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