src/librustc_mir/hair/pattern/check_match.rs

   1 use super::_match::{MatchCheckCtxt, Matrix, expand_pattern, is_useful};
   2 use super::_match::Usefulness::*;
   3 use super::_match::WitnessPreference::*;
   4
   5 use super::{Pattern, PatternContext, PatternError, PatternKind};
   6
   7 use rustc::middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor};
   8 use rustc::middle::expr_use_visitor::{LoanCause, MutateMode};
   9 use rustc::middle::expr_use_visitor as euv;
  10 use rustc::middle::mem_categorization::cmt_;
  11 use rustc::middle::region;
  12 use rustc::session::Session;
  13 use rustc::ty::{self, Ty, TyCtxt};
  14 use rustc::ty::subst::{InternalSubsts, SubstsRef};
  15 use rustc::lint;
  16 use rustc_errors::{Applicability, DiagnosticBuilder};
  17
  18 use rustc::hir::def::*;
  19 use rustc::hir::def_id::DefId;
  20 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  21 use rustc::hir::{self, Pat, PatKind};
  22
  23 use smallvec::smallvec;
  24 use std::slice;
  25
  26 use syntax::ptr::P;
  27 use syntax_pos::{Span, DUMMY_SP, MultiSpan};
  28
  29 pub(crate) fn check_match<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
  30     let body_id = if let Some(id) = tcx.hir().as_local_hir_id(def_id) {
  31         tcx.hir().body_owned_by(id)
  32     } else {
  33         return;
  34     };
  35
  36     MatchVisitor {
  37         tcx,
  38         tables: tcx.body_tables(body_id),
  39         region_scope_tree: &tcx.region_scope_tree(def_id),
  40         param_env: tcx.param_env(def_id),
  41         identity_substs: InternalSubsts::identity_for_item(tcx, def_id),
  42     }.visit_body(tcx.hir().body(body_id));
  43 }
  44
  45 fn create_e0004<'a>(sess: &'a Session, sp: Span, error_message: String) -> DiagnosticBuilder<'a> {
  46     struct_span_err!(sess, sp, E0004, "{}", &error_message)
  47 }
  48
  49 struct MatchVisitor<'a, 'tcx: 'a> {
  50     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  51     tables: &'a ty::TypeckTables<'tcx>,
  52     param_env: ty::ParamEnv<'tcx>,
  53     identity_substs: SubstsRef<'tcx>,
  54     region_scope_tree: &'a region::ScopeTree,
  55 }
  56
  57 impl<'a, 'tcx> Visitor<'tcx> for MatchVisitor<'a, 'tcx> {
  58     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  59         NestedVisitorMap::None
  60     }
  61
  62     fn visit_expr(&mut self, ex: &'tcx hir::Expr) {
  63         intravisit::walk_expr(self, ex);
  64
  65         match ex.node {
  66             hir::ExprKind::Match(ref scrut, ref arms, source) => {
  67                 self.check_match(scrut, arms, source);
  68             }
  69             _ => {}
  70         }
  71     }
  72
  73     fn visit_local(&mut self, loc: &'tcx hir::Local) {
  74         intravisit::walk_local(self, loc);
  75
  76         self.check_irrefutable(&loc.pat, match loc.source {
  77             hir::LocalSource::Normal => "local binding",
  78             hir::LocalSource::ForLoopDesugar => "`for` loop binding",
  79             hir::LocalSource::AsyncFn => "async fn binding",
  80             hir::LocalSource::AwaitDesugar => "`await` future binding",
  81         });
  82
  83         // Check legality of move bindings and `@` patterns.
  84         self.check_patterns(false, slice::from_ref(&loc.pat));
  85     }
  86
  87     fn visit_body(&mut self, body: &'tcx hir::Body) {
  88         intravisit::walk_body(self, body);
  89
  90         for arg in &body.arguments {
  91             self.check_irrefutable(&arg.pat, "function argument");
  92             self.check_patterns(false, slice::from_ref(&arg.pat));
  93         }
  94     }
  95 }
  96
  97
  98 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
  99     fn report_inlining_errors(&self, pat_span: Span) {
 100         for error in &self.errors {
 101             match *error {
 102                 PatternError::StaticInPattern(span) => {
 103                     self.span_e0158(span, "statics cannot be referenced in patterns")
 104                 }
 105                 PatternError::AssociatedConstInPattern(span) => {
 106                     self.span_e0158(span, "associated consts cannot be referenced in patterns")
 107                 }
 108                 PatternError::FloatBug => {
 109                     // FIXME(#31407) this is only necessary because float parsing is buggy
 110                     ::rustc::mir::interpret::struct_error(
 111                         self.tcx.at(pat_span),
 112                         "could not evaluate float literal (see issue #31407)",
 113                     ).emit();
 114                 }
 115                 PatternError::NonConstPath(span) => {
 116                     ::rustc::mir::interpret::struct_error(
 117                         self.tcx.at(span),
 118                         "runtime values cannot be referenced in patterns",
 119                     ).emit();
 120                 }
 121             }
 122         }
 123     }
 124
 125     fn span_e0158(&self, span: Span, text: &str) {
 126         span_err!(self.tcx.sess, span, E0158, "{}", text)
 127     }
 128 }
 129
 130 impl<'a, 'tcx> MatchVisitor<'a, 'tcx> {
 131     fn check_patterns(&self, has_guard: bool, pats: &[P<Pat>]) {
 132         check_legality_of_move_bindings(self, has_guard, pats);
 133         for pat in pats {
 134             check_legality_of_bindings_in_at_patterns(self, pat);
 135         }
 136     }
 137
 138     fn check_match(
 139         &self,
 140         scrut: &hir::Expr,
 141         arms: &'tcx [hir::Arm],
 142         source: hir::MatchSource)
 143     {
 144         for arm in arms {
 145             // First, check legality of move bindings.
 146             self.check_patterns(arm.guard.is_some(), &arm.pats);
 147
 148             // Second, if there is a guard on each arm, make sure it isn't
 149             // assigning or borrowing anything mutably.
 150             if let Some(ref guard) = arm.guard {
 151                 if !self.tcx.features().bind_by_move_pattern_guards {
 152                     check_for_mutation_in_guard(self, &guard);
 153                 }
 154             }
 155
 156             // Third, perform some lints.
 157             for pat in &arm.pats {
 158                 check_for_bindings_named_same_as_variants(self, pat);
 159             }
 160         }
 161
 162         let module = self.tcx.hir().get_module_parent_by_hir_id(scrut.hir_id);
 163         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 164             let mut have_errors = false;
 165
 166             let inlined_arms : Vec<(Vec<_>, _)> = arms.iter().map(|arm| (
 167                 arm.pats.iter().map(|pat| {
 168                     let mut patcx = PatternContext::new(self.tcx,
 169                                                         self.param_env.and(self.identity_substs),
 170                                                         self.tables);
 171                     let pattern = expand_pattern(cx, patcx.lower_pattern(&pat));
 172                     if !patcx.errors.is_empty() {
 173                         patcx.report_inlining_errors(pat.span);
 174                         have_errors = true;
 175                     }
 176                     (pattern, &**pat)
 177                 }).collect(),
 178                 arm.guard.as_ref().map(|g| match g {
 179                     hir::Guard::If(ref e) => &**e,
 180                 })
 181             )).collect();
 182
 183             // Bail out early if inlining failed.
 184             if have_errors {
 185                 return;
 186             }
 187
 188             // Fourth, check for unreachable arms.
 189             check_arms(cx, &inlined_arms, source);
 190
 191             // Then, if the match has no arms, check whether the scrutinee
 192             // is uninhabited.
 193             let pat_ty = self.tables.node_type(scrut.hir_id);
 194             let module = self.tcx.hir().get_module_parent_by_hir_id(scrut.hir_id);
 195             let mut def_span = None;
 196             let mut missing_variants = vec![];
 197             if inlined_arms.is_empty() {
 198                 let scrutinee_is_uninhabited = if self.tcx.features().exhaustive_patterns {
 199                     self.tcx.is_ty_uninhabited_from(module, pat_ty)
 200                 } else {
 201                     match pat_ty.sty {
 202                         ty::Never => true,
 203                         ty::Adt(def, _) => {
 204                             def_span = self.tcx.hir().span_if_local(def.did);
 205                             if def.variants.len() < 4 && !def.variants.is_empty() {
 206                                 // keep around to point at the definition of non-covered variants
 207                                 missing_variants = def.variants.iter()
 208                                     .map(|variant| variant.ident)
 209                                     .collect();
 210                             }
 211
 212                             let is_non_exhaustive_and_non_local =
 213                                 def.is_variant_list_non_exhaustive() && !def.did.is_local();
 214
 215                             !(is_non_exhaustive_and_non_local) && def.variants.is_empty()
 216                         },
 217                         _ => false
 218                     }
 219                 };
 220                 if !scrutinee_is_uninhabited {
 221                     // We know the type is inhabited, so this must be wrong
 222                     let mut err = create_e0004(
 223                         self.tcx.sess,
 224                         scrut.span,
 225                         format!("non-exhaustive patterns: {}", match missing_variants.len() {
 226                             0 => format!("type `{}` is non-empty", pat_ty),
 227                             1 => format!(
 228                                 "pattern `{}` of type `{}` is not handled",
 229                                 missing_variants[0].name,
 230                                 pat_ty,
 231                             ),
 232                             _ => format!("multiple patterns of type `{}` are not handled", pat_ty),
 233                         }),
 234                     );
 235                     err.help("ensure that all possible cases are being handled, \
 236                               possibly by adding wildcards or more match arms");
 237                     if let Some(sp) = def_span {
 238                         err.span_label(sp, format!("`{}` defined here", pat_ty));
 239                     }
 240                     // point at the definition of non-covered enum variants
 241                     for variant in &missing_variants {
 242                         err.span_label(variant.span, "variant not covered");
 243                     }
 244                     err.emit();
 245                 }
 246                 // If the type *is* uninhabited, it's vacuously exhaustive
 247                 return;
 248             }
 249
 250             let matrix: Matrix<'_, '_> = inlined_arms
 251                 .iter()
 252                 .filter(|&&(_, guard)| guard.is_none())
 253                 .flat_map(|arm| &arm.0)
 254                 .map(|pat| smallvec![pat.0])
 255                 .collect();
 256             let scrut_ty = self.tables.node_type(scrut.hir_id);
 257             check_exhaustive(cx, scrut_ty, scrut.span, &matrix);
 258         })
 259     }
 260
 261     fn check_irrefutable(&self, pat: &'tcx Pat, origin: &str) {
 262         let module = self.tcx.hir().get_module_parent_by_hir_id(pat.hir_id);
 263         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 264             let mut patcx = PatternContext::new(self.tcx,
 265                                                 self.param_env.and(self.identity_substs),
 266                                                 self.tables);
 267             let pattern = patcx.lower_pattern(pat);
 268             let pattern_ty = pattern.ty;
 269             let pats: Matrix<'_, '_> = vec![smallvec![
 270                 expand_pattern(cx, pattern)
 271             ]].into_iter().collect();
 272
 273             let wild_pattern = Pattern {
 274                 ty: pattern_ty,
 275                 span: DUMMY_SP,
 276                 kind: box PatternKind::Wild,
 277             };
 278             let witness = match is_useful(cx, &pats, &[&wild_pattern], ConstructWitness) {
 279                 UsefulWithWitness(witness) => witness,
 280                 NotUseful => return,
 281                 Useful => bug!()
 282             };
 283
 284             let pattern_string = witness[0].single_pattern().to_string();
 285             let mut err = struct_span_err!(
 286                 self.tcx.sess, pat.span, E0005,
 287                 "refutable pattern in {}: `{}` not covered",
 288                 origin, pattern_string
 289             );
 290             let label_msg = match pat.node {
 291                 PatKind::Path(hir::QPath::Resolved(None, ref path))
 292                         if path.segments.len() == 1 && path.segments[0].args.is_none() => {
 293                     format!("interpreted as {} {} pattern, not new variable",
 294                             path.res.article(), path.res.descr())
 295                 }
 296                 _ => format!("pattern `{}` not covered", pattern_string),
 297             };
 298             err.span_label(pat.span, label_msg);
 299             if let ty::Adt(def, _) = pattern_ty.sty {
 300                 if let Some(sp) = self.tcx.hir().span_if_local(def.did){
 301                     err.span_label(sp, format!("`{}` defined here", pattern_ty));
 302                 }
 303             }
 304             err.emit();
 305         });
 306     }
 307 }
 308
 309 fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_>, pat: &Pat) {
 310     pat.walk(|p| {
 311         if let PatKind::Binding(_, _, ident, None) = p.node {
 312             if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 313                 if bm != ty::BindByValue(hir::MutImmutable) {
 314                     // Nothing to check.
 315                     return true;
 316                 }
 317                 let pat_ty = cx.tables.pat_ty(p);
 318                 if let ty::Adt(edef, _) = pat_ty.sty {
 319                     if edef.is_enum() && edef.variants.iter().any(|variant| {
 320                         variant.ident == ident && variant.ctor_kind == CtorKind::Const
 321                     }) {
 322                         let ty_path = cx.tcx.def_path_str(edef.did);
 323                         let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
 324                             "pattern binding `{}` is named the same as one \
 325                             of the variants of the type `{}`",
 326                             ident, ty_path);
 327                         err.span_suggestion(
 328                             p.span,
 329                             "to match on the variant, qualify the path",
 330                             format!("{}::{}", ty_path, ident),
 331                             Applicability::MachineApplicable
 332                         );
 333                         err.emit();
 334                     }
 335                 }
 336             } else {
 337                 cx.tcx.sess.delay_span_bug(p.span, "missing binding mode");
 338             }
 339         }
 340         true
 341     });
 342 }
 343
 344 /// Checks for common cases of "catchall" patterns that may not be intended as such.
 345 fn pat_is_catchall(pat: &Pat) -> bool {
 346     match pat.node {
 347         PatKind::Binding(.., None) => true,
 348         PatKind::Binding(.., Some(ref s)) => pat_is_catchall(s),
 349         PatKind::Ref(ref s, _) => pat_is_catchall(s),
 350         PatKind::Tuple(ref v, _) => v.iter().all(|p| {
 351             pat_is_catchall(&p)
 352         }),
 353         _ => false
 354     }
 355 }
 356
 357 // Check for unreachable patterns
 358 fn check_arms<'a, 'tcx>(
 359     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 360     arms: &[(Vec<(&'a Pattern<'tcx>, &hir::Pat)>, Option<&hir::Expr>)],
 361     source: hir::MatchSource,
 362 ) {
 363     let mut seen = Matrix::empty();
 364     let mut catchall = None;
 365     for (arm_index, &(ref pats, guard)) in arms.iter().enumerate() {
 366         for &(pat, hir_pat) in pats {
 367             let v = smallvec![pat];
 368
 369             match is_useful(cx, &seen, &v, LeaveOutWitness) {
 370                 NotUseful => {
 371                     match source {
 372                         hir::MatchSource::IfDesugar { .. } => bug!(),
 373                         hir::MatchSource::IfLetDesugar { .. } => {
 374                             cx.tcx.lint_hir(
 375                                 lint::builtin::IRREFUTABLE_LET_PATTERNS,
 376                                 hir_pat.hir_id,
 377                                 pat.span,
 378                                 "irrefutable if-let pattern",
 379                             );
 380                         }
 381
 382                         hir::MatchSource::WhileLetDesugar => {
 383                             // check which arm we're on.
 384                             match arm_index {
 385                                 // The arm with the user-specified pattern.
 386                                 0 => {
 387                                     cx.tcx.lint_hir(
 388                                         lint::builtin::UNREACHABLE_PATTERNS,
 389                                         hir_pat.hir_id, pat.span,
 390                                         "unreachable pattern");
 391                                 },
 392                                 // The arm with the wildcard pattern.
 393                                 1 => {
 394                                     cx.tcx.lint_hir(
 395                                         lint::builtin::IRREFUTABLE_LET_PATTERNS,
 396                                         hir_pat.hir_id,
 397                                         pat.span,
 398                                         "irrefutable while-let pattern",
 399                                     );
 400                                 },
 401                                 _ => bug!(),
 402                             }
 403                         }
 404
 405                         hir::MatchSource::ForLoopDesugar |
 406                         hir::MatchSource::Normal => {
 407                             let mut err = cx.tcx.struct_span_lint_hir(
 408                                 lint::builtin::UNREACHABLE_PATTERNS,
 409                                 hir_pat.hir_id,
 410                                 pat.span,
 411                                 "unreachable pattern",
 412                             );
 413                             // if we had a catchall pattern, hint at that
 414                             if let Some(catchall) = catchall {
 415                                 err.span_label(pat.span, "unreachable pattern");
 416                                 err.span_label(catchall, "matches any value");
 417                             }
 418                             err.emit();
 419                         }
 420
 421                         // Unreachable patterns in try and await expressions occur when one of
 422                         // the arms are an uninhabited type. Which is OK.
 423                         hir::MatchSource::AwaitDesugar |
 424                         hir::MatchSource::TryDesugar => {}
 425                     }
 426                 }
 427                 Useful => (),
 428                 UsefulWithWitness(_) => bug!()
 429             }
 430             if guard.is_none() {
 431                 seen.push(v);
 432                 if catchall.is_none() && pat_is_catchall(hir_pat) {
 433                     catchall = Some(pat.span);
 434                 }
 435             }
 436         }
 437     }
 438 }
 439
 440 fn check_exhaustive<'p, 'a: 'p, 'tcx: 'a>(
 441     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 442     scrut_ty: Ty<'tcx>,
 443     sp: Span,
 444     matrix: &Matrix<'p, 'tcx>,
 445 ) {
 446     let wild_pattern = Pattern {
 447         ty: scrut_ty,
 448         span: DUMMY_SP,
 449         kind: box PatternKind::Wild,
 450     };
 451     match is_useful(cx, matrix, &[&wild_pattern], ConstructWitness) {
 452         UsefulWithWitness(pats) => {
 453             let witnesses = if pats.is_empty() {
 454                 vec![&wild_pattern]
 455             } else {
 456                 pats.iter().map(|w| w.single_pattern()).collect()
 457             };
 458
 459             const LIMIT: usize = 3;
 460             let joined_patterns = match witnesses.len() {
 461                 0 => bug!(),
 462                 1 => format!("`{}`", witnesses[0]),
 463                 2..=LIMIT => {
 464                     let (tail, head) = witnesses.split_last().unwrap();
 465                     let head: Vec<_> = head.iter().map(|w| w.to_string()).collect();
 466                     format!("`{}` and `{}`", head.join("`, `"), tail)
 467                 }
 468                 _ => {
 469                     let (head, tail) = witnesses.split_at(LIMIT);
 470                     let head: Vec<_> = head.iter().map(|w| w.to_string()).collect();
 471                     format!("`{}` and {} more", head.join("`, `"), tail.len())
 472                 }
 473             };
 474
 475             let label_text = match witnesses.len() {
 476                 1 => format!("pattern {} not covered", joined_patterns),
 477                 _ => format!("patterns {} not covered", joined_patterns),
 478             };
 479             let mut err = create_e0004(cx.tcx.sess, sp, format!(
 480                 "non-exhaustive patterns: {} not covered",
 481                 joined_patterns,
 482             ));
 483             err.span_label(sp, label_text);
 484             // point at the definition of non-covered enum variants
 485             if let ty::Adt(def, _) = scrut_ty.sty {
 486                 if let Some(sp) = cx.tcx.hir().span_if_local(def.did){
 487                     err.span_label(sp, format!("`{}` defined here", scrut_ty));
 488                 }
 489             }
 490             let patterns = witnesses.iter().map(|p| (**p).clone()).collect::<Vec<Pattern<'_>>>();
 491             if patterns.len() < 4 {
 492                 for sp in maybe_point_at_variant(cx, scrut_ty, patterns.as_slice()) {
 493                     err.span_label(sp, "not covered");
 494                 }
 495             }
 496             err.help("ensure that all possible cases are being handled, \
 497                       possibly by adding wildcards or more match arms");
 498             err.emit();
 499         }
 500         NotUseful => {
 501             // This is good, wildcard pattern isn't reachable
 502         }
 503         _ => bug!()
 504     }
 505 }
 506
 507 fn maybe_point_at_variant(
 508     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 509     ty: Ty<'tcx>,
 510     patterns: &[Pattern<'_>],
 511 ) -> Vec<Span> {
 512     let mut covered = vec![];
 513     if let ty::Adt(def, _) = ty.sty {
 514         // Don't point at variants that have already been covered due to other patterns to avoid
 515         // visual clutter
 516         for pattern in patterns {
 517             let pk: &PatternKind<'_> = &pattern.kind;
 518             if let PatternKind::Variant { adt_def, variant_index, subpatterns, .. } = pk {
 519                 if adt_def.did == def.did {
 520                     let sp = def.variants[*variant_index].ident.span;
 521                     if covered.contains(&sp) {
 522                         continue;
 523                     }
 524                     covered.push(sp);
 525                     let subpatterns = subpatterns.iter()
 526                         .map(|field_pattern| field_pattern.pattern.clone())
 527                         .collect::<Vec<_>>();
 528                     covered.extend(
 529                         maybe_point_at_variant(cx, ty, subpatterns.as_slice()),
 530                     );
 531                 }
 532             }
 533             if let PatternKind::Leaf { subpatterns } = pk {
 534                 let subpatterns = subpatterns.iter()
 535                     .map(|field_pattern| field_pattern.pattern.clone())
 536                     .collect::<Vec<_>>();
 537                 covered.extend(maybe_point_at_variant(cx, ty, subpatterns.as_slice()));
 538             }
 539         }
 540     }
 541     covered
 542 }
 543
 544 // Legality of move bindings checking
 545 fn check_legality_of_move_bindings(
 546     cx: &MatchVisitor<'_, '_>,
 547     has_guard: bool,
 548     pats: &[P<Pat>],
 549 ) {
 550     let mut by_ref_span = None;
 551     for pat in pats {
 552         pat.each_binding(|_, hir_id, span, _path| {
 553             if let Some(&bm) = cx.tables.pat_binding_modes().get(hir_id) {
 554                 if let ty::BindByReference(..) = bm {
 555                     by_ref_span = Some(span);
 556                 }
 557             } else {
 558                 cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 559             }
 560         })
 561     }
 562     let span_vec = &mut Vec::new();
 563     let check_move = |p: &Pat, sub: Option<&Pat>, span_vec: &mut Vec<Span>| {
 564         // check legality of moving out of the enum
 565
 566         // x @ Foo(..) is legal, but x @ Foo(y) isn't.
 567         if sub.map_or(false, |p| p.contains_bindings()) {
 568             struct_span_err!(cx.tcx.sess, p.span, E0007,
 569                              "cannot bind by-move with sub-bindings")
 570                 .span_label(p.span, "binds an already bound by-move value by moving it")
 571                 .emit();
 572         } else if has_guard && !cx.tcx.features().bind_by_move_pattern_guards {
 573             let mut err = struct_span_err!(cx.tcx.sess, p.span, E0008,
 574                                            "cannot bind by-move into a pattern guard");
 575             err.span_label(p.span, "moves value into pattern guard");
 576             if cx.tcx.sess.opts.unstable_features.is_nightly_build() {
 577                 err.help("add #![feature(bind_by_move_pattern_guards)] to the \
 578                           crate attributes to enable");
 579             }
 580             err.emit();
 581         } else if let Some(_by_ref_span) = by_ref_span {
 582             span_vec.push(p.span);
 583         }
 584     };
 585
 586     for pat in pats {
 587         pat.walk(|p| {
 588             if let PatKind::Binding(_, _, _, ref sub) = p.node {
 589                 if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 590                     match bm {
 591                         ty::BindByValue(..) => {
 592                             let pat_ty = cx.tables.node_type(p.hir_id);
 593                             if !pat_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, pat.span) {
 594                                 check_move(p, sub.as_ref().map(|p| &**p), span_vec);
 595                             }
 596                         }
 597                         _ => {}
 598                     }
 599                 } else {
 600                     cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 601                 }
 602             }
 603             true
 604         });
 605     }
 606     if !span_vec.is_empty(){
 607         let span = MultiSpan::from_spans(span_vec.clone());
 608         let mut err = struct_span_err!(
 609             cx.tcx.sess,
 610             span,
 611             E0009,
 612             "cannot bind by-move and by-ref in the same pattern",
 613         );
 614         if let Some(by_ref_span) = by_ref_span {
 615             err.span_label(by_ref_span, "both by-ref and by-move used");
 616         }
 617         for span in span_vec.iter(){
 618             err.span_label(*span, "by-move pattern here");
 619         }
 620         err.emit();
 621     }
 622 }
 623
 624 /// Ensures that a pattern guard doesn't borrow by mutable reference or assign.
 625 //
 626 // FIXME: this should be done by borrowck.
 627 fn check_for_mutation_in_guard(cx: &MatchVisitor<'_, '_>, guard: &hir::Guard) {
 628     let mut checker = MutationChecker {
 629         cx,
 630     };
 631     match guard {
 632         hir::Guard::If(expr) =>
 633             ExprUseVisitor::new(&mut checker,
 634                                 cx.tcx,
 635                                 cx.param_env,
 636                                 cx.region_scope_tree,
 637                                 cx.tables,
 638                                 None).walk_expr(expr),
 639     };
 640 }
 641
 642 struct MutationChecker<'a, 'tcx: 'a> {
 643     cx: &'a MatchVisitor<'a, 'tcx>,
 644 }
 645
 646 impl<'a, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'tcx> {
 647     fn matched_pat(&mut self, _: &Pat, _: &cmt_<'_>, _: euv::MatchMode) {}
 648     fn consume(&mut self, _: hir::HirId, _: Span, _: &cmt_<'_>, _: ConsumeMode) {}
 649     fn consume_pat(&mut self, _: &Pat, _: &cmt_<'_>, _: ConsumeMode) {}
 650     fn borrow(&mut self,
 651               _: hir::HirId,
 652               span: Span,
 653               _: &cmt_<'_>,
 654               _: ty::Region<'tcx>,
 655               kind:ty:: BorrowKind,
 656               _: LoanCause) {
 657         match kind {
 658             ty::MutBorrow => {
 659                 let mut err = struct_span_err!(self.cx.tcx.sess, span, E0301,
 660                           "cannot mutably borrow in a pattern guard");
 661                 err.span_label(span, "borrowed mutably in pattern guard");
 662                 if self.cx.tcx.sess.opts.unstable_features.is_nightly_build() {
 663                     err.help("add #![feature(bind_by_move_pattern_guards)] to the \
 664                               crate attributes to enable");
 665                 }
 666                 err.emit();
 667             }
 668             ty::ImmBorrow | ty::UniqueImmBorrow => {}
 669         }
 670     }
 671     fn decl_without_init(&mut self, _: hir::HirId, _: Span) {}
 672     fn mutate(&mut self, _: hir::HirId, span: Span, _: &cmt_<'_>, mode: MutateMode) {
 673         match mode {
 674             MutateMode::JustWrite | MutateMode::WriteAndRead => {
 675                 struct_span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
 676                     .span_label(span, "assignment in pattern guard")
 677                     .emit();
 678             }
 679             MutateMode::Init => {}
 680         }
 681     }
 682 }
 683
 684 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
 685 /// because of the way rvalues are handled in the borrow check. (See issue
 686 /// #14587.)
 687 fn check_legality_of_bindings_in_at_patterns(cx: &MatchVisitor<'_, '_>, pat: &Pat) {
 688     AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
 689 }
 690
 691 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
 692     cx: &'a MatchVisitor<'b, 'tcx>,
 693     bindings_allowed: bool
 694 }
 695
 696 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
 697     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 698         NestedVisitorMap::None
 699     }
 700
 701     fn visit_pat(&mut self, pat: &Pat) {
 702         match pat.node {
 703             PatKind::Binding(.., ref subpat) => {
 704                 if !self.bindings_allowed {
 705                     struct_span_err!(self.cx.tcx.sess, pat.span, E0303,
 706                                      "pattern bindings are not allowed after an `@`")
 707                         .span_label(pat.span,  "not allowed after `@`")
 708                         .emit();
 709                 }
 710
 711                 if subpat.is_some() {
 712                     let bindings_were_allowed = self.bindings_allowed;
 713                     self.bindings_allowed = false;
 714                     intravisit::walk_pat(self, pat);
 715                     self.bindings_allowed = bindings_were_allowed;
 716                 }
 717             }
 718             _ => intravisit::walk_pat(self, pat),
 719         }
 720     }
 721 }