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::Def;
  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, TyCtxt, adjustment};
  18
  19 use crate::hir::{self, PatKind};
  20 use rustc_data_structures::sync::Lrc;
  21 use std::rc::Rc;
  22 use syntax::ast;
  23 use syntax::ptr::P;
  24 use syntax_pos::Span;
  25 use crate::util::nodemap::ItemLocalSet;
  26
  27 ///////////////////////////////////////////////////////////////////////////
  28 // The Delegate trait
  29
  30 /// This trait defines the callbacks you can expect to receive when
  31 /// employing the ExprUseVisitor.
  32 pub trait Delegate<'tcx> {
  33     // The value found at `cmt` is either copied or moved, depending
  34     // on mode.
  35     fn consume(&mut self,
  36                consume_id: hir::HirId,
  37                consume_span: Span,
  38                cmt: &mc::cmt_<'tcx>,
  39                mode: ConsumeMode);
  40
  41     // The value found at `cmt` has been determined to match the
  42     // pattern binding `matched_pat`, and its subparts are being
  43     // copied or moved depending on `mode`.  Note that `matched_pat`
  44     // is called on all variant/structs in the pattern (i.e., the
  45     // interior nodes of the pattern's tree structure) while
  46     // consume_pat is called on the binding identifiers in the pattern
  47     // (which are leaves of the pattern's tree structure).
  48     //
  49     // Note that variants/structs and identifiers are disjoint; thus
  50     // `matched_pat` and `consume_pat` are never both called on the
  51     // same input pattern structure (though of `consume_pat` can be
  52     // called on a subpart of an input passed to `matched_pat).
  53     fn matched_pat(&mut self,
  54                    matched_pat: &hir::Pat,
  55                    cmt: &mc::cmt_<'tcx>,
  56                    mode: MatchMode);
  57
  58     // The value found at `cmt` is either copied or moved via the
  59     // pattern binding `consume_pat`, depending on mode.
  60     fn consume_pat(&mut self,
  61                    consume_pat: &hir::Pat,
  62                    cmt: &mc::cmt_<'tcx>,
  63                    mode: ConsumeMode);
  64
  65     // The value found at `borrow` is being borrowed at the point
  66     // `borrow_id` for the region `loan_region` with kind `bk`.
  67     fn borrow(&mut self,
  68               borrow_id: hir::HirId,
  69               borrow_span: Span,
  70               cmt: &mc::cmt_<'tcx>,
  71               loan_region: ty::Region<'tcx>,
  72               bk: ty::BorrowKind,
  73               loan_cause: LoanCause);
  74
  75     // The local variable `id` is declared but not initialized.
  76     fn decl_without_init(&mut self,
  77                          id: ast::NodeId,
  78                          span: Span);
  79
  80     // The path at `cmt` is being assigned to.
  81     fn mutate(&mut self,
  82               assignment_id: hir::HirId,
  83               assignment_span: Span,
  84               assignee_cmt: &mc::cmt_<'tcx>,
  85               mode: MutateMode);
  86 }
  87
  88 #[derive(Copy, Clone, PartialEq, Debug)]
  89 pub enum LoanCause {
  90     ClosureCapture(Span),
  91     AddrOf,
  92     AutoRef,
  93     AutoUnsafe,
  94     RefBinding,
  95     OverloadedOperator,
  96     ClosureInvocation,
  97     ForLoop,
  98     MatchDiscriminant
  99 }
 100
 101 #[derive(Copy, Clone, PartialEq, Debug)]
 102 pub enum ConsumeMode {
 103     Copy,                // reference to x where x has a type that copies
 104     Move(MoveReason),    // reference to x where x has a type that moves
 105 }
 106
 107 #[derive(Copy, Clone, PartialEq, Debug)]
 108 pub enum MoveReason {
 109     DirectRefMove,
 110     PatBindingMove,
 111     CaptureMove,
 112 }
 113
 114 #[derive(Copy, Clone, PartialEq, Debug)]
 115 pub enum MatchMode {
 116     NonBindingMatch,
 117     BorrowingMatch,
 118     CopyingMatch,
 119     MovingMatch,
 120 }
 121
 122 #[derive(Copy, Clone, PartialEq, Debug)]
 123 enum TrackMatchMode {
 124     Unknown,
 125     Definite(MatchMode),
 126     Conflicting,
 127 }
 128
 129 impl TrackMatchMode {
 130     // Builds up the whole match mode for a pattern from its constituent
 131     // parts.  The lattice looks like this:
 132     //
 133     //          Conflicting
 134     //            /     \
 135     //           /       \
 136     //      Borrowing   Moving
 137     //           \       /
 138     //            \     /
 139     //            Copying
 140     //               |
 141     //          NonBinding
 142     //               |
 143     //            Unknown
 144     //
 145     // examples:
 146     //
 147     // * `(_, some_int)` pattern is Copying, since
 148     //   NonBinding + Copying => Copying
 149     //
 150     // * `(some_int, some_box)` pattern is Moving, since
 151     //   Copying + Moving => Moving
 152     //
 153     // * `(ref x, some_box)` pattern is Conflicting, since
 154     //   Borrowing + Moving => Conflicting
 155     //
 156     // Note that the `Unknown` and `Conflicting` states are
 157     // represented separately from the other more interesting
 158     // `Definite` states, which simplifies logic here somewhat.
 159     fn lub(&mut self, mode: MatchMode) {
 160         *self = match (*self, mode) {
 161             // Note that clause order below is very significant.
 162             (Unknown, new) => Definite(new),
 163             (Definite(old), new) if old == new => Definite(old),
 164
 165             (Definite(old), NonBindingMatch) => Definite(old),
 166             (Definite(NonBindingMatch), new) => Definite(new),
 167
 168             (Definite(old), CopyingMatch) => Definite(old),
 169             (Definite(CopyingMatch), new) => Definite(new),
 170
 171             (Definite(_), _) => Conflicting,
 172             (Conflicting, _) => *self,
 173         };
 174     }
 175
 176     fn match_mode(&self) -> MatchMode {
 177         match *self {
 178             Unknown => NonBindingMatch,
 179             Definite(mode) => mode,
 180             Conflicting => {
 181                 // Conservatively return MovingMatch to let the
 182                 // compiler continue to make progress.
 183                 MovingMatch
 184             }
 185         }
 186     }
 187 }
 188
 189 #[derive(Copy, Clone, PartialEq, Debug)]
 190 pub enum MutateMode {
 191     Init,
 192     JustWrite,    // x = y
 193     WriteAndRead, // x += y
 194 }
 195
 196 #[derive(Copy, Clone)]
 197 enum OverloadedCallType {
 198     FnOverloadedCall,
 199     FnMutOverloadedCall,
 200     FnOnceOverloadedCall,
 201 }
 202
 203 impl OverloadedCallType {
 204     fn from_trait_id(tcx: TyCtxt<'_, '_, '_>, trait_id: DefId) -> OverloadedCallType {
 205         for &(maybe_function_trait, overloaded_call_type) in &[
 206             (tcx.lang_items().fn_once_trait(), FnOnceOverloadedCall),
 207             (tcx.lang_items().fn_mut_trait(), FnMutOverloadedCall),
 208             (tcx.lang_items().fn_trait(), FnOverloadedCall)
 209         ] {
 210             match maybe_function_trait {
 211                 Some(function_trait) if function_trait == trait_id => {
 212                     return overloaded_call_type
 213                 }
 214                 _ => continue,
 215             }
 216         }
 217
 218         bug!("overloaded call didn't map to known function trait")
 219     }
 220
 221     fn from_method_id(tcx: TyCtxt<'_, '_, '_>, method_id: DefId) -> OverloadedCallType {
 222         let method = tcx.associated_item(method_id);
 223         OverloadedCallType::from_trait_id(tcx, method.container.id())
 224     }
 225 }
 226
 227 ///////////////////////////////////////////////////////////////////////////
 228 // The ExprUseVisitor type
 229 //
 230 // This is the code that actually walks the tree.
 231 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 232     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 233     delegate: &'a mut dyn Delegate<'tcx>,
 234     param_env: ty::ParamEnv<'tcx>,
 235 }
 236
 237 // If the MC results in an error, it's because the type check
 238 // failed (or will fail, when the error is uncovered and reported
 239 // during writeback). In this case, we just ignore this part of the
 240 // code.
 241 //
 242 // Note that this macro appears similar to try!(), but, unlike try!(),
 243 // it does not propagate the error.
 244 macro_rules! return_if_err {
 245     ($inp: expr) => (
 246         match $inp {
 247             Ok(v) => v,
 248             Err(()) => {
 249                 debug!("mc reported err");
 250                 return
 251             }
 252         }
 253     )
 254 }
 255
 256 impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
 257     /// Creates the ExprUseVisitor, configuring it with the various options provided:
 258     ///
 259     /// - `delegate` -- who receives the callbacks
 260     /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
 261     /// - `region_scope_tree` --- region scope tree for the code being analyzed
 262     /// - `tables` --- typeck results for the code being analyzed
 263     /// - `rvalue_promotable_map` --- if you care about rvalue promotion, then provide
 264     ///   the map here (it can be computed with `tcx.rvalue_promotable_map(def_id)`).
 265     ///   `None` means that rvalues will be given more conservative lifetimes.
 266     ///
 267     /// See also `with_infer`, which is used *during* typeck.
 268     pub fn new(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 269                tcx: TyCtxt<'a, 'tcx, 'tcx>,
 270                param_env: ty::ParamEnv<'tcx>,
 271                region_scope_tree: &'a region::ScopeTree,
 272                tables: &'a ty::TypeckTables<'tcx>,
 273                rvalue_promotable_map: Option<Lrc<ItemLocalSet>>)
 274                -> Self
 275     {
 276         ExprUseVisitor {
 277             mc: mc::MemCategorizationContext::new(tcx,
 278                                                   region_scope_tree,
 279                                                   tables,
 280                                                   rvalue_promotable_map),
 281             delegate,
 282             param_env,
 283         }
 284     }
 285 }
 286
 287 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 288     pub fn with_infer(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 289                       infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 290                       param_env: ty::ParamEnv<'tcx>,
 291                       region_scope_tree: &'a region::ScopeTree,
 292                       tables: &'a ty::TypeckTables<'tcx>)
 293                       -> Self
 294     {
 295         ExprUseVisitor {
 296             mc: mc::MemCategorizationContext::with_infer(infcx, region_scope_tree, tables),
 297             delegate,
 298             param_env,
 299         }
 300     }
 301
 302     pub fn consume_body(&mut self, body: &hir::Body) {
 303         debug!("consume_body(body={:?})", body);
 304
 305         for arg in &body.arguments {
 306             let arg_ty = return_if_err!(self.mc.pat_ty_adjusted(&arg.pat));
 307             debug!("consume_body: arg_ty = {:?}", arg_ty);
 308
 309             let fn_body_scope_r =
 310                 self.tcx().mk_region(ty::ReScope(
 311                     region::Scope {
 312                         id: body.value.hir_id.local_id,
 313                         data: region::ScopeData::Node
 314                 }));
 315             let arg_cmt = Rc::new(self.mc.cat_rvalue(
 316                 arg.hir_id,
 317                 arg.pat.span,
 318                 fn_body_scope_r, // Args live only as long as the fn body.
 319                 arg_ty));
 320
 321             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 322         }
 323
 324         self.consume_expr(&body.value);
 325     }
 326
 327     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 328         self.mc.tcx
 329     }
 330
 331     fn delegate_consume(&mut self,
 332                         consume_id: hir::HirId,
 333                         consume_span: Span,
 334                         cmt: &mc::cmt_<'tcx>) {
 335         debug!("delegate_consume(consume_id={}, cmt={:?})",
 336                consume_id, cmt);
 337
 338         let mode = copy_or_move(&self.mc, self.param_env, cmt, DirectRefMove);
 339         self.delegate.consume(consume_id, consume_span, cmt, mode);
 340     }
 341
 342     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 343         for expr in exprs {
 344             self.consume_expr(&expr);
 345         }
 346     }
 347
 348     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 349         debug!("consume_expr(expr={:?})", expr);
 350
 351         let cmt = return_if_err!(self.mc.cat_expr(expr));
 352         self.delegate_consume(expr.hir_id, expr.span, &cmt);
 353         self.walk_expr(expr);
 354     }
 355
 356     fn mutate_expr(&mut self,
 357                    span: Span,
 358                    assignment_expr: &hir::Expr,
 359                    expr: &hir::Expr,
 360                    mode: MutateMode) {
 361         let cmt = return_if_err!(self.mc.cat_expr(expr));
 362         self.delegate.mutate(assignment_expr.hir_id, span, &cmt, mode);
 363         self.walk_expr(expr);
 364     }
 365
 366     fn borrow_expr(&mut self,
 367                    expr: &hir::Expr,
 368                    r: ty::Region<'tcx>,
 369                    bk: ty::BorrowKind,
 370                    cause: LoanCause) {
 371         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 372                expr, r, bk);
 373
 374         let cmt = return_if_err!(self.mc.cat_expr(expr));
 375         self.delegate.borrow(expr.hir_id, expr.span, &cmt, r, bk, cause);
 376
 377         self.walk_expr(expr)
 378     }
 379
 380     fn select_from_expr(&mut self, expr: &hir::Expr) {
 381         self.walk_expr(expr)
 382     }
 383
 384     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 385         debug!("walk_expr(expr={:?})", expr);
 386
 387         self.walk_adjustment(expr);
 388
 389         match expr.node {
 390             hir::ExprKind::Path(_) => { }
 391
 392             hir::ExprKind::Type(ref subexpr, _) => {
 393                 self.walk_expr(&subexpr)
 394             }
 395
 396             hir::ExprKind::Unary(hir::UnDeref, ref base) => { // *base
 397                 self.select_from_expr(&base);
 398             }
 399
 400             hir::ExprKind::Field(ref base, _) => { // base.f
 401                 self.select_from_expr(&base);
 402             }
 403
 404             hir::ExprKind::Index(ref lhs, ref rhs) => { // lhs[rhs]
 405                 self.select_from_expr(&lhs);
 406                 self.consume_expr(&rhs);
 407             }
 408
 409             hir::ExprKind::Call(ref callee, ref args) => { // callee(args)
 410                 self.walk_callee(expr, &callee);
 411                 self.consume_exprs(args);
 412             }
 413
 414             hir::ExprKind::MethodCall(.., ref args) => { // callee.m(args)
 415                 self.consume_exprs(args);
 416             }
 417
 418             hir::ExprKind::Struct(_, ref fields, ref opt_with) => {
 419                 self.walk_struct_expr(fields, opt_with);
 420             }
 421
 422             hir::ExprKind::Tup(ref exprs) => {
 423                 self.consume_exprs(exprs);
 424             }
 425
 426             hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 427                 self.consume_expr(&cond_expr);
 428                 self.walk_expr(&then_expr);
 429                 if let Some(ref else_expr) = *opt_else_expr {
 430                     self.consume_expr(&else_expr);
 431                 }
 432             }
 433
 434             hir::ExprKind::Match(ref discr, ref arms, _) => {
 435                 let discr_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&discr)));
 436                 let r = self.tcx().types.re_empty;
 437                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 438
 439                 // treatment of the discriminant is handled while walking the arms.
 440                 for arm in arms {
 441                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 442                     let mode = mode.match_mode();
 443                     self.walk_arm(discr_cmt.clone(), arm, mode);
 444                 }
 445             }
 446
 447             hir::ExprKind::Array(ref exprs) => {
 448                 self.consume_exprs(exprs);
 449             }
 450
 451             hir::ExprKind::AddrOf(m, ref base) => {   // &base
 452                 // make sure that the thing we are pointing out stays valid
 453                 // for the lifetime `scope_r` of the resulting ptr:
 454                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 455                 if let ty::Ref(r, _, _) = expr_ty.sty {
 456                     let bk = ty::BorrowKind::from_mutbl(m);
 457                     self.borrow_expr(&base, r, bk, AddrOf);
 458                 }
 459             }
 460
 461             hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
 462                 for (o, output) in ia.outputs.iter().zip(outputs) {
 463                     if o.is_indirect {
 464                         self.consume_expr(output);
 465                     } else {
 466                         self.mutate_expr(
 467                             output.span,
 468                             expr,
 469                             output,
 470                             if o.is_rw {
 471                                 MutateMode::WriteAndRead
 472                             } else {
 473                                 MutateMode::JustWrite
 474                             },
 475                         );
 476                     }
 477                 }
 478                 self.consume_exprs(inputs);
 479             }
 480
 481             hir::ExprKind::Continue(..) |
 482             hir::ExprKind::Lit(..) |
 483             hir::ExprKind::Err => {}
 484
 485             hir::ExprKind::Loop(ref blk, _, _) => {
 486                 self.walk_block(&blk);
 487             }
 488
 489             hir::ExprKind::While(ref cond_expr, ref blk, _) => {
 490                 self.consume_expr(&cond_expr);
 491                 self.walk_block(&blk);
 492             }
 493
 494             hir::ExprKind::Unary(_, ref lhs) => {
 495                 self.consume_expr(&lhs);
 496             }
 497
 498             hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
 499                 self.consume_expr(&lhs);
 500                 self.consume_expr(&rhs);
 501             }
 502
 503             hir::ExprKind::Block(ref blk, _) => {
 504                 self.walk_block(&blk);
 505             }
 506
 507             hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
 508                 if let Some(ref expr) = *opt_expr {
 509                     self.consume_expr(&expr);
 510                 }
 511             }
 512
 513             hir::ExprKind::Assign(ref lhs, ref rhs) => {
 514                 self.mutate_expr(expr.span, expr, &lhs, MutateMode::JustWrite);
 515                 self.consume_expr(&rhs);
 516             }
 517
 518             hir::ExprKind::Cast(ref base, _) => {
 519                 self.consume_expr(&base);
 520             }
 521
 522             hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
 523                 if self.mc.tables.is_method_call(expr) {
 524                     self.consume_expr(lhs);
 525                 } else {
 526                     self.mutate_expr(expr.span, expr, &lhs, MutateMode::WriteAndRead);
 527                 }
 528                 self.consume_expr(&rhs);
 529             }
 530
 531             hir::ExprKind::Repeat(ref base, _) => {
 532                 self.consume_expr(&base);
 533             }
 534
 535             hir::ExprKind::Closure(.., fn_decl_span, _) => {
 536                 self.walk_captures(expr, fn_decl_span)
 537             }
 538
 539             hir::ExprKind::Box(ref base) => {
 540                 self.consume_expr(&base);
 541             }
 542
 543             hir::ExprKind::Yield(ref value) => {
 544                 self.consume_expr(&value);
 545             }
 546         }
 547     }
 548
 549     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 550         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 551         debug!("walk_callee: callee={:?} callee_ty={:?}",
 552                callee, callee_ty);
 553         match callee_ty.sty {
 554             ty::FnDef(..) | ty::FnPtr(_) => {
 555                 self.consume_expr(callee);
 556             }
 557             ty::Error => { }
 558             _ => {
 559                 if let Some(def) = self.mc.tables.type_dependent_defs().get(call.hir_id) {
 560                     let def_id = def.def_id();
 561                     let call_scope = region::Scope {
 562                         id: call.hir_id.local_id,
 563                         data: region::ScopeData::Node
 564                     };
 565                     match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 566                         FnMutOverloadedCall => {
 567                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 568                             self.borrow_expr(callee,
 569                                             call_scope_r,
 570                                             ty::MutBorrow,
 571                                             ClosureInvocation);
 572                         }
 573                         FnOverloadedCall => {
 574                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 575                             self.borrow_expr(callee,
 576                                             call_scope_r,
 577                                             ty::ImmBorrow,
 578                                             ClosureInvocation);
 579                         }
 580                         FnOnceOverloadedCall => self.consume_expr(callee),
 581                     }
 582                 } else {
 583                     self.tcx().sess.delay_span_bug(call.span,
 584                                                    "no type-dependent def for overloaded call");
 585                 }
 586             }
 587         }
 588     }
 589
 590     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 591         match stmt.node {
 592             hir::StmtKind::Local(ref local) => {
 593                 self.walk_local(&local);
 594             }
 595
 596             hir::StmtKind::Item(_) => {
 597                 // we don't visit nested items in this visitor,
 598                 // only the fn body we were given.
 599             }
 600
 601             hir::StmtKind::Expr(ref expr) |
 602             hir::StmtKind::Semi(ref expr) => {
 603                 self.consume_expr(&expr);
 604             }
 605         }
 606     }
 607
 608     fn walk_local(&mut self, local: &hir::Local) {
 609         match local.init {
 610             None => {
 611                 local.pat.each_binding(|_, hir_id, span, _| {
 612                     let node_id = self.mc.tcx.hir().hir_to_node_id(hir_id);
 613                     self.delegate.decl_without_init(node_id, span);
 614                 })
 615             }
 616
 617             Some(ref expr) => {
 618                 // Variable declarations with
 619                 // initializers are considered
 620                 // "assigns", which is handled by
 621                 // `walk_pat`:
 622                 self.walk_expr(&expr);
 623                 let init_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&expr)));
 624                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 625             }
 626         }
 627     }
 628
 629     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 630     /// depending on its type.
 631     fn walk_block(&mut self, blk: &hir::Block) {
 632         debug!("walk_block(blk.hir_id={})", blk.hir_id);
 633
 634         for stmt in &blk.stmts {
 635             self.walk_stmt(stmt);
 636         }
 637
 638         if let Some(ref tail_expr) = blk.expr {
 639             self.consume_expr(&tail_expr);
 640         }
 641     }
 642
 643     fn walk_struct_expr(&mut self,
 644                         fields: &[hir::Field],
 645                         opt_with: &Option<P<hir::Expr>>) {
 646         // Consume the expressions supplying values for each field.
 647         for field in fields {
 648             self.consume_expr(&field.expr);
 649         }
 650
 651         let with_expr = match *opt_with {
 652             Some(ref w) => &**w,
 653             None => { return; }
 654         };
 655
 656         let with_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&with_expr)));
 657
 658         // Select just those fields of the `with`
 659         // expression that will actually be used
 660         match with_cmt.ty.sty {
 661             ty::Adt(adt, substs) if adt.is_struct() => {
 662                 // Consume those fields of the with expression that are needed.
 663                 for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() {
 664                     let is_mentioned = fields.iter().any(|f| {
 665                         self.tcx().field_index(f.hir_id, self.mc.tables) == f_index
 666                     });
 667                     if !is_mentioned {
 668                         let cmt_field = self.mc.cat_field(
 669                             &*with_expr,
 670                             with_cmt.clone(),
 671                             f_index,
 672                             with_field.ident,
 673                             with_field.ty(self.tcx(), substs)
 674                         );
 675                         self.delegate_consume(with_expr.hir_id, with_expr.span, &cmt_field);
 676                     }
 677                 }
 678             }
 679             _ => {
 680                 // the base expression should always evaluate to a
 681                 // struct; however, when EUV is run during typeck, it
 682                 // may not. This will generate an error earlier in typeck,
 683                 // so we can just ignore it.
 684                 if !self.tcx().sess.has_errors() {
 685                     span_bug!(
 686                         with_expr.span,
 687                         "with expression doesn't evaluate to a struct");
 688                 }
 689             }
 690         }
 691
 692         // walk the with expression so that complex expressions
 693         // are properly handled.
 694         self.walk_expr(with_expr);
 695     }
 696
 697     // Invoke the appropriate delegate calls for anything that gets
 698     // consumed or borrowed as part of the automatic adjustment
 699     // process.
 700     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 701         let adjustments = self.mc.tables.expr_adjustments(expr);
 702         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 703         for adjustment in adjustments {
 704             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 705             match adjustment.kind {
 706                 adjustment::Adjust::NeverToAny |
 707                 adjustment::Adjust::ReifyFnPointer |
 708                 adjustment::Adjust::UnsafeFnPointer |
 709                 adjustment::Adjust::ClosureFnPointer |
 710                 adjustment::Adjust::MutToConstPointer |
 711                 adjustment::Adjust::Unsize => {
 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 = Def::Local(canonical_id);
 866                     if let Ok(ref binding_cmt) = mc.cat_def(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 def = mc.tables.qpath_def(qpath, pat.hir_id);
 902             match def {
 903                 Def::Variant(variant_did) |
 904                 Def::VariantCtor(variant_did, ..) => {
 905                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 906
 907                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 908                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 909                 }
 910                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 911                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 912                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 913                     delegate.matched_pat(pat, &cmt_pat, match_mode);
 914                 }
 915                 _ => {}
 916             }
 917         }));
 918     }
 919
 920     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 921         debug!("walk_captures({:?})", closure_expr);
 922
 923         let closure_node_id = self.tcx().hir().hir_to_node_id(closure_expr.hir_id);
 924         let closure_def_id = self.tcx().hir().local_def_id(closure_node_id);
 925         self.tcx().with_freevars(closure_node_id, |freevars| {
 926             for freevar in freevars {
 927                 let var_hir_id = self.tcx().hir().node_to_hir_id(freevar.var_id());
 928                 let upvar_id = ty::UpvarId {
 929                     var_path: ty::UpvarPath { hir_id: var_hir_id },
 930                     closure_expr_id: closure_def_id.to_local(),
 931                 };
 932                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 933                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.hir_id,
 934                                                                    fn_decl_span,
 935                                                                    freevar));
 936                 match upvar_capture {
 937                     ty::UpvarCapture::ByValue => {
 938                         let mode = copy_or_move(&self.mc,
 939                                                 self.param_env,
 940                                                 &cmt_var,
 941                                                 CaptureMove);
 942                         self.delegate.consume(closure_expr.hir_id, freevar.span, &cmt_var, mode);
 943                     }
 944                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 945                         self.delegate.borrow(closure_expr.hir_id,
 946                                              fn_decl_span,
 947                                              &cmt_var,
 948                                              upvar_borrow.region,
 949                                              upvar_borrow.kind,
 950                                              ClosureCapture(freevar.span));
 951                     }
 952                 }
 953             }
 954         });
 955     }
 956
 957     fn cat_captured_var(&mut self,
 958                         closure_hir_id: hir::HirId,
 959                         closure_span: Span,
 960                         upvar: &hir::Freevar)
 961                         -> mc::McResult<mc::cmt_<'tcx>> {
 962         // Create the cmt for the variable being borrowed, from the
 963         // caller's perspective
 964         let var_hir_id = self.tcx().hir().node_to_hir_id(upvar.var_id());
 965         let var_ty = self.mc.node_ty(var_hir_id)?;
 966         self.mc.cat_def(closure_hir_id, closure_span, var_ty, upvar.def)
 967     }
 968 }
 969
 970 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 971                                 param_env: ty::ParamEnv<'tcx>,
 972                                 cmt: &mc::cmt_<'tcx>,
 973                                 move_reason: MoveReason)
 974                                 -> ConsumeMode
 975 {
 976     if !mc.type_is_copy_modulo_regions(param_env, cmt.ty, cmt.span) {
 977         Move(move_reason)
 978     } else {
 979         Copy
 980     }
 981 }