
 852
 853         // Match for unique trait coercions first, since we don't need the
 854         // call to cat_expr_autoderefd.
 855         match *autoref {
 856             ty::AutoUnsizeUniq(ty::UnsizeVtable(..)) |
 857             ty::AutoUnsize(ty::UnsizeVtable(..)) => {
 858                 assert!(n == 1, format!("Expected exactly 1 deref with Uniq \
 859                                          AutoRefs, found: {}", n));
 860                 let cmt_unadjusted =
 861                     return_if_err!(self.mc.cat_expr_unadjusted(expr));
 862                 self.delegate_consume(expr.id, expr.span, cmt_unadjusted);
 863                 return;
 864             }
 865             _ => {}
 866         }
 867
 868         let cmt_derefd = return_if_err!(
 869             self.mc.cat_expr_autoderefd(expr, n));
 870         debug!("walk_adjustment: cmt_derefd={}",
 871                cmt_derefd.repr(self.tcx()));
 872
 873         match *autoref {
 874             ty::AutoPtr(r, m, _) => {
 875                 self.delegate.borrow(expr.id,
 876                                      expr.span,
 877                                      cmt_derefd,
 878                                      r,
 879                                      ty::BorrowKind::from_mutbl(m),
 880                                      AutoRef);
 881             }
 882             ty::AutoUnsizeUniq(_) | ty::AutoUnsize(_) | ty::AutoUnsafe(..) => {}
 883         }
 884     }
 885
 886     fn walk_overloaded_operator(&mut self,
 887                                 expr: &ast::Expr,
 888                                 receiver: &ast::Expr,
 889                                 rhs: Vec<&ast::Expr>)
 890                                 -> bool
 891     {
 892         if !self.typer.is_method_call(expr.id) {
 893             return false;
 894         }
 895
 896         self.walk_expr(receiver);
 897
 898         // Arguments (but not receivers) to overloaded operator
 899         // methods are implicitly autoref'd which sadly does not use
 900         // adjustments, so we must hardcode the borrow here.
 901
 902         let r = ty::ReScope(region::CodeExtent::from_node_id(expr.id));
 903         let bk = ty::ImmBorrow;
 904
 905         for &arg in rhs.iter() {
 906             self.borrow_expr(arg, r, bk, OverloadedOperator);
 907         }
 908         return true;
 909     }
 910
 911     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm) -> TrackMatchMode<Span> {
 912         let mut mode = Unknown;
 913         for pat in arm.pats.iter() {
 914             self.determine_pat_move_mode(discr_cmt.clone(), &**pat, &mut mode);
 915         }
 916         mode
 917     }
 918
 919     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &ast::Arm, mode: MatchMode) {
 920         for pat in arm.pats.iter() {
 921             self.walk_pat(discr_cmt.clone(), &**pat, mode);
 922         }
 923
 924         for guard in arm.guard.iter() {
 925             self.consume_expr(&**guard);
 926         }
 927
 928         self.consume_expr(&*arm.body);
 929     }
 930
 931     /// Walks an pat that occurs in isolation (i.e. top-level of fn
 932     /// arg or let binding.  *Not* a match arm or nested pat.)
 933     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &ast::Pat) {
 934         let mut mode = Unknown;
 935         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 936         let mode = mode.match_mode();
 937         self.walk_pat(cmt_discr, pat, mode);
 938     }
 939
 940     /// Identifies any bindings within `pat` and accumulates within
 941     /// `mode` whether the overall pattern/match structure is a move,
 942     /// copy, or borrow.
 943     fn determine_pat_move_mode(&mut self,
 944                                cmt_discr: mc::cmt<'tcx>,
 945                                pat: &ast::Pat,
 946                                mode: &mut TrackMatchMode<Span>) {
 947         debug!("determine_pat_move_mode cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
 948                pat.repr(self.tcx()));
 949         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |_mc, cmt_pat, pat| {
 950             let tcx = self.typer.tcx();
 951             let def_map = &self.typer.tcx().def_map;
 952             if pat_util::pat_is_binding(def_map, pat) {
 953                 match pat.node {
 954                     ast::PatIdent(ast::BindByRef(_), _, _) =>
 955                         mode.lub(BorrowingMatch),
 956                     ast::PatIdent(ast::BindByValue(_), _, _) => {
 957                         match copy_or_move(tcx, cmt_pat.ty, PatBindingMove) {
 958                             Copy => mode.lub(CopyingMatch),
 959                             Move(_) => mode.lub(MovingMatch),
 960                         }
 961                     }
 962                     _ => {
 963                         tcx.sess.span_bug(
 964                             pat.span,
 965                             "binding pattern not an identifier");
 966                     }
 967                 }
 968             }
 969         }));
 970     }
 971
 972     /// The core driver for walking a pattern; `match_mode` must be
 973     /// established up front, e.g. via `determine_pat_move_mode` (see
 974     /// also `walk_irrefutable_pat` for patterns that stand alone).
 975     fn walk_pat(&mut self,
 976                 cmt_discr: mc::cmt<'tcx>,
 977                 pat: &ast::Pat,
 978                 match_mode: MatchMode) {
 979         debug!("walk_pat cmt_discr={} pat={}", cmt_discr.repr(self.tcx()),
 980                pat.repr(self.tcx()));
 981
 982         let mc = &self.mc;
 983         let typer = self.typer;
 984         let tcx = typer.tcx();
 985         let def_map = &self.typer.tcx().def_map;
 986         let delegate = &mut self.delegate;
 987
 988         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |mc, cmt_pat, pat| {
 989             if pat_util::pat_is_binding(def_map, pat) {
 990                 let tcx = typer.tcx();
 991
 992                 debug!("binding cmt_pat={} pat={} match_mode={}",
 993                        cmt_pat.repr(tcx),
 994                        pat.repr(tcx),
 995                        match_mode);
 996
 997                 // pat_ty: the type of the binding being produced.
 998                 let pat_ty = return_if_err!(typer.node_ty(pat.id));
 999
1000                 // Each match binding is effectively an assignment to the
1001                 // binding being produced.
1002                 let def = def_map.borrow()[pat.id].clone();
1003                 match mc.cat_def(pat.id, pat.span, pat_ty, def) {
1004                     Ok(binding_cmt) => {
1005                         delegate.mutate(pat.id, pat.span, binding_cmt, Init);
1006                     }
1007                     Err(_) => { }
1008                 }
1009
1010                 // It is also a borrow or copy/move of the value being matched.
1011                 match pat.node {
1012                     ast::PatIdent(ast::BindByRef(m), _, _) => {
1013                         let (r, bk) = {
1014                             (ty::ty_region(tcx, pat.span, pat_ty),
1015                              ty::BorrowKind::from_mutbl(m))
1016                         };
1017                         delegate.borrow(pat.id, pat.span, cmt_pat,
1018                                              r, bk, RefBinding);
1019                     }
1020                     ast::PatIdent(ast::BindByValue(_), _, _) => {
1021                         let mode = copy_or_move(typer.tcx(), cmt_pat.ty, PatBindingMove);
1022                         debug!("walk_pat binding consuming pat");
1023                         delegate.consume_pat(pat, cmt_pat, mode);
1024                     }
1025                     _ => {
1026                         typer.tcx().sess.span_bug(
1027                             pat.span,
1028                             "binding pattern not an identifier");
1029                     }
1030                 }
1031             } else {
1032                 match pat.node {
1033                     ast::PatVec(_, Some(ref slice_pat), _) => {
1034                         // The `slice_pat` here creates a slice into
1035                         // the original vector.  This is effectively a
1036                         // borrow of the elements of the vector being
1037                         // matched.
1038
1039                         let (slice_cmt, slice_mutbl, slice_r) = {
1040                             match mc.cat_slice_pattern(cmt_pat, &**slice_pat) {
1041                                 Ok(v) => v,
1042                                 Err(()) => {
1043                                     tcx.sess.span_bug(slice_pat.span,
1044                                                       "Err from mc")
1045                                 }
1046                             }
1047                         };
1048
1049                         // Note: We declare here that the borrow
1050                         // occurs upon entering the `[...]`
1051                         // pattern. This implies that something like
1052                         // `[a, ..b]` where `a` is a move is illegal,
1053                         // because the borrow is already in effect.
1054                         // In fact such a move would be safe-ish, but
1055                         // it effectively *requires* that we use the
1056                         // nulling out semantics to indicate when a
1057                         // value has been moved, which we are trying
1058                         // to move away from.  Otherwise, how can we
1059                         // indicate that the first element in the
1060                         // vector has been moved?  Eventually, we
1061                         // could perhaps modify this rule to permit
1062                         // `[..a, b]` where `b` is a move, because in
1063                         // that case we can adjust the length of the
1064                         // original vec accordingly, but we'd have to
1065                         // make trans do the right thing, and it would
1066                         // only work for `~` vectors. It seems simpler
1067                         // to just require that people call
1068                         // `vec.pop()` or `vec.unshift()`.
1069                         let slice_bk = ty::BorrowKind::from_mutbl(slice_mutbl);
1070                         delegate.borrow(pat.id, pat.span,
1071                                         slice_cmt, slice_r,
1072                                         slice_bk, RefBinding);
1073                     }
1074                     _ => { }
1075                 }
1076             }
1077         }));
1078
1079         // Do a second pass over the pattern, calling `matched_pat` on
1080         // the interior nodes (enum variants and structs), as opposed
1081         // to the above loop's visit of than the bindings that form
1082         // the leaves of the pattern tree structure.
1083         return_if_err!(mc.cat_pattern(cmt_discr, pat, |mc, cmt_pat, pat| {
1084             let def_map = def_map.borrow();
1085             let tcx = typer.tcx();
1086
1087             match pat.node {
1088                 ast::PatEnum(_, _) | ast::PatIdent(_, _, None) | ast::PatStruct(..) => {
1089                     match def_map.get(&pat.id) {
1090                         None => {
1091                             // no definition found: pat is not a
1092                             // struct or enum pattern.
1093                         }
1094
1095                         Some(&def::DefVariant(enum_did, variant_did, _is_struct)) => {
1096                             let downcast_cmt =
1097                                 if ty::enum_is_univariant(tcx, enum_did) {
1098                                     cmt_pat
1099                                 } else {
1100                                     let cmt_pat_ty = cmt_pat.ty;
1101                                     mc.cat_downcast(pat, cmt_pat, cmt_pat_ty, variant_did)
1102                                 };
1103
1104                             debug!("variant downcast_cmt={} pat={}",
1105                                    downcast_cmt.repr(tcx),
1106                                    pat.repr(tcx));
1107
1108                             delegate.matched_pat(pat, downcast_cmt, match_mode);
1109                         }
1110
1111                         Some(&def::DefStruct(..)) | Some(&def::DefTy(_, false)) => {
1112                             // A struct (in either the value or type
1113                             // namespace; we encounter the former on
1114                             // e.g. patterns for unit structs).
1115
1116                             debug!("struct cmt_pat={} pat={}",
1117                                    cmt_pat.repr(tcx),
1118                                    pat.repr(tcx));
1119
1120                             delegate.matched_pat(pat, cmt_pat, match_mode);
1121                         }
1122
1123                         Some(&def::DefConst(..)) |
1124                         Some(&def::DefLocal(..)) => {
1125                             // This is a leaf (i.e. identifier binding
1126                             // or constant value to match); thus no
1127                             // `matched_pat` call.
1128                         }
1129
1130                         Some(def @ &def::DefTy(_, true)) => {
1131                             // An enum's type -- should never be in a
1132                             // pattern.
1133
1134                             let msg = format!("Pattern has unexpected type: {}", def);
1135                             tcx.sess.span_bug(pat.span, msg.as_slice())
1136                         }
1137
1138                         Some(def) => {
1139                             // Remaining cases are e.g. DefFn, to
1140                             // which identifiers within patterns
1141                             // should not resolve.
1142
1143                             let msg = format!("Pattern has unexpected def: {}", def);
1144                             tcx.sess.span_bug(pat.span, msg.as_slice())
1145                         }
1146                     }
1147                 }
1148
1149                 ast::PatIdent(_, _, Some(_)) => {
1150                     // Do nothing; this is a binding (not a enum
1151                     // variant or struct), and the cat_pattern call
1152                     // will visit the substructure recursively.
1153                 }
1154
1155                 ast::PatWild(_) | ast::PatTup(..) | ast::PatBox(..) |
1156                 ast::PatRegion(..) | ast::PatLit(..) | ast::PatRange(..) |
1157                 ast::PatVec(..) | ast::PatMac(..) => {
1158                     // Similarly, each of these cases does not
1159                     // correspond to a enum variant or struct, so we
1160                     // do not do any `matched_pat` calls for these
1161                     // cases either.
1162                 }
1163             }
1164         }));
1165     }
1166
1167     fn walk_captures(&mut self, closure_expr: &ast::Expr) {
1168         debug!("walk_captures({})", closure_expr.repr(self.tcx()));
1169
1170         let tcx = self.typer.tcx();
1171         ty::with_freevars(tcx, closure_expr.id, |freevars| {
1172             match self.tcx().capture_mode(closure_expr.id) {
1173                 ast::CaptureByRef => {
1174                     self.walk_by_ref_captures(closure_expr, freevars);
1175                 }
1176                 ast::CaptureByValue => {
1177                     self.walk_by_value_captures(closure_expr, freevars);
1178                 }
1179             }
1180         });
1181     }
1182
1183     fn walk_by_ref_captures(&mut self,
1184                             closure_expr: &ast::Expr,
1185                             freevars: &[ty::Freevar]) {
1186         for freevar in freevars.iter() {
1187             let id_var = freevar.def.def_id().node;
1188             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1189                                                                closure_expr.span,
1190                                                                freevar.def));
1191
1192             // Lookup the kind of borrow the callee requires, as
1193             // inferred by regionbk
1194             let upvar_id = ty::UpvarId { var_id: id_var,
1195                                          closure_expr_id: closure_expr.id };
1196             let upvar_borrow = self.tcx().upvar_borrow_map.borrow()[upvar_id].clone();
1197
1198             self.delegate.borrow(closure_expr.id,
1199                                  closure_expr.span,
1200                                  cmt_var,
1201                                  upvar_borrow.region,
1202                                  upvar_borrow.kind,
1203                                  ClosureCapture(freevar.span));
1204         }
1205     }
1206
1207     fn walk_by_value_captures(&mut self,
1208                               closure_expr: &ast::Expr,
1209                               freevars: &[ty::Freevar]) {
1210         for freevar in freevars.iter() {
1211             let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.id,
1212                                                                closure_expr.span,
1213                                                                freevar.def));
1214             let mode = copy_or_move(self.tcx(), cmt_var.ty, CaptureMove);
1215             self.delegate.consume(closure_expr.id, freevar.span, cmt_var, mode);
1216         }
1217     }
1218
1219     fn cat_captured_var(&mut self,
1220                         closure_id: ast::NodeId,
1221                         closure_span: Span,
1222                         upvar_def: def::Def)
1223                         -> mc::McResult<mc::cmt<'tcx>> {
1224         // Create the cmt for the variable being borrowed, from the
1225         // caller's perspective
1226         let var_id = upvar_def.def_id().node;
1227         let var_ty = try!(self.typer.node_ty(var_id));
1228         self.mc.cat_def(closure_id, closure_span, var_ty, upvar_def)
1229     }
1230 }
1231
1232 fn copy_or_move<'tcx>(tcx: &ty::ctxt<'tcx>, ty: Ty<'tcx>,
1233                       move_reason: MoveReason) -> ConsumeMode {
1234     if ty::type_moves_by_default(tcx, ty) { Move(move_reason) } else { Copy }
1235 }
1236