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::Match(ref discr, ref arms, _) => {
 428                 let discr_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&discr)));
 429                 let r = self.tcx().lifetimes.re_empty;
 430                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 431
 432                 // treatment of the discriminant is handled while walking the arms.
 433                 for arm in arms {
 434                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 435                     let mode = mode.match_mode();
 436                     self.walk_arm(discr_cmt.clone(), arm, mode);
 437                 }
 438             }
 439
 440             hir::ExprKind::Array(ref exprs) => {
 441                 self.consume_exprs(exprs);
 442             }
 443
 444             hir::ExprKind::AddrOf(m, ref base) => {   // &base
 445                 // make sure that the thing we are pointing out stays valid
 446                 // for the lifetime `scope_r` of the resulting ptr:
 447                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 448                 if let ty::Ref(r, _, _) = expr_ty.sty {
 449                     let bk = ty::BorrowKind::from_mutbl(m);
 450                     self.borrow_expr(&base, r, bk, AddrOf);
 451                 }
 452             }
 453
 454             hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
 455                 for (o, output) in ia.outputs.iter().zip(outputs) {
 456                     if o.is_indirect {
 457                         self.consume_expr(output);
 458                     } else {
 459                         self.mutate_expr(
 460                             output.span,
 461                             expr,
 462                             output,
 463                             if o.is_rw {
 464                                 MutateMode::WriteAndRead
 465                             } else {
 466                                 MutateMode::JustWrite
 467                             },
 468                         );
 469                     }
 470                 }
 471                 self.consume_exprs(inputs);
 472             }
 473
 474             hir::ExprKind::Continue(..) |
 475             hir::ExprKind::Lit(..) |
 476             hir::ExprKind::Err => {}
 477
 478             hir::ExprKind::Loop(ref blk, _, _) => {
 479                 self.walk_block(&blk);
 480             }
 481
 482             hir::ExprKind::While(ref cond_expr, ref blk, _) => {
 483                 self.consume_expr(&cond_expr);
 484                 self.walk_block(&blk);
 485             }
 486
 487             hir::ExprKind::Unary(_, ref lhs) => {
 488                 self.consume_expr(&lhs);
 489             }
 490
 491             hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
 492                 self.consume_expr(&lhs);
 493                 self.consume_expr(&rhs);
 494             }
 495
 496             hir::ExprKind::Block(ref blk, _) => {
 497                 self.walk_block(&blk);
 498             }
 499
 500             hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
 501                 if let Some(ref expr) = *opt_expr {
 502                     self.consume_expr(&expr);
 503                 }
 504             }
 505
 506             hir::ExprKind::Assign(ref lhs, ref rhs) => {
 507                 self.mutate_expr(expr.span, expr, &lhs, MutateMode::JustWrite);
 508                 self.consume_expr(&rhs);
 509             }
 510
 511             hir::ExprKind::Cast(ref base, _) => {
 512                 self.consume_expr(&base);
 513             }
 514
 515             hir::ExprKind::DropTemps(ref expr) => {
 516                 self.consume_expr(&expr);
 517             }
 518
 519             hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
 520                 if self.mc.tables.is_method_call(expr) {
 521                     self.consume_expr(lhs);
 522                 } else {
 523                     self.mutate_expr(expr.span, expr, &lhs, MutateMode::WriteAndRead);
 524                 }
 525                 self.consume_expr(&rhs);
 526             }
 527
 528             hir::ExprKind::Repeat(ref base, _) => {
 529                 self.consume_expr(&base);
 530             }
 531
 532             hir::ExprKind::Closure(_, _, body_id, fn_decl_span, _) => {
 533                 self.delegate.nested_body(body_id);
 534                 self.walk_captures(expr, fn_decl_span);
 535             }
 536
 537             hir::ExprKind::Box(ref base) => {
 538                 self.consume_expr(&base);
 539             }
 540
 541             hir::ExprKind::Yield(ref value) => {
 542                 self.consume_expr(&value);
 543             }
 544         }
 545     }
 546
 547     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 548         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 549         debug!("walk_callee: callee={:?} callee_ty={:?}",
 550                callee, callee_ty);
 551         match callee_ty.sty {
 552             ty::FnDef(..) | ty::FnPtr(_) => {
 553                 self.consume_expr(callee);
 554             }
 555             ty::Error => { }
 556             _ => {
 557                 if let Some(def_id) = self.mc.tables.type_dependent_def_id(call.hir_id) {
 558                     let call_scope = region::Scope {
 559                         id: call.hir_id.local_id,
 560                         data: region::ScopeData::Node
 561                     };
 562                     match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 563                         FnMutOverloadedCall => {
 564                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 565                             self.borrow_expr(callee,
 566                                             call_scope_r,
 567                                             ty::MutBorrow,
 568                                             ClosureInvocation);
 569                         }
 570                         FnOverloadedCall => {
 571                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 572                             self.borrow_expr(callee,
 573                                             call_scope_r,
 574                                             ty::ImmBorrow,
 575                                             ClosureInvocation);
 576                         }
 577                         FnOnceOverloadedCall => self.consume_expr(callee),
 578                     }
 579                 } else {
 580                     self.tcx().sess.delay_span_bug(call.span,
 581                                                    "no type-dependent def for overloaded call");
 582                 }
 583             }
 584         }
 585     }
 586
 587     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 588         match stmt.node {
 589             hir::StmtKind::Local(ref local) => {
 590                 self.walk_local(&local);
 591             }
 592
 593             hir::StmtKind::Item(_) => {
 594                 // we don't visit nested items in this visitor,
 595                 // only the fn body we were given.
 596             }
 597
 598             hir::StmtKind::Expr(ref expr) |
 599             hir::StmtKind::Semi(ref expr) => {
 600                 self.consume_expr(&expr);
 601             }
 602         }
 603     }
 604
 605     fn walk_local(&mut self, local: &hir::Local) {
 606         match local.init {
 607             None => {
 608                 local.pat.each_binding(|_, hir_id, span, _| {
 609                     self.delegate.decl_without_init(hir_id, span);
 610                 })
 611             }
 612
 613             Some(ref expr) => {
 614                 // Variable declarations with
 615                 // initializers are considered
 616                 // "assigns", which is handled by
 617                 // `walk_pat`:
 618                 self.walk_expr(&expr);
 619                 let init_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&expr)));
 620                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 621             }
 622         }
 623     }
 624
 625     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 626     /// depending on its type.
 627     fn walk_block(&mut self, blk: &hir::Block) {
 628         debug!("walk_block(blk.hir_id={})", blk.hir_id);
 629
 630         for stmt in &blk.stmts {
 631             self.walk_stmt(stmt);
 632         }
 633
 634         if let Some(ref tail_expr) = blk.expr {
 635             self.consume_expr(&tail_expr);
 636         }
 637     }
 638
 639     fn walk_struct_expr(&mut self,
 640                         fields: &[hir::Field],
 641                         opt_with: &Option<P<hir::Expr>>) {
 642         // Consume the expressions supplying values for each field.
 643         for field in fields {
 644             self.consume_expr(&field.expr);
 645         }
 646
 647         let with_expr = match *opt_with {
 648             Some(ref w) => &**w,
 649             None => { return; }
 650         };
 651
 652         let with_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&with_expr)));
 653
 654         // Select just those fields of the `with`
 655         // expression that will actually be used
 656         match with_cmt.ty.sty {
 657             ty::Adt(adt, substs) if adt.is_struct() => {
 658                 // Consume those fields of the with expression that are needed.
 659                 for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() {
 660                     let is_mentioned = fields.iter().any(|f| {
 661                         self.tcx().field_index(f.hir_id, self.mc.tables) == f_index
 662                     });
 663                     if !is_mentioned {
 664                         let cmt_field = self.mc.cat_field(
 665                             &*with_expr,
 666                             with_cmt.clone(),
 667                             f_index,
 668                             with_field.ident,
 669                             with_field.ty(self.tcx(), substs)
 670                         );
 671                         self.delegate_consume(with_expr.hir_id, with_expr.span, &cmt_field);
 672                     }
 673                 }
 674             }
 675             _ => {
 676                 // the base expression should always evaluate to a
 677                 // struct; however, when EUV is run during typeck, it
 678                 // may not. This will generate an error earlier in typeck,
 679                 // so we can just ignore it.
 680                 if !self.tcx().sess.has_errors() {
 681                     span_bug!(
 682                         with_expr.span,
 683                         "with expression doesn't evaluate to a struct");
 684                 }
 685             }
 686         }
 687
 688         // walk the with expression so that complex expressions
 689         // are properly handled.
 690         self.walk_expr(with_expr);
 691     }
 692
 693     // Invoke the appropriate delegate calls for anything that gets
 694     // consumed or borrowed as part of the automatic adjustment
 695     // process.
 696     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 697         let adjustments = self.mc.tables.expr_adjustments(expr);
 698         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 699         for adjustment in adjustments {
 700             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 701             match adjustment.kind {
 702                 adjustment::Adjust::NeverToAny |
 703                 adjustment::Adjust::Pointer(_)  => {
 704                     // Creating a closure/fn-pointer or unsizing consumes
 705                     // the input and stores it into the resulting rvalue.
 706                     self.delegate_consume(expr.hir_id, expr.span, &cmt);
 707                 }
 708
 709                 adjustment::Adjust::Deref(None) => {}
 710
 711                 // Autoderefs for overloaded Deref calls in fact reference
 712                 // their receiver. That is, if we have `(*x)` where `x`
 713                 // is of type `Rc<T>`, then this in fact is equivalent to
 714                 // `x.deref()`. Since `deref()` is declared with `&self`,
 715                 // this is an autoref of `x`.
 716                 adjustment::Adjust::Deref(Some(ref deref)) => {
 717                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 718                     self.delegate.borrow(expr.hir_id, expr.span, &cmt, deref.region, bk, AutoRef);
 719                 }
 720
 721                 adjustment::Adjust::Borrow(ref autoref) => {
 722                     self.walk_autoref(expr, &cmt, autoref);
 723                 }
 724             }
 725             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 726         }
 727     }
 728
 729     /// Walks the autoref `autoref` applied to the autoderef'd
 730     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 731     /// after all relevant autoderefs have occurred.
 732     fn walk_autoref(&mut self,
 733                     expr: &hir::Expr,
 734                     cmt_base: &mc::cmt_<'tcx>,
 735                     autoref: &adjustment::AutoBorrow<'tcx>) {
 736         debug!("walk_autoref(expr.hir_id={} cmt_base={:?} autoref={:?})",
 737                expr.hir_id,
 738                cmt_base,
 739                autoref);
 740
 741         match *autoref {
 742             adjustment::AutoBorrow::Ref(r, m) => {
 743                 self.delegate.borrow(expr.hir_id,
 744                                      expr.span,
 745                                      cmt_base,
 746                                      r,
 747                                      ty::BorrowKind::from_mutbl(m.into()),
 748                                      AutoRef);
 749             }
 750
 751             adjustment::AutoBorrow::RawPtr(m) => {
 752                 debug!("walk_autoref: expr.hir_id={} cmt_base={:?}",
 753                        expr.hir_id,
 754                        cmt_base);
 755
 756                 // Converting from a &T to *T (or &mut T to *mut T) is
 757                 // treated as borrowing it for the enclosing temporary
 758                 // scope.
 759                 let r = self.tcx().mk_region(ty::ReScope(
 760                     region::Scope {
 761                         id: expr.hir_id.local_id,
 762                         data: region::ScopeData::Node
 763                     }));
 764
 765                 self.delegate.borrow(expr.hir_id,
 766                                      expr.span,
 767                                      cmt_base,
 768                                      r,
 769                                      ty::BorrowKind::from_mutbl(m),
 770                                      AutoUnsafe);
 771             }
 772         }
 773     }
 774
 775     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 776         let mut mode = Unknown;
 777         for pat in &arm.pats {
 778             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 779         }
 780         mode
 781     }
 782
 783     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 784         for pat in &arm.pats {
 785             self.walk_pat(discr_cmt.clone(), &pat, mode);
 786         }
 787
 788         if let Some(hir::Guard::If(ref e)) = arm.guard {
 789             self.consume_expr(e)
 790         }
 791
 792         self.consume_expr(&arm.body);
 793     }
 794
 795     /// Walks a pat that occurs in isolation (i.e., top-level of fn argument or
 796     /// let binding, and *not* a match arm or nested pat.)
 797     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 798         let mut mode = Unknown;
 799         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 800         let mode = mode.match_mode();
 801         self.walk_pat(cmt_discr, pat, mode);
 802     }
 803
 804     /// Identifies any bindings within `pat` and accumulates within
 805     /// `mode` whether the overall pattern/match structure is a move,
 806     /// copy, or borrow.
 807     fn determine_pat_move_mode(&mut self,
 808                                cmt_discr: mc::cmt<'tcx>,
 809                                pat: &hir::Pat,
 810                                mode: &mut TrackMatchMode) {
 811         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr, pat);
 812
 813         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 814             if let PatKind::Binding(..) = pat.node {
 815                 let bm = *self.mc.tables.pat_binding_modes()
 816                                         .get(pat.hir_id)
 817                                         .expect("missing binding mode");
 818                 match bm {
 819                     ty::BindByReference(..) =>
 820                         mode.lub(BorrowingMatch),
 821                     ty::BindByValue(..) => {
 822                         match copy_or_move(&self.mc, self.param_env, &cmt_pat, PatBindingMove) {
 823                             Copy => mode.lub(CopyingMatch),
 824                             Move(..) => mode.lub(MovingMatch),
 825                         }
 826                     }
 827                 }
 828             }
 829         }));
 830     }
 831
 832     /// The core driver for walking a pattern; `match_mode` must be
 833     /// established up front, e.g., via `determine_pat_move_mode` (see
 834     /// also `walk_irrefutable_pat` for patterns that stand alone).
 835     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 836         debug!("walk_pat(cmt_discr={:?}, pat={:?})", cmt_discr, pat);
 837
 838         let tcx = self.tcx();
 839         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 840         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 841             if let PatKind::Binding(_, canonical_id, ..) = pat.node {
 842                 debug!(
 843                     "walk_pat: binding cmt_pat={:?} pat={:?} match_mode={:?}",
 844                     cmt_pat,
 845                     pat,
 846                     match_mode,
 847                 );
 848                 if let Some(&bm) = mc.tables.pat_binding_modes().get(pat.hir_id) {
 849                     debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
 850
 851                     // pat_ty: the type of the binding being produced.
 852                     let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
 853                     debug!("walk_pat: pat_ty={:?}", pat_ty);
 854
 855                     // Each match binding is effectively an assignment to the
 856                     // binding being produced.
 857                     let def = Res::Local(canonical_id);
 858                     if let Ok(ref binding_cmt) = mc.cat_res(pat.hir_id, pat.span, pat_ty, def) {
 859                         delegate.mutate(pat.hir_id, pat.span, binding_cmt, MutateMode::Init);
 860                     }
 861
 862                     // It is also a borrow or copy/move of the value being matched.
 863                     match bm {
 864                         ty::BindByReference(m) => {
 865                             if let ty::Ref(r, _, _) = pat_ty.sty {
 866                                 let bk = ty::BorrowKind::from_mutbl(m);
 867                                 delegate.borrow(pat.hir_id, pat.span, &cmt_pat, r, bk, RefBinding);
 868                             }
 869                         }
 870                         ty::BindByValue(..) => {
 871                             let mode = copy_or_move(mc, param_env, &cmt_pat, PatBindingMove);
 872                             debug!("walk_pat binding consuming pat");
 873                             delegate.consume_pat(pat, &cmt_pat, mode);
 874                         }
 875                     }
 876                 } else {
 877                     tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 878                 }
 879             }
 880         }));
 881
 882         // Do a second pass over the pattern, calling `matched_pat` on
 883         // the interior nodes (enum variants and structs), as opposed
 884         // to the above loop's visit of than the bindings that form
 885         // the leaves of the pattern tree structure.
 886         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 887             let qpath = match pat.node {
 888                 PatKind::Path(ref qpath) |
 889                 PatKind::TupleStruct(ref qpath, ..) |
 890                 PatKind::Struct(ref qpath, ..) => qpath,
 891                 _ => return
 892             };
 893             let res = mc.tables.qpath_res(qpath, pat.hir_id);
 894             match res {
 895                 Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_did) => {
 896                     let variant_did = mc.tcx.parent(variant_ctor_did).unwrap();
 897                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 898
 899                     debug!("variantctor downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 900                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 901                 }
 902                 Res::Def(DefKind::Variant, variant_did) => {
 903                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 904
 905                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 906                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 907                 }
 908                 Res::Def(DefKind::Struct, _)
 909                 | Res::Def(DefKind::Ctor(..), _)
 910                 | Res::Def(DefKind::Union, _)
 911                 | Res::Def(DefKind::TyAlias, _)
 912                 | Res::Def(DefKind::AssocTy, _)
 913                 | Res::SelfTy(..) => {
 914                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 915                     delegate.matched_pat(pat, &cmt_pat, match_mode);
 916                 }
 917                 _ => {}
 918             }
 919         }));
 920     }
 921
 922     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 923         debug!("walk_captures({:?})", closure_expr);
 924
 925         let closure_def_id = self.tcx().hir().local_def_id_from_hir_id(closure_expr.hir_id);
 926         if let Some(upvars) = self.tcx().upvars(closure_def_id) {
 927             for upvar in upvars.iter() {
 928                 let var_hir_id = upvar.var_id();
 929                 let upvar_id = ty::UpvarId {
 930                     var_path: ty::UpvarPath { hir_id: var_hir_id },
 931                     closure_expr_id: closure_def_id.to_local(),
 932                 };
 933                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 934                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.hir_id,
 935                                                                    fn_decl_span,
 936                                                                    upvar));
 937                 match upvar_capture {
 938                     ty::UpvarCapture::ByValue => {
 939                         let mode = copy_or_move(&self.mc,
 940                                                 self.param_env,
 941                                                 &cmt_var,
 942                                                 CaptureMove);
 943                         self.delegate.consume(closure_expr.hir_id, upvar.span, &cmt_var, mode);
 944                     }
 945                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 946                         self.delegate.borrow(closure_expr.hir_id,
 947                                              fn_decl_span,
 948                                              &cmt_var,
 949                                              upvar_borrow.region,
 950                                              upvar_borrow.kind,
 951                                              ClosureCapture(upvar.span));
 952                     }
 953                 }
 954             }
 955         }
 956     }
 957
 958     fn cat_captured_var(&mut self,
 959                         closure_hir_id: hir::HirId,
 960                         closure_span: Span,
 961                         upvar: &hir::Upvar)
 962                         -> mc::McResult<mc::cmt_<'tcx>> {
 963         // Create the cmt for the variable being borrowed, from the
 964         // caller's perspective
 965         let var_hir_id = upvar.var_id();
 966         let var_ty = self.mc.node_ty(var_hir_id)?;
 967         self.mc.cat_res(closure_hir_id, closure_span, var_ty, upvar.res)
 968     }
 969 }
 970
 971 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 972                                 param_env: ty::ParamEnv<'tcx>,
 973                                 cmt: &mc::cmt_<'tcx>,
 974                                 move_reason: MoveReason)
 975                                 -> ConsumeMode
 976 {
 977     if !mc.type_is_copy_modulo_regions(param_env, cmt.ty, cmt.span) {
 978         Move(move_reason)
 979     } else {
 980         Copy
 981     }
 982 }