src/librustc/middle/expr_use_visitor.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A different sort of visitor for walking fn bodies.  Unlike the
  12 //! normal visitor, which just walks the entire body in one shot, the
  13 //! `ExprUseVisitor` determines how expressions are being used.
  14
  15 pub use self::LoanCause::*;
  16 pub use self::ConsumeMode::*;
  17 pub use self::MoveReason::*;
  18 pub use self::MatchMode::*;
  19 use self::TrackMatchMode::*;
  20 use self::OverloadedCallType::*;
  21
  22 use hir::def::Def;
  23 use hir::def_id::DefId;
  24 use infer::InferCtxt;
  25 use middle::mem_categorization as mc;
  26 use middle::region;
  27 use ty::{self, TyCtxt, adjustment};
  28
  29 use hir::{self, PatKind};
  30 use rustc_data_structures::sync::Lrc;
  31 use std::rc::Rc;
  32 use syntax::ast;
  33 use syntax::ptr::P;
  34 use syntax_pos::Span;
  35 use util::nodemap::ItemLocalSet;
  36
  37 ///////////////////////////////////////////////////////////////////////////
  38 // The Delegate trait
  39
  40 /// This trait defines the callbacks you can expect to receive when
  41 /// employing the ExprUseVisitor.
  42 pub trait Delegate<'tcx> {
  43     // The value found at `cmt` is either copied or moved, depending
  44     // on mode.
  45     fn consume(&mut self,
  46                consume_id: ast::NodeId,
  47                consume_span: Span,
  48                cmt: &mc::cmt_<'tcx>,
  49                mode: ConsumeMode);
  50
  51     // The value found at `cmt` has been determined to match the
  52     // pattern binding `matched_pat`, and its subparts are being
  53     // copied or moved depending on `mode`.  Note that `matched_pat`
  54     // is called on all variant/structs in the pattern (i.e., the
  55     // interior nodes of the pattern's tree structure) while
  56     // consume_pat is called on the binding identifiers in the pattern
  57     // (which are leaves of the pattern's tree structure).
  58     //
  59     // Note that variants/structs and identifiers are disjoint; thus
  60     // `matched_pat` and `consume_pat` are never both called on the
  61     // same input pattern structure (though of `consume_pat` can be
  62     // called on a subpart of an input passed to `matched_pat).
  63     fn matched_pat(&mut self,
  64                    matched_pat: &hir::Pat,
  65                    cmt: &mc::cmt_<'tcx>,
  66                    mode: MatchMode);
  67
  68     // The value found at `cmt` is either copied or moved via the
  69     // pattern binding `consume_pat`, depending on mode.
  70     fn consume_pat(&mut self,
  71                    consume_pat: &hir::Pat,
  72                    cmt: &mc::cmt_<'tcx>,
  73                    mode: ConsumeMode);
  74
  75     // The value found at `borrow` is being borrowed at the point
  76     // `borrow_id` for the region `loan_region` with kind `bk`.
  77     fn borrow(&mut self,
  78               borrow_id: ast::NodeId,
  79               borrow_span: Span,
  80               cmt: &mc::cmt_<'tcx>,
  81               loan_region: ty::Region<'tcx>,
  82               bk: ty::BorrowKind,
  83               loan_cause: LoanCause);
  84
  85     // The local variable `id` is declared but not initialized.
  86     fn decl_without_init(&mut self,
  87                          id: ast::NodeId,
  88                          span: Span);
  89
  90     // The path at `cmt` is being assigned to.
  91     fn mutate(&mut self,
  92               assignment_id: ast::NodeId,
  93               assignment_span: Span,
  94               assignee_cmt: &mc::cmt_<'tcx>,
  95               mode: MutateMode);
  96 }
  97
  98 #[derive(Copy, Clone, PartialEq, Debug)]
  99 pub enum LoanCause {
 100     ClosureCapture(Span),
 101     AddrOf,
 102     AutoRef,
 103     AutoUnsafe,
 104     RefBinding,
 105     OverloadedOperator,
 106     ClosureInvocation,
 107     ForLoop,
 108     MatchDiscriminant
 109 }
 110
 111 #[derive(Copy, Clone, PartialEq, Debug)]
 112 pub enum ConsumeMode {
 113     Copy,                // reference to x where x has a type that copies
 114     Move(MoveReason),    // reference to x where x has a type that moves
 115 }
 116
 117 #[derive(Copy, Clone, PartialEq, Debug)]
 118 pub enum MoveReason {
 119     DirectRefMove,
 120     PatBindingMove,
 121     CaptureMove,
 122 }
 123
 124 #[derive(Copy, Clone, PartialEq, Debug)]
 125 pub enum MatchMode {
 126     NonBindingMatch,
 127     BorrowingMatch,
 128     CopyingMatch,
 129     MovingMatch,
 130 }
 131
 132 #[derive(Copy, Clone, PartialEq, Debug)]
 133 enum TrackMatchMode {
 134     Unknown,
 135     Definite(MatchMode),
 136     Conflicting,
 137 }
 138
 139 impl TrackMatchMode {
 140     // Builds up the whole match mode for a pattern from its constituent
 141     // parts.  The lattice looks like this:
 142     //
 143     //          Conflicting
 144     //            /     \
 145     //           /       \
 146     //      Borrowing   Moving
 147     //           \       /
 148     //            \     /
 149     //            Copying
 150     //               |
 151     //          NonBinding
 152     //               |
 153     //            Unknown
 154     //
 155     // examples:
 156     //
 157     // * `(_, some_int)` pattern is Copying, since
 158     //   NonBinding + Copying => Copying
 159     //
 160     // * `(some_int, some_box)` pattern is Moving, since
 161     //   Copying + Moving => Moving
 162     //
 163     // * `(ref x, some_box)` pattern is Conflicting, since
 164     //   Borrowing + Moving => Conflicting
 165     //
 166     // Note that the `Unknown` and `Conflicting` states are
 167     // represented separately from the other more interesting
 168     // `Definite` states, which simplifies logic here somewhat.
 169     fn lub(&mut self, mode: MatchMode) {
 170         *self = match (*self, mode) {
 171             // Note that clause order below is very significant.
 172             (Unknown, new) => Definite(new),
 173             (Definite(old), new) if old == new => Definite(old),
 174
 175             (Definite(old), NonBindingMatch) => Definite(old),
 176             (Definite(NonBindingMatch), new) => Definite(new),
 177
 178             (Definite(old), CopyingMatch) => Definite(old),
 179             (Definite(CopyingMatch), new) => Definite(new),
 180
 181             (Definite(_), _) => Conflicting,
 182             (Conflicting, _) => *self,
 183         };
 184     }
 185
 186     fn match_mode(&self) -> MatchMode {
 187         match *self {
 188             Unknown => NonBindingMatch,
 189             Definite(mode) => mode,
 190             Conflicting => {
 191                 // Conservatively return MovingMatch to let the
 192                 // compiler continue to make progress.
 193                 MovingMatch
 194             }
 195         }
 196     }
 197 }
 198
 199 #[derive(Copy, Clone, PartialEq, Debug)]
 200 pub enum MutateMode {
 201     Init,
 202     JustWrite,    // x = y
 203     WriteAndRead, // x += y
 204 }
 205
 206 #[derive(Copy, Clone)]
 207 enum OverloadedCallType {
 208     FnOverloadedCall,
 209     FnMutOverloadedCall,
 210     FnOnceOverloadedCall,
 211 }
 212
 213 impl OverloadedCallType {
 214     fn from_trait_id(tcx: TyCtxt<'_, '_, '_>, trait_id: DefId) -> OverloadedCallType {
 215         for &(maybe_function_trait, overloaded_call_type) in &[
 216             (tcx.lang_items().fn_once_trait(), FnOnceOverloadedCall),
 217             (tcx.lang_items().fn_mut_trait(), FnMutOverloadedCall),
 218             (tcx.lang_items().fn_trait(), FnOverloadedCall)
 219         ] {
 220             match maybe_function_trait {
 221                 Some(function_trait) if function_trait == trait_id => {
 222                     return overloaded_call_type
 223                 }
 224                 _ => continue,
 225             }
 226         }
 227
 228         bug!("overloaded call didn't map to known function trait")
 229     }
 230
 231     fn from_method_id(tcx: TyCtxt<'_, '_, '_>, method_id: DefId) -> OverloadedCallType {
 232         let method = tcx.associated_item(method_id);
 233         OverloadedCallType::from_trait_id(tcx, method.container.id())
 234     }
 235 }
 236
 237 ///////////////////////////////////////////////////////////////////////////
 238 // The ExprUseVisitor type
 239 //
 240 // This is the code that actually walks the tree.
 241 pub struct ExprUseVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 242     mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 243     delegate: &'a mut dyn Delegate<'tcx>,
 244     param_env: ty::ParamEnv<'tcx>,
 245 }
 246
 247 // If the MC results in an error, it's because the type check
 248 // failed (or will fail, when the error is uncovered and reported
 249 // during writeback). In this case, we just ignore this part of the
 250 // code.
 251 //
 252 // Note that this macro appears similar to try!(), but, unlike try!(),
 253 // it does not propagate the error.
 254 macro_rules! return_if_err {
 255     ($inp: expr) => (
 256         match $inp {
 257             Ok(v) => v,
 258             Err(()) => {
 259                 debug!("mc reported err");
 260                 return
 261             }
 262         }
 263     )
 264 }
 265
 266 impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx, 'tcx> {
 267     /// Creates the ExprUseVisitor, configuring it with the various options provided:
 268     ///
 269     /// - `delegate` -- who receives the callbacks
 270     /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
 271     /// - `region_scope_tree` --- region scope tree for the code being analyzed
 272     /// - `tables` --- typeck results for the code being analyzed
 273     /// - `rvalue_promotable_map` --- if you care about rvalue promotion, then provide
 274     ///   the map here (it can be computed with `tcx.rvalue_promotable_map(def_id)`).
 275     ///   `None` means that rvalues will be given more conservative lifetimes.
 276     ///
 277     /// See also `with_infer`, which is used *during* typeck.
 278     pub fn new(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 279                tcx: TyCtxt<'a, 'tcx, 'tcx>,
 280                param_env: ty::ParamEnv<'tcx>,
 281                region_scope_tree: &'a region::ScopeTree,
 282                tables: &'a ty::TypeckTables<'tcx>,
 283                rvalue_promotable_map: Option<Lrc<ItemLocalSet>>)
 284                -> Self
 285     {
 286         ExprUseVisitor {
 287             mc: mc::MemCategorizationContext::new(tcx,
 288                                                   region_scope_tree,
 289                                                   tables,
 290                                                   rvalue_promotable_map),
 291             delegate,
 292             param_env,
 293         }
 294     }
 295 }
 296
 297 impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
 298     pub fn with_infer(delegate: &'a mut (dyn Delegate<'tcx>+'a),
 299                       infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 300                       param_env: ty::ParamEnv<'tcx>,
 301                       region_scope_tree: &'a region::ScopeTree,
 302                       tables: &'a ty::TypeckTables<'tcx>)
 303                       -> Self
 304     {
 305         ExprUseVisitor {
 306             mc: mc::MemCategorizationContext::with_infer(infcx, region_scope_tree, tables),
 307             delegate,
 308             param_env,
 309         }
 310     }
 311
 312     pub fn consume_body(&mut self, body: &hir::Body) {
 313         debug!("consume_body(body={:?})", body);
 314
 315         for arg in &body.arguments {
 316             let arg_ty = return_if_err!(self.mc.pat_ty_adjusted(&arg.pat));
 317             debug!("consume_body: arg_ty = {:?}", arg_ty);
 318
 319             let fn_body_scope_r =
 320                 self.tcx().mk_region(ty::ReScope(
 321                     region::Scope {
 322                         id: body.value.hir_id.local_id,
 323                         data: region::ScopeData::Node
 324                 }));
 325             let arg_cmt = Rc::new(self.mc.cat_rvalue(
 326                 arg.hir_id,
 327                 arg.pat.span,
 328                 fn_body_scope_r, // Args live only as long as the fn body.
 329                 arg_ty));
 330
 331             self.walk_irrefutable_pat(arg_cmt, &arg.pat);
 332         }
 333
 334         self.consume_expr(&body.value);
 335     }
 336
 337     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 338         self.mc.tcx
 339     }
 340
 341     fn delegate_consume(&mut self,
 342                         consume_id: ast::NodeId,
 343                         consume_span: Span,
 344                         cmt: &mc::cmt_<'tcx>) {
 345         debug!("delegate_consume(consume_id={}, cmt={:?})",
 346                consume_id, cmt);
 347
 348         let mode = copy_or_move(&self.mc, self.param_env, cmt, DirectRefMove);
 349         self.delegate.consume(consume_id, consume_span, cmt, mode);
 350     }
 351
 352     fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
 353         for expr in exprs {
 354             self.consume_expr(&expr);
 355         }
 356     }
 357
 358     pub fn consume_expr(&mut self, expr: &hir::Expr) {
 359         debug!("consume_expr(expr={:?})", expr);
 360
 361         let cmt = return_if_err!(self.mc.cat_expr(expr));
 362         self.delegate_consume(expr.id, expr.span, &cmt);
 363         self.walk_expr(expr);
 364     }
 365
 366     fn mutate_expr(&mut self,
 367                    span: Span,
 368                    assignment_expr: &hir::Expr,
 369                    expr: &hir::Expr,
 370                    mode: MutateMode) {
 371         let cmt = return_if_err!(self.mc.cat_expr(expr));
 372         self.delegate.mutate(assignment_expr.id, span, &cmt, mode);
 373         self.walk_expr(expr);
 374     }
 375
 376     fn borrow_expr(&mut self,
 377                    expr: &hir::Expr,
 378                    r: ty::Region<'tcx>,
 379                    bk: ty::BorrowKind,
 380                    cause: LoanCause) {
 381         debug!("borrow_expr(expr={:?}, r={:?}, bk={:?})",
 382                expr, r, bk);
 383
 384         let cmt = return_if_err!(self.mc.cat_expr(expr));
 385         self.delegate.borrow(expr.id, expr.span, &cmt, r, bk, cause);
 386
 387         self.walk_expr(expr)
 388     }
 389
 390     fn select_from_expr(&mut self, expr: &hir::Expr) {
 391         self.walk_expr(expr)
 392     }
 393
 394     pub fn walk_expr(&mut self, expr: &hir::Expr) {
 395         debug!("walk_expr(expr={:?})", expr);
 396
 397         self.walk_adjustment(expr);
 398
 399         match expr.node {
 400             hir::ExprKind::Path(_) => { }
 401
 402             hir::ExprKind::Type(ref subexpr, _) => {
 403                 self.walk_expr(&subexpr)
 404             }
 405
 406             hir::ExprKind::Unary(hir::UnDeref, ref base) => { // *base
 407                 self.select_from_expr(&base);
 408             }
 409
 410             hir::ExprKind::Field(ref base, _) => { // base.f
 411                 self.select_from_expr(&base);
 412             }
 413
 414             hir::ExprKind::Index(ref lhs, ref rhs) => { // lhs[rhs]
 415                 self.select_from_expr(&lhs);
 416                 self.consume_expr(&rhs);
 417             }
 418
 419             hir::ExprKind::Call(ref callee, ref args) => { // callee(args)
 420                 self.walk_callee(expr, &callee);
 421                 self.consume_exprs(args);
 422             }
 423
 424             hir::ExprKind::MethodCall(.., ref args) => { // callee.m(args)
 425                 self.consume_exprs(args);
 426             }
 427
 428             hir::ExprKind::Struct(_, ref fields, ref opt_with) => {
 429                 self.walk_struct_expr(fields, opt_with);
 430             }
 431
 432             hir::ExprKind::Tup(ref exprs) => {
 433                 self.consume_exprs(exprs);
 434             }
 435
 436             hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => {
 437                 self.consume_expr(&cond_expr);
 438                 self.walk_expr(&then_expr);
 439                 if let Some(ref else_expr) = *opt_else_expr {
 440                     self.consume_expr(&else_expr);
 441                 }
 442             }
 443
 444             hir::ExprKind::Match(ref discr, ref arms, _) => {
 445                 let discr_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&discr)));
 446                 let r = self.tcx().types.re_empty;
 447                 self.borrow_expr(&discr, r, ty::ImmBorrow, MatchDiscriminant);
 448
 449                 // treatment of the discriminant is handled while walking the arms.
 450                 for arm in arms {
 451                     let mode = self.arm_move_mode(discr_cmt.clone(), arm);
 452                     let mode = mode.match_mode();
 453                     self.walk_arm(discr_cmt.clone(), arm, mode);
 454                 }
 455             }
 456
 457             hir::ExprKind::Array(ref exprs) => {
 458                 self.consume_exprs(exprs);
 459             }
 460
 461             hir::ExprKind::AddrOf(m, ref base) => {   // &base
 462                 // make sure that the thing we are pointing out stays valid
 463                 // for the lifetime `scope_r` of the resulting ptr:
 464                 let expr_ty = return_if_err!(self.mc.expr_ty(expr));
 465                 if let ty::Ref(r, _, _) = expr_ty.sty {
 466                     let bk = ty::BorrowKind::from_mutbl(m);
 467                     self.borrow_expr(&base, r, bk, AddrOf);
 468                 }
 469             }
 470
 471             hir::ExprKind::InlineAsm(ref ia, ref outputs, ref inputs) => {
 472                 for (o, output) in ia.outputs.iter().zip(outputs) {
 473                     if o.is_indirect {
 474                         self.consume_expr(output);
 475                     } else {
 476                         self.mutate_expr(
 477                             output.span,
 478                             expr,
 479                             output,
 480                             if o.is_rw {
 481                                 MutateMode::WriteAndRead
 482                             } else {
 483                                 MutateMode::JustWrite
 484                             },
 485                         );
 486                     }
 487                 }
 488                 self.consume_exprs(inputs);
 489             }
 490
 491             hir::ExprKind::Continue(..) |
 492             hir::ExprKind::Lit(..) => {}
 493
 494             hir::ExprKind::Loop(ref blk, _, _) => {
 495                 self.walk_block(&blk);
 496             }
 497
 498             hir::ExprKind::While(ref cond_expr, ref blk, _) => {
 499                 self.consume_expr(&cond_expr);
 500                 self.walk_block(&blk);
 501             }
 502
 503             hir::ExprKind::Unary(_, ref lhs) => {
 504                 self.consume_expr(&lhs);
 505             }
 506
 507             hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
 508                 self.consume_expr(&lhs);
 509                 self.consume_expr(&rhs);
 510             }
 511
 512             hir::ExprKind::Block(ref blk, _) => {
 513                 self.walk_block(&blk);
 514             }
 515
 516             hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
 517                 if let Some(ref expr) = *opt_expr {
 518                     self.consume_expr(&expr);
 519                 }
 520             }
 521
 522             hir::ExprKind::Assign(ref lhs, ref rhs) => {
 523                 self.mutate_expr(expr.span, expr, &lhs, MutateMode::JustWrite);
 524                 self.consume_expr(&rhs);
 525             }
 526
 527             hir::ExprKind::Cast(ref base, _) => {
 528                 self.consume_expr(&base);
 529             }
 530
 531             hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
 532                 if self.mc.tables.is_method_call(expr) {
 533                     self.consume_expr(lhs);
 534                 } else {
 535                     self.mutate_expr(expr.span, expr, &lhs, MutateMode::WriteAndRead);
 536                 }
 537                 self.consume_expr(&rhs);
 538             }
 539
 540             hir::ExprKind::Repeat(ref base, _) => {
 541                 self.consume_expr(&base);
 542             }
 543
 544             hir::ExprKind::Closure(.., fn_decl_span, _) => {
 545                 self.walk_captures(expr, fn_decl_span)
 546             }
 547
 548             hir::ExprKind::Box(ref base) => {
 549                 self.consume_expr(&base);
 550             }
 551
 552             hir::ExprKind::Yield(ref value) => {
 553                 self.consume_expr(&value);
 554             }
 555         }
 556     }
 557
 558     fn walk_callee(&mut self, call: &hir::Expr, callee: &hir::Expr) {
 559         let callee_ty = return_if_err!(self.mc.expr_ty_adjusted(callee));
 560         debug!("walk_callee: callee={:?} callee_ty={:?}",
 561                callee, callee_ty);
 562         match callee_ty.sty {
 563             ty::FnDef(..) | ty::FnPtr(_) => {
 564                 self.consume_expr(callee);
 565             }
 566             ty::Error => { }
 567             _ => {
 568                 if let Some(def) = self.mc.tables.type_dependent_defs().get(call.hir_id) {
 569                     let def_id = def.def_id();
 570                     let call_scope = region::Scope {
 571                         id: call.hir_id.local_id,
 572                         data: region::ScopeData::Node
 573                     };
 574                     match OverloadedCallType::from_method_id(self.tcx(), def_id) {
 575                         FnMutOverloadedCall => {
 576                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 577                             self.borrow_expr(callee,
 578                                             call_scope_r,
 579                                             ty::MutBorrow,
 580                                             ClosureInvocation);
 581                         }
 582                         FnOverloadedCall => {
 583                             let call_scope_r = self.tcx().mk_region(ty::ReScope(call_scope));
 584                             self.borrow_expr(callee,
 585                                             call_scope_r,
 586                                             ty::ImmBorrow,
 587                                             ClosureInvocation);
 588                         }
 589                         FnOnceOverloadedCall => self.consume_expr(callee),
 590                     }
 591                 } else {
 592                     self.tcx().sess.delay_span_bug(call.span,
 593                                                    "no type-dependent def for overloaded call");
 594                 }
 595             }
 596         }
 597     }
 598
 599     fn walk_stmt(&mut self, stmt: &hir::Stmt) {
 600         match stmt.node {
 601             hir::StmtKind::Decl(ref decl, _) => {
 602                 match decl.node {
 603                     hir::DeclKind::Local(ref local) => {
 604                         self.walk_local(&local);
 605                     }
 606
 607                     hir::DeclKind::Item(_) => {
 608                         // we don't visit nested items in this visitor,
 609                         // only the fn body we were given.
 610                     }
 611                 }
 612             }
 613
 614             hir::StmtKind::Expr(ref expr, _) |
 615             hir::StmtKind::Semi(ref expr, _) => {
 616                 self.consume_expr(&expr);
 617             }
 618         }
 619     }
 620
 621     fn walk_local(&mut self, local: &hir::Local) {
 622         match local.init {
 623             None => {
 624                 local.pat.each_binding(|_, hir_id, span, _| {
 625                     let node_id = self.mc.tcx.hir.hir_to_node_id(hir_id);
 626                     self.delegate.decl_without_init(node_id, span);
 627                 })
 628             }
 629
 630             Some(ref expr) => {
 631                 // Variable declarations with
 632                 // initializers are considered
 633                 // "assigns", which is handled by
 634                 // `walk_pat`:
 635                 self.walk_expr(&expr);
 636                 let init_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&expr)));
 637                 self.walk_irrefutable_pat(init_cmt, &local.pat);
 638             }
 639         }
 640     }
 641
 642     /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
 643     /// depending on its type.
 644     fn walk_block(&mut self, blk: &hir::Block) {
 645         debug!("walk_block(blk.id={})", blk.id);
 646
 647         for stmt in &blk.stmts {
 648             self.walk_stmt(stmt);
 649         }
 650
 651         if let Some(ref tail_expr) = blk.expr {
 652             self.consume_expr(&tail_expr);
 653         }
 654     }
 655
 656     fn walk_struct_expr(&mut self,
 657                         fields: &[hir::Field],
 658                         opt_with: &Option<P<hir::Expr>>) {
 659         // Consume the expressions supplying values for each field.
 660         for field in fields {
 661             self.consume_expr(&field.expr);
 662         }
 663
 664         let with_expr = match *opt_with {
 665             Some(ref w) => &**w,
 666             None => { return; }
 667         };
 668
 669         let with_cmt = Rc::new(return_if_err!(self.mc.cat_expr(&with_expr)));
 670
 671         // Select just those fields of the `with`
 672         // expression that will actually be used
 673         match with_cmt.ty.sty {
 674             ty::Adt(adt, substs) if adt.is_struct() => {
 675                 // Consume those fields of the with expression that are needed.
 676                 for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() {
 677                     let is_mentioned = fields.iter().any(|f| {
 678                         self.tcx().field_index(f.id, self.mc.tables) == f_index
 679                     });
 680                     if !is_mentioned {
 681                         let cmt_field = self.mc.cat_field(
 682                             &*with_expr,
 683                             with_cmt.clone(),
 684                             f_index,
 685                             with_field.ident,
 686                             with_field.ty(self.tcx(), substs)
 687                         );
 688                         self.delegate_consume(with_expr.id, with_expr.span, &cmt_field);
 689                     }
 690                 }
 691             }
 692             _ => {
 693                 // the base expression should always evaluate to a
 694                 // struct; however, when EUV is run during typeck, it
 695                 // may not. This will generate an error earlier in typeck,
 696                 // so we can just ignore it.
 697                 if !self.tcx().sess.has_errors() {
 698                     span_bug!(
 699                         with_expr.span,
 700                         "with expression doesn't evaluate to a struct");
 701                 }
 702             }
 703         }
 704
 705         // walk the with expression so that complex expressions
 706         // are properly handled.
 707         self.walk_expr(with_expr);
 708     }
 709
 710     // Invoke the appropriate delegate calls for anything that gets
 711     // consumed or borrowed as part of the automatic adjustment
 712     // process.
 713     fn walk_adjustment(&mut self, expr: &hir::Expr) {
 714         let adjustments = self.mc.tables.expr_adjustments(expr);
 715         let mut cmt = return_if_err!(self.mc.cat_expr_unadjusted(expr));
 716         for adjustment in adjustments {
 717             debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
 718             match adjustment.kind {
 719                 adjustment::Adjust::NeverToAny |
 720                 adjustment::Adjust::ReifyFnPointer |
 721                 adjustment::Adjust::UnsafeFnPointer |
 722                 adjustment::Adjust::ClosureFnPointer |
 723                 adjustment::Adjust::MutToConstPointer |
 724                 adjustment::Adjust::Unsize => {
 725                     // Creating a closure/fn-pointer or unsizing consumes
 726                     // the input and stores it into the resulting rvalue.
 727                     self.delegate_consume(expr.id, expr.span, &cmt);
 728                 }
 729
 730                 adjustment::Adjust::Deref(None) => {}
 731
 732                 // Autoderefs for overloaded Deref calls in fact reference
 733                 // their receiver. That is, if we have `(*x)` where `x`
 734                 // is of type `Rc<T>`, then this in fact is equivalent to
 735                 // `x.deref()`. Since `deref()` is declared with `&self`,
 736                 // this is an autoref of `x`.
 737                 adjustment::Adjust::Deref(Some(ref deref)) => {
 738                     let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
 739                     self.delegate.borrow(expr.id, expr.span, &cmt, deref.region, bk, AutoRef);
 740                 }
 741
 742                 adjustment::Adjust::Borrow(ref autoref) => {
 743                     self.walk_autoref(expr, &cmt, autoref);
 744                 }
 745             }
 746             cmt = return_if_err!(self.mc.cat_expr_adjusted(expr, cmt, &adjustment));
 747         }
 748     }
 749
 750     /// Walks the autoref `autoref` applied to the autoderef'd
 751     /// `expr`. `cmt_base` is the mem-categorized form of `expr`
 752     /// after all relevant autoderefs have occurred.
 753     fn walk_autoref(&mut self,
 754                     expr: &hir::Expr,
 755                     cmt_base: &mc::cmt_<'tcx>,
 756                     autoref: &adjustment::AutoBorrow<'tcx>) {
 757         debug!("walk_autoref(expr.id={} cmt_base={:?} autoref={:?})",
 758                expr.id,
 759                cmt_base,
 760                autoref);
 761
 762         match *autoref {
 763             adjustment::AutoBorrow::Ref(r, m) => {
 764                 self.delegate.borrow(expr.id,
 765                                      expr.span,
 766                                      cmt_base,
 767                                      r,
 768                                      ty::BorrowKind::from_mutbl(m.into()),
 769                                      AutoRef);
 770             }
 771
 772             adjustment::AutoBorrow::RawPtr(m) => {
 773                 debug!("walk_autoref: expr.id={} cmt_base={:?}",
 774                        expr.id,
 775                        cmt_base);
 776
 777                 // Converting from a &T to *T (or &mut T to *mut T) is
 778                 // treated as borrowing it for the enclosing temporary
 779                 // scope.
 780                 let r = self.tcx().mk_region(ty::ReScope(
 781                     region::Scope {
 782                         id: expr.hir_id.local_id,
 783                         data: region::ScopeData::Node
 784                     }));
 785
 786                 self.delegate.borrow(expr.id,
 787                                      expr.span,
 788                                      cmt_base,
 789                                      r,
 790                                      ty::BorrowKind::from_mutbl(m),
 791                                      AutoUnsafe);
 792             }
 793         }
 794     }
 795
 796     fn arm_move_mode(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm) -> TrackMatchMode {
 797         let mut mode = Unknown;
 798         for pat in &arm.pats {
 799             self.determine_pat_move_mode(discr_cmt.clone(), &pat, &mut mode);
 800         }
 801         mode
 802     }
 803
 804     fn walk_arm(&mut self, discr_cmt: mc::cmt<'tcx>, arm: &hir::Arm, mode: MatchMode) {
 805         for pat in &arm.pats {
 806             self.walk_pat(discr_cmt.clone(), &pat, mode);
 807         }
 808
 809         if let Some(hir::Guard::If(ref e)) = arm.guard {
 810             self.consume_expr(e)
 811         }
 812
 813         self.consume_expr(&arm.body);
 814     }
 815
 816     /// Walks a pat that occurs in isolation (i.e. top-level of fn
 817     /// arg or let binding.  *Not* a match arm or nested pat.)
 818     fn walk_irrefutable_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat) {
 819         let mut mode = Unknown;
 820         self.determine_pat_move_mode(cmt_discr.clone(), pat, &mut mode);
 821         let mode = mode.match_mode();
 822         self.walk_pat(cmt_discr, pat, mode);
 823     }
 824
 825     /// Identifies any bindings within `pat` and accumulates within
 826     /// `mode` whether the overall pattern/match structure is a move,
 827     /// copy, or borrow.
 828     fn determine_pat_move_mode(&mut self,
 829                                cmt_discr: mc::cmt<'tcx>,
 830                                pat: &hir::Pat,
 831                                mode: &mut TrackMatchMode) {
 832         debug!("determine_pat_move_mode cmt_discr={:?} pat={:?}", cmt_discr, pat);
 833
 834         return_if_err!(self.mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 835             if let PatKind::Binding(..) = pat.node {
 836                 let bm = *self.mc.tables.pat_binding_modes()
 837                                         .get(pat.hir_id)
 838                                         .expect("missing binding mode");
 839                 match bm {
 840                     ty::BindByReference(..) =>
 841                         mode.lub(BorrowingMatch),
 842                     ty::BindByValue(..) => {
 843                         match copy_or_move(&self.mc, self.param_env, &cmt_pat, PatBindingMove) {
 844                             Copy => mode.lub(CopyingMatch),
 845                             Move(..) => mode.lub(MovingMatch),
 846                         }
 847                     }
 848                 }
 849             }
 850         }));
 851     }
 852
 853     /// The core driver for walking a pattern; `match_mode` must be
 854     /// established up front, e.g. via `determine_pat_move_mode` (see
 855     /// also `walk_irrefutable_pat` for patterns that stand alone).
 856     fn walk_pat(&mut self, cmt_discr: mc::cmt<'tcx>, pat: &hir::Pat, match_mode: MatchMode) {
 857         debug!("walk_pat(cmt_discr={:?}, pat={:?})", cmt_discr, pat);
 858
 859         let tcx = self.tcx();
 860         let ExprUseVisitor { ref mc, ref mut delegate, param_env } = *self;
 861         return_if_err!(mc.cat_pattern(cmt_discr.clone(), pat, |cmt_pat, pat| {
 862             if let PatKind::Binding(_, canonical_id, ..) = pat.node {
 863                 debug!(
 864                     "walk_pat: binding cmt_pat={:?} pat={:?} match_mode={:?}",
 865                     cmt_pat,
 866                     pat,
 867                     match_mode,
 868                 );
 869                 if let Some(&bm) = mc.tables.pat_binding_modes().get(pat.hir_id) {
 870                     debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
 871
 872                     // pat_ty: the type of the binding being produced.
 873                     let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
 874                     debug!("walk_pat: pat_ty={:?}", pat_ty);
 875
 876                     // Each match binding is effectively an assignment to the
 877                     // binding being produced.
 878                     let def = Def::Local(canonical_id);
 879                     if let Ok(ref binding_cmt) = mc.cat_def(pat.hir_id, pat.span, pat_ty, def) {
 880                         delegate.mutate(pat.id, pat.span, binding_cmt, MutateMode::Init);
 881                     }
 882
 883                     // It is also a borrow or copy/move of the value being matched.
 884                     match bm {
 885                         ty::BindByReference(m) => {
 886                             if let ty::Ref(r, _, _) = pat_ty.sty {
 887                                 let bk = ty::BorrowKind::from_mutbl(m);
 888                                 delegate.borrow(pat.id, pat.span, &cmt_pat, r, bk, RefBinding);
 889                             }
 890                         }
 891                         ty::BindByValue(..) => {
 892                             let mode = copy_or_move(mc, param_env, &cmt_pat, PatBindingMove);
 893                             debug!("walk_pat binding consuming pat");
 894                             delegate.consume_pat(pat, &cmt_pat, mode);
 895                         }
 896                     }
 897                 } else {
 898                     tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 899                 }
 900             }
 901         }));
 902
 903         // Do a second pass over the pattern, calling `matched_pat` on
 904         // the interior nodes (enum variants and structs), as opposed
 905         // to the above loop's visit of than the bindings that form
 906         // the leaves of the pattern tree structure.
 907         return_if_err!(mc.cat_pattern(cmt_discr, pat, |cmt_pat, pat| {
 908             let qpath = match pat.node {
 909                 PatKind::Path(ref qpath) |
 910                 PatKind::TupleStruct(ref qpath, ..) |
 911                 PatKind::Struct(ref qpath, ..) => qpath,
 912                 _ => return
 913             };
 914             let def = mc.tables.qpath_def(qpath, pat.hir_id);
 915             match def {
 916                 Def::Variant(variant_did) |
 917                 Def::VariantCtor(variant_did, ..) => {
 918                     let downcast_cmt = mc.cat_downcast_if_needed(pat, cmt_pat, variant_did);
 919
 920                     debug!("variant downcast_cmt={:?} pat={:?}", downcast_cmt, pat);
 921                     delegate.matched_pat(pat, &downcast_cmt, match_mode);
 922                 }
 923                 Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 924                 Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 925                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
 926                     delegate.matched_pat(pat, &cmt_pat, match_mode);
 927                 }
 928                 _ => {}
 929             }
 930         }));
 931     }
 932
 933     fn walk_captures(&mut self, closure_expr: &hir::Expr, fn_decl_span: Span) {
 934         debug!("walk_captures({:?})", closure_expr);
 935
 936         self.tcx().with_freevars(closure_expr.id, |freevars| {
 937             for freevar in freevars {
 938                 let var_hir_id = self.tcx().hir.node_to_hir_id(freevar.var_id());
 939                 let closure_def_id = self.tcx().hir.local_def_id(closure_expr.id);
 940                 let upvar_id = ty::UpvarId {
 941                     var_id: var_hir_id,
 942                     closure_expr_id: closure_def_id.to_local(),
 943                 };
 944                 let upvar_capture = self.mc.tables.upvar_capture(upvar_id);
 945                 let cmt_var = return_if_err!(self.cat_captured_var(closure_expr.hir_id,
 946                                                                    fn_decl_span,
 947                                                                    freevar));
 948                 match upvar_capture {
 949                     ty::UpvarCapture::ByValue => {
 950                         let mode = copy_or_move(&self.mc,
 951                                                 self.param_env,
 952                                                 &cmt_var,
 953                                                 CaptureMove);
 954                         self.delegate.consume(closure_expr.id, freevar.span, &cmt_var, mode);
 955                     }
 956                     ty::UpvarCapture::ByRef(upvar_borrow) => {
 957                         self.delegate.borrow(closure_expr.id,
 958                                              fn_decl_span,
 959                                              &cmt_var,
 960                                              upvar_borrow.region,
 961                                              upvar_borrow.kind,
 962                                              ClosureCapture(freevar.span));
 963                     }
 964                 }
 965             }
 966         });
 967     }
 968
 969     fn cat_captured_var(&mut self,
 970                         closure_hir_id: hir::HirId,
 971                         closure_span: Span,
 972                         upvar: &hir::Freevar)
 973                         -> mc::McResult<mc::cmt_<'tcx>> {
 974         // Create the cmt for the variable being borrowed, from the
 975         // caller's perspective
 976         let var_hir_id = self.tcx().hir.node_to_hir_id(upvar.var_id());
 977         let var_ty = self.mc.node_ty(var_hir_id)?;
 978         self.mc.cat_def(closure_hir_id, closure_span, var_ty, upvar.def)
 979     }
 980 }
 981
 982 fn copy_or_move<'a, 'gcx, 'tcx>(mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
 983                                 param_env: ty::ParamEnv<'tcx>,
 984                                 cmt: &mc::cmt_<'tcx>,
 985                                 move_reason: MoveReason)
 986                                 -> ConsumeMode
 987 {
 988     if mc.type_moves_by_default(param_env, cmt.ty, cmt.span) {
 989         Move(move_reason)
 990     } else {
 991         Copy
 992     }
 993 }