src/librustc/middle/expr_use_visitor.rs

   1 //! A different sort of visitor for walking fn bodies. Unlike the
   2 //! normal visitor, which just walks the entire body in one shot, the
   3 //! `ExprUseVisitor` determines how expressions are being used.
   4
   5 pub use self::LoanCause::*;
   6 pub use self::ConsumeMode::*;
   7 pub use self::MoveReason::*;
   8 pub use self::MatchMode::*;
   9 use self::TrackMatchMode::*;
  10 use self::OverloadedCallType::*;
  11
  12 use crate::hir::def::{CtorOf, Res, DefKind};
  13 use crate::hir::def_id::DefId;
  14 use crate::infer::InferCtxt;
  15 use crate::middle::mem_categorization as mc;
  16 use crate::middle::region;
  17 use crate::ty::{self, DefIdTree, TyCtxt, adjustment};
  18
  19 use crate::hir::{self, PatKind};
  20 use std::rc::Rc;
  21 use syntax::ptr::P;
  22 use syntax_pos::Span;
  23 use crate::util::nodemap::ItemLocalSet;
  24
  25 ///////////////////////////////////////////////////////////////////////////
  26 // The Delegate trait
  27
  28 /// This trait defines the callbacks you can expect to receive when
  29 /// employing the ExprUseVisitor.
  30 pub trait Delegate<'tcx> {
  31     // The value found at `cmt` is either copied or moved, depending
  32     // on mode.
  33     fn consume(&mut self,
  34                consume_id: hir::HirId,
  35                consume_span: Span,
  36                cmt: &mc::cmt_<'tcx>,
  37                mode: ConsumeMode);
  38
  39     // The value found at `cmt` has been determined to match the
  40     // pattern binding `matched_pat`, and its subparts are being
  41     // copied or moved depending on `mode`.  Note that `matched_pat`
  42     // is called on all variant/structs in the pattern (i.e., the
  43     // interior nodes of the pattern's tree structure) while
  44     // consume_pat is called on the binding identifiers in the pattern
  45     // (which are leaves of the pattern's tree structure).
  46     //
  47     // Note that variants/structs and identifiers are disjoint; thus
  48     // `matched_pat` and `consume_pat` are never both called on the
  49     // same input pattern structure (though of `consume_pat` can be
  50     // called on a subpart of an input passed to `matched_pat).
  51     fn matched_pat(&mut self,
  52                    matched_pat: &hir::Pat,
  53                    cmt: &mc::cmt_<'tcx>,
  54                    mode: MatchMode);
  55
  56     // The value found at `cmt` is either copied or moved via the
  57     // pattern binding `consume_pat`, depending on mode.
  58     fn consume_pat(&mut self,
  59                    consume_pat: &hir::Pat,
  60                    cmt: &mc::cmt_<'tcx>,
  61                    mode: ConsumeMode);
  62
  63     // The value found at `borrow` is being borrowed at the point
  64     // `borrow_id` for the region `loan_region` with kind `bk`.
  65     fn borrow(&mut self,
  66               borrow_id: hir::HirId,
  67               borrow_span: Span,
  68               cmt: &mc::cmt_<'tcx>,
  69               loan_region: ty::Region<'tcx>,
  70               bk: ty::BorrowKind,
  71               loan_cause: LoanCause);
  72
  73     // The local variable `id` is declared but not initialized.
  74     fn decl_without_init(&mut self,
  75                          id: hir::HirId,
  76                          span: Span);
  77
  78     // The path at `cmt` is being assigned to.
  79     fn mutate(&mut self,
  80               assignment_id: hir::HirId,
  81               assignment_span: Span,
  82               assignee_cmt: &mc::cmt_<'tcx>,
  83               mode: MutateMode);
  84
  85     // A nested closure or generator - only one layer deep.
  86     fn nested_body(&mut self, _body_id: hir::BodyId) {}
  87 }
  88
  89 #[derive(Copy, Clone, PartialEq, Debug)]
  90 pub enum LoanCause {
  91     ClosureCapture(Span),
  92     AddrOf,
  93     AutoRef,
  94     AutoUnsafe,
  95     RefBinding,
  96     OverloadedOperator,
  97     ClosureInvocation,
  98     ForLoop,
  99     MatchDiscriminant
 100 }
 101
 102 #[derive(Copy, Clone, PartialEq, Debug)]
 103 pub enum ConsumeMode {
 104     Copy,                // reference to x where x has a type that copies
 105     Move(MoveReason),    // reference to x where x has a type that moves
 106 }
 107
 108 #[derive(Copy, Clone, PartialEq, Debug)]
 109 pub enum MoveReason {
 110     DirectRefMove,
 111     PatBindingMove,
 112     CaptureMove,
 113 }
 114
 115 #[derive(Copy, Clone, PartialEq, Debug)]
 116 pub enum MatchMode {
 117     NonBindingMatch,
 118     BorrowingMatch,
 119     CopyingMatch,
 120     MovingMatch,
 121 }
 122
 123 #[derive(Copy, Clone, PartialEq, Debug)]
 124 enum TrackMatchMode {
 125     Unknown,
 126     Definite(MatchMode),
 127     Conflicting,
 128 }
 129
 130 impl TrackMatchMode {
 131     // Builds up the whole match mode for a pattern from its constituent
 132     // parts.  The lattice looks like this:
 133     //
 134     //          Conflicting
 135     //            /     \
 136     //           /       \
 137     //      Borrowing   Moving
 138     //           \       /
 139     //            \     /
 140     //            Copying
 141     //               |
 142     //          NonBinding
 143     //               |
 144     //            Unknown
 145     //
 146     // examples:
 147     //
 148     // * `(_, some_int)` pattern is Copying, since
 149     //   NonBinding + Copying => Copying
 150     //
 151     // * `(some_int, some_box)` pattern is Moving, since
 152     //   Copying + Moving => Moving
 153     //
 154     // * `(ref x, some_box)` pattern is Conflicting, since
 155     //   Borrowing + Moving => Conflicting
 156     //
 157     // Note that the `Unknown` and `Conflicting` states are
 158     // represented separately from the other more interesting
 159     // `Definite` states, which simplifies logic here somewhat.
 160     fn lub(&mut self, mode: MatchMode) {
 161         *self = match (*self, mode) {
 162             // Note that clause order below is very significant.
 163             (Unknown, new) => Definite(new),
 164             (Definite(old), new) if old == new => Definite(old),
 165
 166             (Definite(old), NonBindingMatch) => Definite(old),
 167             (Definite(NonBindingMatch), new) => Definite(new),
 168
 169             (Definite(old), CopyingMatch) => Definite(old),
 170             (Definite(CopyingMatch), new) => Definite(new),
 171
 172             (Definite(_), _) => Conflicting,
 173             (Conflicting, _) => *self,
 174         };
 175     }
 176
 177     fn match_mode(&self) -> MatchMode {
 178         match *self {
 179             Unknown => NonBindingMatch,
 180             Definite(mode) => mode,
 181             Conflicting => {
 182                 // Conservatively return MovingMatch to let the
 183                 // compiler continue to make progress.
 184                 MovingMatch
 185             }
 186         }
 187     }
 188 }
 189
 190 #[derive(Copy, Clone, PartialEq, Debug)]
 191 pub enum MutateMode {
 192     Init,
 193     JustWrite,    // x = y
 194     WriteAndRead, // x += y
 195 }
 196
 197 #[derive(Copy, Clone)]
 198 enum OverloadedCallType {
 199     FnOverloadedCall,
 200     FnMutOverloadedCall,
 201     FnOnceOverloadedCall,
 202 }
 203
 204 impl OverloadedCallType {
 205     fn from_trait_id(tcx: TyCtxt<'_, '_, '_>, trait_id: DefId) -> OverloadedCallType {
 206         for &(maybe_function_trait, overloaded_call_type) in &[
 207             (tcx.lang_items().fn_once_trait(), FnOnceOverloadedCall),
 208             (tcx.lang_items().fn_mut_trait(), FnMutOverloadedCall),
 209             (tcx.lang_items().fn_trait(), FnOverloadedCall)
 210         ] {
 211             match maybe_function_trait {
 212                 Some(function_trait) if function_trait == trait_id => {
 213                     return overloaded_call_type
 214                 }
 215                 _ => continue,
 216             }
 217         }
 218
 219         bug!("overloaded call didn't map to known function trait")
 220     }
 221
 222     fn from_method_id(tcx: TyCtxt<'_, '_, '_>, method_id: DefId) -> OverloadedCallType {
 223         let method = tcx.associated_item(method_id);
 224         OverloadedCallType::from_trait_id(tcx, method.container.id())
 225     }
 226 }
 227
 228 ///////////////////////////////////////////////////////////////////////////
 229 // The ExprUseVisitor type
 230 //
 231 // This is the code that actually walks the tree.
 232 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 233     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 234     delegate: &'a mut dyn Delegate<'tcx>,
 235     param_env: ty::ParamEnv<'tcx>,
 236 }
 237
 238 // If the MC results in an error, it's because the type check
 239 // failed (or will fail, when the error is uncovered and reported
 240 // during writeback). In this case, we just ignore this part of the
 241 // code.
 242 //
 243 // Note that this macro appears similar to try!(), but, unlike try!(),
 244 // it does not propagate the error.
 245 macro_rules! return_if_err {
 246     ($inp: expr) => (
 247         match $inp {
 248             Ok(v) => v,
 249             Err(()) => {
 250                 debug!("mc reported err");
 251                 return
 252             }
 253         }
 254     )
 255 }
 256
 257 impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
 258     /// Creates the ExprUseVisitor, configuring it with the various options provided:
 259     ///
 260     /// - `delegate` -- who receives the callbacks
 261     /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
 262     /// - `region_scope_tree` --- region scope tree for the code being analyzed
 263     /// - `tables` --- typeck results for the code being analyzed
 264     /// - `rvalue_promotable_map` --- if you care about rvalue promotion, then provide
 265     ///   the map here (it can be computed with `tcx.rvalue_promotable_map(def_id)`).
 266     ///   `None` means that rvalues will be given more conservative lifetimes.
 267     ///
 268     /// See also `with_infer`, which is used *during* typeck.
 269     pub fn new(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 270                tcx: TyCtxt<'a, 'tcx, 'tcx>,
 271                param_env: ty::ParamEnv<'tcx>,
 272                region_scope_tree: &'a region::ScopeTree,
 273                tables: &'a ty::TypeckTables<'tcx>,
 274                rvalue_promotable_map: Option<&'tcx ItemLocalSet>)
 275                -> Self
 276     {
 277         ExprUseVisitor {
 278             mc: mc::MemCategorizationContext::new(tcx,
 279                                                   region_scope_tree,
 280                                                   tables,
 281                                                   rvalue_promotable_map),
 282             delegate,
 283             param_env,
 284         }
 285     }
 286 }
 287
 288 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 289     pub fn with_infer(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 290                       infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 291                       param_env: ty::ParamEnv<'tcx>,
 292                       region_scope_tree: &'a region::ScopeTree,
 293                       tables: &'a ty::TypeckTables<'tcx>)
 294                       -> Self
 295     {
 296         ExprUseVisitor {
 297             mc: mc::MemCategorizationContext::with_infer(infcx, region_scope_tree, tables),
 298             delegate,
 299             param_env,
 300         }
 301     }
 302
 303     pub fn consume_body(&mut self, body: &hir::Body) {
 304         debug!("consume_body(body={:?})", body);
 305
 306         for arg in &body.arguments {
 307             let arg_ty = return_if_err!(self.mc.pat_ty_adjusted(&arg.pat));
 308             debug!("consume_body: arg_ty = {:?}", arg_ty);
 309
 310             let fn_body_scope_r =
 311                 self.tcx().mk_region(ty::ReScope(
 312                     region::Scope {
 313                         id: body.value.hir_id.local_id,
 314                         data: region::ScopeData::Node
 315                 }));
 316             let arg_cmt = Rc::new(self.mc.cat_rvalue(
 317                 arg.hir_id,
 318                 arg.pat.span,
 319                 fn_body_scope_r, // Args live only as long as the fn body.
 320                 arg_ty));
 321
 322             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 323         }
 324
 325         self.consume_expr(&body.value);
 326     }
 327
 328     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 329         self.mc.tcx
 330     }
 331
 332     fn delegate_consume(&mut self,
 333                         consume_id: hir::HirId,
 334                         consume_span: Span,
 335                         cmt: &mc::cmt_<'tcx>) {
 336         debug!("delegate_consume(consume_id={}, cmt={:?})",
 337                consume_id, cmt);
 338
 339         let mode = copy_or_move(&self.mc, self.param_env, cmt, DirectRefMove);
 340         self.delegate.consume(consume_id, consume_span, cmt, mode);
 341     }
 342
 343     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 344         for expr in exprs {
 345             self.consume_expr(&expr);
 346         }
 347     }
 348
 349     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 350         debug!("consume_expr(expr={:?})", expr);
 351
 352         let cmt = return_if_err!(self.mc.cat_expr(expr));
 353         self.delegate_consume(expr.hir_id, expr.span, &cmt);
 354         self.walk_expr(expr);
 355     }
 356
 357     fn mutate_expr(&mut self,
 358                    span: Span,
 359                    assignment_expr: &hir::Expr,
 360                    expr: &hir::Expr,
 361                    mode: MutateMode) {
 362         let cmt = return_if_err!(self.mc.cat_expr(expr));
 363         self.delegate.mutate(assignment_expr.hir_id, span, &cmt, mode);
 364         self.walk_expr(expr);
 365     }
 366
 367     fn borrow_expr(&mut self,
 368                    expr: &hir::Expr,
 369                    r: ty::Region<'tcx>,
 370                    bk: ty::BorrowKind,
 371                    cause: LoanCause) {
 372         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 373                expr, r, bk);
 374
 375         let cmt = return_if_err!(self.mc.cat_expr(expr));
 376         self.delegate.borrow(expr.hir_id, expr.span, &cmt, r, bk, cause);
 377
 378         self.walk_expr(expr)
 379     }
 380
 381     fn select_from_expr(&mut self, expr: &hir::Expr) {
 382         self.walk_expr(expr)
 383     }
 384
 385     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 386         debug!("walk_expr(expr={:?})", expr);
 387
 388         self.walk_adjustment(expr);
 389
 390         match expr.node {
 391             hir::ExprKind::Path(_) => { }
 392
 393             hir::ExprKind::Type(ref subexpr, _) => {
 394                 self.walk_expr(&subexpr)
 395             }
 396
 397             hir::ExprKind::Unary(hir::UnDeref, ref base) => { // *base
 398                 self.select_from_expr(&base);
 399             }
 400
 401             hir::ExprKind::Field(ref base, _) => { // base.f
 402                 self.select_from_expr(&base);
 403             }
 404
 405             hir::ExprKind::Index(ref lhs, ref rhs) => { // lhs[rhs]
 406                 self.select_from_expr(&lhs);
 407                 self.consume_expr(&rhs);
 408             }
 409
 410             hir::ExprKind::Call(ref callee, ref args) => { // callee(args)
 411                 self.walk_callee(expr, &callee);
 412                 self.consume_exprs(args);
 413             }
 414
 415             hir::ExprKind::MethodCall(.., ref args) => { // callee.m(args)
 416                 self.consume_exprs(args);
 417             }
 418
 419             hir::ExprKind::Struct(_, ref fields, ref opt_with) => {
 420                 self.walk_struct_expr(fields, opt_with);
 421             }
 422
 423             hir::ExprKind::Tup(ref exprs) => {
 424                 self.consume_exprs(exprs);
 425             }
 426
 427             hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 428                 self.consume_expr(&cond_expr);
 429                 self.walk_expr(&then_expr);
 430                 if let Some(ref else_expr) = *opt_else_expr {
 431                     self.consume_expr(&else_expr);
 432                 }
 433             }
 434
 435             hir::ExprKind::Match(ref discr, ref arms, _) => {
 436                 let discr_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&discr)));
 437                 let r = self.tcx().lifetimes.re_empty;
 438                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 439
 440                 // treatment of the discriminant is handled while walking the arms.
 441                 for arm in arms {
 442                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 443                     let mode = mode.match_mode();
 444                     self.walk_arm(discr_cmt.clone(), arm, mode);
 445                 }
 446             }
 447
 448             hir::ExprKind::Array(ref exprs) => {
 449                 self.consume_exprs(exprs);
 450             }
 451
 452             hir::ExprKind::AddrOf(m, ref base) => {   // &base
 453                 // make sure that the thing we are pointing out stays valid
 454                 // for the lifetime `scope_r` of the resulting ptr:
 455                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 456                 if let ty::Ref(r, _, _) = expr_ty.sty {
 457                     let bk = ty::BorrowKind::from_mutbl(m);
 458                     self.borrow_expr(&base, r, bk, AddrOf);
 459                 }
 460             }
 461
 462             hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
 463                 for (o, output) in ia.outputs.iter().zip(outputs) {
 464                     if o.is_indirect {
 465                         self.consume_expr(output);
 466                     } else {
 467                         self.mutate_expr(
 468                             output.span,
 469                             expr,
 470                             output,
 471                             if o.is_rw {
 472                                 MutateMode::WriteAndRead
 473                             } else {
 474                                 MutateMode::JustWrite
 475                             },
 476                         );
 477                     }
 478                 }
 479                 self.consume_exprs(inputs);
 480             }
 481
 482             hir::ExprKind::Continue(..) |
 483             hir::ExprKind::Lit(..) |
 484             hir::ExprKind::Err => {}
 485
 486             hir::ExprKind::Loop(ref blk, _, _) => {
 487                 self.walk_block(&blk);
 488             }
 489
 490             hir::ExprKind::While(ref cond_expr, ref blk, _) => {
 491                 self.consume_expr(&cond_expr);
 492                 self.walk_block(&blk);
 493             }
 494
 495             hir::ExprKind::Unary(_, ref lhs) => {
 496                 self.consume_expr(&lhs);
 497             }
 498
 499             hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
 500                 self.consume_expr(&lhs);
 501                 self.consume_expr(&rhs);
 502             }
 503
 504             hir::ExprKind::Block(ref blk, _) => {
 505                 self.walk_block(&blk);
 506             }
 507
 508             hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
 509                 if let Some(ref expr) = *opt_expr {
 510                     self.consume_expr(&expr);
 511                 }
 512             }
 513
 514             hir::ExprKind::Assign(ref lhs, ref rhs) => {
 515                 self.mutate_expr(expr.span, expr, &lhs, MutateMode::JustWrite);
 516                 self.consume_expr(&rhs);
 517             }
 518
 519             hir::ExprKind::Cast(ref base, _) => {
 520                 self.consume_expr(&base);
 521             }
 522
 523             hir::ExprKind::DropTemps(ref expr) => {
 524                 self.consume_expr(&expr);
 525             }
 526
 527             hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
 528                 if self.mc.tables.is_method_call(expr) {
 529                     self.consume_expr(lhs);
 530                 } else {
 531                     self.mutate_expr(expr.span, expr, &lhs, MutateMode::WriteAndRead);
 532                 }
 533                 self.consume_expr(&rhs);
 534             }
 535
 536             hir::ExprKind::Repeat(ref base, _) => {
 537                 self.consume_expr(&base);
 538             }
 539
 540             hir::ExprKind::Closure(_, _, body_id, fn_decl_span, _) => {
 541                 self.delegate.nested_body(body_id);
 542                 self.walk_captures(expr, fn_decl_span);
 543             }
 544
 545             hir::ExprKind::Box(ref base) => {
 546                 self.consume_expr(&base);
 547             }
 548
 549             hir::ExprKind::Yield(ref value) => {
 550                 self.consume_expr(&value);
 551             }
 552         }
 553     }
 554
 555     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 556         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 557         debug!("walk_callee: callee={:?} callee_ty={:?}",
 558                callee, callee_ty);
 559         match callee_ty.sty {
 560             ty::FnDef(..) | ty::FnPtr(_) => {
 561                 self.consume_expr(callee);
 562             }
 563             ty::Error => { }
 564             _ => {
 565                 if let Some(def_id) = self.mc.tables.type_dependent_def_id(call.hir_id) {
 566                     let call_scope = region::Scope {
 567                         id: call.hir_id.local_id,
 568                         data: region::ScopeData::Node
 569                     };
 570                     match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 571                         FnMutOverloadedCall => {
 572                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 573                             self.borrow_expr(callee,
 574                                             call_scope_r,
 575                                             ty::MutBorrow,
 576                                             ClosureInvocation);
 577                         }
 578                         FnOverloadedCall => {
 579                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 580                             self.borrow_expr(callee,
 581                                             call_scope_r,
 582                                             ty::ImmBorrow,
 583                                             ClosureInvocation);
 584                         }
 585                         FnOnceOverloadedCall => self.consume_expr(callee),
 586                     }
 587                 } else {
 588                     self.tcx().sess.delay_span_bug(call.span,
 589                                                    "no type-dependent def for overloaded call");
 590                 }
 591             }
 592         }
 593     }
 594
 595     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 596         match stmt.node {
 597             hir::StmtKind::Local(ref local) => {
 598                 self.walk_local(&local);
 599             }
 600
 601             hir::StmtKind::Item(_) => {
 602                 // we don't visit nested items in this visitor,
 603                 // only the fn body we were given.
 604             }
 605
 606             hir::StmtKind::Expr(ref expr) |
 607             hir::StmtKind::Semi(ref expr) => {
 608                 self.consume_expr(&expr);
 609             }
 610         }
 611     }
 612
 613     fn walk_local(&mut self, local: &hir::Local) {
 614         match local.init {
 615             None => {
 616                 local.pat.each_binding(|_, hir_id, span, _| {
 617                     self.delegate.decl_without_init(hir_id, span);
 618                 })
 619             }
 620
 621             Some(ref expr) => {
 622                 // Variable declarations with
 623                 // initializers are considered
 624                 // "assigns", which is handled by
 625                 // `walk_pat`:
 626                 self.walk_expr(&expr);
 627                 let init_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&expr)));
 628                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 629             }
 630         }
 631     }
 632
 633     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 634     /// depending on its type.
 635     fn walk_block(&mut self, blk: &hir::Block) {
 636         debug!("walk_block(blk.hir_id={})", blk.hir_id);
 637
 638         for stmt in &blk.stmts {
 639             self.walk_stmt(stmt);
 640         }
 641
 642         if let Some(ref tail_expr) = blk.expr {
 643             self.consume_expr(&tail_expr);
 644         }
 645     }
 646
 647     fn walk_struct_expr(&mut self,
 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 = Rc::new(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         match with_cmt.ty.sty {
 665             ty::Adt(adt, substs) if adt.is_struct() => {
 666                 // Consume those fields of the with expression that are needed.
 667                 for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() {
 668                     let is_mentioned = fields.iter().any(|f| {
 669                         self.tcx().field_index(f.hir_id, self.mc.tables) == f_index
 670                     });
 671                     if !is_mentioned {
 672                         let cmt_field = self.mc.cat_field(
 673                             &*with_expr,
 674                             with_cmt.clone(),
 675                             f_index,
 676                             with_field.ident,
 677                             with_field.ty(self.tcx(), substs)
 678                         );
 679                         self.delegate_consume(with_expr.hir_id, with_expr.span, &cmt_field);
 680                     }
 681                 }
 682             }
 683             _ => {
 684                 // the base expression should always evaluate to a
 685                 // struct; however, when EUV is run during typeck, it
 686                 // may not. This will generate an error earlier in typeck,
 687                 // so we can just ignore it.
 688                 if !self.tcx().sess.has_errors() {
 689                     span_bug!(
 690                         with_expr.span,
 691                         "with expression doesn't evaluate to a struct");
 692                 }
 693             }
 694         }
 695
 696         // walk the with expression so that complex expressions
 697         // are properly handled.
 698         self.walk_expr(with_expr);
 699     }
 700
 701     // Invoke the appropriate delegate calls for anything that gets
 702     // consumed or borrowed as part of the automatic adjustment
 703     // process.
 704     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 705         let adjustments = self.mc.tables.expr_adjustments(expr);
 706         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 707         for adjustment in adjustments {
 708             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 709             match adjustment.kind {
 710                 adjustment::Adjust::NeverToAny |
 711                 adjustment::Adjust::Pointer(_)  => {
 712                     // Creating a closure/fn-pointer or unsizing consumes
 713                     // the input and stores it into the resulting rvalue.
 714                     self.delegate_consume(expr.hir_id, expr.span, &cmt);
 715                 }
 716
 717                 adjustment::Adjust::Deref(None) => {}
 718
 719                 // Autoderefs for overloaded Deref calls in fact reference
 720                 // their receiver. That is, if we have `(*x)` where `x`
 721                 // is of type `Rc<T>`, then this in fact is equivalent to
 722                 // `x.deref()`. Since `deref()` is declared with `&self`,
 723                 // this is an autoref of `x`.
 724                 adjustment::Adjust::Deref(Some(ref deref)) => {
 725                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 726                     self.delegate.borrow(expr.hir_id, expr.span, &cmt, deref.region, bk, AutoRef);
 727                 }
 728
 729                 adjustment::Adjust::Borrow(ref autoref) => {
 730                     self.walk_autoref(expr, &cmt, autoref);
 731                 }
 732             }
 733             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 734         }
 735     }
 736
 737     /// Walks the autoref `autoref` applied to the autoderef'd
 738     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 739     /// after all relevant autoderefs have occurred.
 740     fn walk_autoref(&mut self,
 741                     expr: &hir::Expr,
 742                     cmt_base: &mc::cmt_<'tcx>,
 743                     autoref: &adjustment::AutoBorrow<'tcx>) {
 744         debug!("walk_autoref(expr.hir_id={} cmt_base={:?} autoref={:?})",
 745                expr.hir_id,
 746                cmt_base,
 747                autoref);
 748
 749         match *autoref {
 750             adjustment::AutoBorrow::Ref(r, m) => {
 751                 self.delegate.borrow(expr.hir_id,
 752                                      expr.span,
 753                                      cmt_base,
 754                                      r,
 755                                      ty::BorrowKind::from_mutbl(m.into()),
 756                                      AutoRef);
 757             }
 758
 759             adjustment::AutoBorrow::RawPtr(m) => {
 760                 debug!("walk_autoref: expr.hir_id={} cmt_base={:?}",
 761                        expr.hir_id,
 762                        cmt_base);
 763
 764                 // Converting from a &T to *T (or &mut T to *mut T) is
 765                 // treated as borrowing it for the enclosing temporary
 766                 // scope.
 767                 let r = self.tcx().mk_region(ty::ReScope(
 768                     region::Scope {
 769                         id: expr.hir_id.local_id,
 770                         data: region::ScopeData::Node
 771                     }));
 772
 773                 self.delegate.borrow(expr.hir_id,
 774                                      expr.span,
 775                                      cmt_base,
 776                                      r,
 777                                      ty::BorrowKind::from_mutbl(m),
 778                                      AutoUnsafe);
 779             }
 780         }
 781     }
 782
 783     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 784         let mut mode = Unknown;
 785         for pat in &arm.pats {
 786             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 787         }
 788         mode
 789     }
 790
 791     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 792         for pat in &arm.pats {
 793             self.walk_pat(discr_cmt.clone(), &pat, mode);
 794         }
 795
 796         if let Some(hir::Guard::If(ref e)) = arm.guard {
 797             self.consume_expr(e)
 798         }
 799
 800         self.consume_expr(&arm.body);
 801     }
 802
 803     /// Walks a pat that occurs in isolation (i.e., top-level of fn argument or
 804     /// let binding, and *not* a match arm or nested pat.)
 805     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 806         let mut mode = Unknown;
 807         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 808         let mode = mode.match_mode();
 809         self.walk_pat(cmt_discr, pat, mode);
 810     }
 811
 812     /// Identifies any bindings within `pat` and accumulates within
 813     /// `mode` whether the overall pattern/match structure is a move,
 814     /// copy, or borrow.
 815     fn determine_pat_move_mode(&mut self,
 816                                cmt_discr: mc::cmt<'tcx>,
 817                                pat: &hir::Pat,
 818                                mode: &mut TrackMatchMode) {
 819         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr, pat);
 820
 821         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 822             if let PatKind::Binding(..) = pat.node {
 823                 let bm = *self.mc.tables.pat_binding_modes()
 824                                         .get(pat.hir_id)
 825                                         .expect("missing binding mode");
 826                 match bm {
 827                     ty::BindByReference(..) =>
 828                         mode.lub(BorrowingMatch),
 829                     ty::BindByValue(..) => {
 830                         match copy_or_move(&self.mc, self.param_env, &cmt_pat, PatBindingMove) {
 831                             Copy => mode.lub(CopyingMatch),
 832                             Move(..) => mode.lub(MovingMatch),
 833                         }
 834                     }
 835                 }
 836             }
 837         }));
 838     }
 839
 840     /// The core driver for walking a pattern; `match_mode` must be
 841     /// established up front, e.g., via `determine_pat_move_mode` (see
 842     /// also `walk_irrefutable_pat` for patterns that stand alone).
 843     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 844         debug!("walk_pat(cmt_discr={:?}, pat={:?})", cmt_discr, pat);
 845
 846         let tcx = self.tcx();
 847         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 848         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 849             if let PatKind::Binding(_, canonical_id, ..) = pat.node {
 850                 debug!(
 851                     "walk_pat: binding cmt_pat={:?} pat={:?} match_mode={:?}",
 852                     cmt_pat,
 853                     pat,
 854                     match_mode,
 855                 );
 856                 if let Some(&bm) = mc.tables.pat_binding_modes().get(pat.hir_id) {
 857                     debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
 858
 859                     // pat_ty: the type of the binding being produced.
 860                     let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
 861                     debug!("walk_pat: pat_ty={:?}", pat_ty);
 862
 863                     // Each match binding is effectively an assignment to the
 864                     // binding being produced.
 865                     let def = Res::Local(canonical_id);
 866                     if let Ok(ref binding_cmt) = mc.cat_res(pat.hir_id, pat.span, pat_ty, def) {
 867                         delegate.mutate(pat.hir_id, pat.span, binding_cmt, MutateMode::Init);
 868                     }
 869
 870                     // It is also a borrow or copy/move of the value being matched.
 871                     match bm {
 872                         ty::BindByReference(m) => {
 873                             if let ty::Ref(r, _, _) = pat_ty.sty {
 874                                 let bk = ty::BorrowKind::from_mutbl(m);
 875                                 delegate.borrow(pat.hir_id, pat.span, &cmt_pat, r, bk, RefBinding);
 876                             }
 877                         }
 878                         ty::BindByValue(..) => {
 879                             let mode = copy_or_move(mc, param_env, &cmt_pat, PatBindingMove);
 880                             debug!("walk_pat binding consuming pat");
 881                             delegate.consume_pat(pat, &cmt_pat, mode);
 882                         }
 883                     }
 884                 } else {
 885                     tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 886                 }
 887             }
 888         }));
 889
 890         // Do a second pass over the pattern, calling `matched_pat` on
 891         // the interior nodes (enum variants and structs), as opposed
 892         // to the above loop's visit of than the bindings that form
 893         // the leaves of the pattern tree structure.
 894         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 895             let qpath = match pat.node {
 896                 PatKind::Path(ref qpath) |
 897                 PatKind::TupleStruct(ref qpath, ..) |
 898                 PatKind::Struct(ref qpath, ..) => qpath,
 899                 _ => return
 900             };
 901             let res = mc.tables.qpath_res(qpath, pat.hir_id);
 902             match res {
 903                 Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_did) => {
 904                     let variant_did = mc.tcx.parent(variant_ctor_did).unwrap();
 905                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 906
 907                     debug!("variantctor downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 908                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 909                 }
 910                 Res::Def(DefKind::Variant, variant_did) => {
 911                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 912
 913                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 914                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 915                 }
 916                 Res::Def(DefKind::Struct, _)
 917                 | Res::Def(DefKind::Ctor(..), _)
 918                 | Res::Def(DefKind::Union, _)
 919                 | Res::Def(DefKind::TyAlias, _)
 920                 | Res::Def(DefKind::AssociatedTy, _)
 921                 | Res::SelfTy(..) => {
 922                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 923                     delegate.matched_pat(pat, &cmt_pat, match_mode);
 924                 }
 925                 _ => {}
 926             }
 927         }));
 928     }
 929
 930     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 931         debug!("walk_captures({:?})", closure_expr);
 932
 933         let closure_def_id = self.tcx().hir().local_def_id_from_hir_id(closure_expr.hir_id);
 934         if let Some(upvars) = self.tcx().upvars(closure_def_id) {
 935             for upvar in upvars.iter() {
 936                 let var_hir_id = upvar.var_id();
 937                 let upvar_id = ty::UpvarId {
 938                     var_path: ty::UpvarPath { hir_id: var_hir_id },
 939                     closure_expr_id: closure_def_id.to_local(),
 940                 };
 941                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 942                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.hir_id,
 943                                                                    fn_decl_span,
 944                                                                    upvar));
 945                 match upvar_capture {
 946                     ty::UpvarCapture::ByValue => {
 947                         let mode = copy_or_move(&self.mc,
 948                                                 self.param_env,
 949                                                 &cmt_var,
 950                                                 CaptureMove);
 951                         self.delegate.consume(closure_expr.hir_id, upvar.span, &cmt_var, mode);
 952                     }
 953                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 954                         self.delegate.borrow(closure_expr.hir_id,
 955                                              fn_decl_span,
 956                                              &cmt_var,
 957                                              upvar_borrow.region,
 958                                              upvar_borrow.kind,
 959                                              ClosureCapture(upvar.span));
 960                     }
 961                 }
 962             }
 963         }
 964     }
 965
 966     fn cat_captured_var(&mut self,
 967                         closure_hir_id: hir::HirId,
 968                         closure_span: Span,
 969                         upvar: &hir::Upvar)
 970                         -> mc::McResult<mc::cmt_<'tcx>> {
 971         // Create the cmt for the variable being borrowed, from the
 972         // caller's perspective
 973         let var_hir_id = upvar.var_id();
 974         let var_ty = self.mc.node_ty(var_hir_id)?;
 975         self.mc.cat_res(closure_hir_id, closure_span, var_ty, upvar.res)
 976     }
 977 }
 978
 979 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 980                                 param_env: ty::ParamEnv<'tcx>,
 981                                 cmt: &mc::cmt_<'tcx>,
 982                                 move_reason: MoveReason)
 983                                 -> ConsumeMode
 984 {
 985     if !mc.type_is_copy_modulo_regions(param_env, cmt.ty, cmt.span) {
 986         Move(move_reason)
 987     } else {
 988         Copy
 989     }
 990 }