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         body_owner: def_id,
  39         tables: tcx.body_tables(body_id),
  40         region_scope_tree: &tcx.region_scope_tree(def_id),
  41         param_env: tcx.param_env(def_id),
  42         identity_substs: InternalSubsts::identity_for_item(tcx, def_id),
  43     }.visit_body(tcx.hir().body(body_id));
  44 }
  45
  46 fn create_e0004<'a>(sess: &'a Session, sp: Span, error_message: String) -> DiagnosticBuilder<'a> {
  47     struct_span_err!(sess, sp, E0004, "{}", &error_message)
  48 }
  49
  50 struct MatchVisitor<'a, 'tcx: 'a> {
  51     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  52     body_owner: DefId,
  53     tables: &'a ty::TypeckTables<'tcx>,
  54     param_env: ty::ParamEnv<'tcx>,
  55     identity_substs: SubstsRef<'tcx>,
  56     region_scope_tree: &'a region::ScopeTree,
  57 }
  58
  59 impl<'a, 'tcx> Visitor<'tcx> for MatchVisitor<'a, 'tcx> {
  60     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  61         NestedVisitorMap::None
  62     }
  63
  64     fn visit_expr(&mut self, ex: &'tcx hir::Expr) {
  65         intravisit::walk_expr(self, ex);
  66
  67         match ex.node {
  68             hir::ExprKind::Match(ref scrut, ref arms, source) => {
  69                 self.check_match(scrut, arms, source);
  70             }
  71             _ => {}
  72         }
  73     }
  74
  75     fn visit_local(&mut self, loc: &'tcx hir::Local) {
  76         intravisit::walk_local(self, loc);
  77
  78         self.check_irrefutable(&loc.pat, match loc.source {
  79             hir::LocalSource::Normal => "local binding",
  80             hir::LocalSource::ForLoopDesugar => "`for` loop binding",
  81             hir::LocalSource::AsyncFn => "async fn binding",
  82             hir::LocalSource::AwaitDesugar => "`await` future binding",
  83         });
  84
  85         // Check legality of move bindings and `@` patterns.
  86         self.check_patterns(false, slice::from_ref(&loc.pat));
  87     }
  88
  89     fn visit_body(&mut self, body: &'tcx hir::Body) {
  90         intravisit::walk_body(self, body);
  91
  92         for arg in &body.arguments {
  93             self.check_irrefutable(&arg.pat, "function argument");
  94             self.check_patterns(false, slice::from_ref(&arg.pat));
  95         }
  96     }
  97 }
  98
  99
 100 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 101     fn report_inlining_errors(&self, pat_span: Span) {
 102         for error in &self.errors {
 103             match *error {
 104                 PatternError::StaticInPattern(span) => {
 105                     self.span_e0158(span, "statics cannot be referenced in patterns")
 106                 }
 107                 PatternError::AssocConstInPattern(span) => {
 108                     self.span_e0158(span, "associated consts cannot be referenced in patterns")
 109                 }
 110                 PatternError::FloatBug => {
 111                     // FIXME(#31407) this is only necessary because float parsing is buggy
 112                     ::rustc::mir::interpret::struct_error(
 113                         self.tcx.at(pat_span),
 114                         "could not evaluate float literal (see issue #31407)",
 115                     ).emit();
 116                 }
 117                 PatternError::NonConstPath(span) => {
 118                     ::rustc::mir::interpret::struct_error(
 119                         self.tcx.at(span),
 120                         "runtime values cannot be referenced in patterns",
 121                     ).emit();
 122                 }
 123             }
 124         }
 125     }
 126
 127     fn span_e0158(&self, span: Span, text: &str) {
 128         span_err!(self.tcx.sess, span, E0158, "{}", text)
 129     }
 130 }
 131
 132 impl<'a, 'tcx> MatchVisitor<'a, 'tcx> {
 133     fn check_patterns(&self, has_guard: bool, pats: &[P<Pat>]) {
 134         check_legality_of_move_bindings(self, has_guard, pats);
 135         for pat in pats {
 136             check_legality_of_bindings_in_at_patterns(self, pat);
 137         }
 138     }
 139
 140     fn check_match(
 141         &self,
 142         scrut: &hir::Expr,
 143         arms: &'tcx [hir::Arm],
 144         source: hir::MatchSource)
 145     {
 146         for arm in arms {
 147             // First, check legality of move bindings.
 148             self.check_patterns(arm.guard.is_some(), &arm.pats);
 149
 150             // Second, if there is a guard on each arm, make sure it isn't
 151             // assigning or borrowing anything mutably.
 152             if let Some(ref guard) = arm.guard {
 153                 if !self.tcx.features().bind_by_move_pattern_guards {
 154                     check_for_mutation_in_guard(self, &guard);
 155                 }
 156             }
 157
 158             // Third, perform some lints.
 159             for pat in &arm.pats {
 160                 check_for_bindings_named_same_as_variants(self, pat);
 161             }
 162         }
 163
 164         let module = self.tcx.hir().get_module_parent_by_hir_id(scrut.hir_id);
 165         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 166             let mut have_errors = false;
 167
 168             let inlined_arms : Vec<(Vec<_>, _)> = arms.iter().map(|arm| (
 169                 arm.pats.iter().map(|pat| {
 170                     let mut patcx = PatternContext::new(self.tcx,
 171                                                         self.param_env.and(self.identity_substs),
 172                                                         self.tables);
 173                     let pattern = expand_pattern(cx, patcx.lower_pattern(&pat));
 174                     if !patcx.errors.is_empty() {
 175                         patcx.report_inlining_errors(pat.span);
 176                         have_errors = true;
 177                     }
 178                     (pattern, &**pat)
 179                 }).collect(),
 180                 arm.guard.as_ref().map(|g| match g {
 181                     hir::Guard::If(ref e) => &**e,
 182                 })
 183             )).collect();
 184
 185             // Bail out early if inlining failed.
 186             if have_errors {
 187                 return;
 188             }
 189
 190             // Fourth, check for unreachable arms.
 191             check_arms(cx, &inlined_arms, source);
 192
 193             // Then, if the match has no arms, check whether the scrutinee
 194             // is uninhabited.
 195             let pat_ty = self.tables.node_type(scrut.hir_id);
 196             let module = self.tcx.hir().get_module_parent_by_hir_id(scrut.hir_id);
 197             let mut def_span = None;
 198             let mut missing_variants = vec![];
 199             if inlined_arms.is_empty() {
 200                 let scrutinee_is_uninhabited = if self.tcx.features().exhaustive_patterns {
 201                     self.tcx.is_ty_uninhabited_from(module, pat_ty)
 202                 } else {
 203                     match pat_ty.sty {
 204                         ty::Never => true,
 205                         ty::Adt(def, _) => {
 206                             def_span = self.tcx.hir().span_if_local(def.did);
 207                             if def.variants.len() < 4 && !def.variants.is_empty() {
 208                                 // keep around to point at the definition of non-covered variants
 209                                 missing_variants = def.variants.iter()
 210                                     .map(|variant| variant.ident)
 211                                     .collect();
 212                             }
 213
 214                             let is_non_exhaustive_and_non_local =
 215                                 def.is_variant_list_non_exhaustive() && !def.did.is_local();
 216
 217                             !(is_non_exhaustive_and_non_local) && def.variants.is_empty()
 218                         },
 219                         _ => false
 220                     }
 221                 };
 222                 if !scrutinee_is_uninhabited {
 223                     // We know the type is inhabited, so this must be wrong
 224                     let mut err = create_e0004(
 225                         self.tcx.sess,
 226                         scrut.span,
 227                         format!("non-exhaustive patterns: {}", match missing_variants.len() {
 228                             0 => format!("type `{}` is non-empty", pat_ty),
 229                             1 => format!(
 230                                 "pattern `{}` of type `{}` is not handled",
 231                                 missing_variants[0].name,
 232                                 pat_ty,
 233                             ),
 234                             _ => format!("multiple patterns of type `{}` are not handled", pat_ty),
 235                         }),
 236                     );
 237                     err.help("ensure that all possible cases are being handled, \
 238                               possibly by adding wildcards or more match arms");
 239                     if let Some(sp) = def_span {
 240                         err.span_label(sp, format!("`{}` defined here", pat_ty));
 241                     }
 242                     // point at the definition of non-covered enum variants
 243                     for variant in &missing_variants {
 244                         err.span_label(variant.span, "variant not covered");
 245                     }
 246                     err.emit();
 247                 }
 248                 // If the type *is* uninhabited, it's vacuously exhaustive
 249                 return;
 250             }
 251
 252             let matrix: Matrix<'_, '_> = inlined_arms
 253                 .iter()
 254                 .filter(|&&(_, guard)| guard.is_none())
 255                 .flat_map(|arm| &arm.0)
 256                 .map(|pat| smallvec![pat.0])
 257                 .collect();
 258             let scrut_ty = self.tables.node_type(scrut.hir_id);
 259             check_exhaustive(cx, scrut_ty, scrut.span, &matrix);
 260         })
 261     }
 262
 263     fn check_irrefutable(&self, pat: &'tcx Pat, origin: &str) {
 264         let module = self.tcx.hir().get_module_parent_by_hir_id(pat.hir_id);
 265         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 266             let mut patcx = PatternContext::new(self.tcx,
 267                                                 self.param_env.and(self.identity_substs),
 268                                                 self.tables);
 269             let pattern = patcx.lower_pattern(pat);
 270             let pattern_ty = pattern.ty;
 271             let pats: Matrix<'_, '_> = vec![smallvec![
 272                 expand_pattern(cx, pattern)
 273             ]].into_iter().collect();
 274
 275             let wild_pattern = Pattern {
 276                 ty: pattern_ty,
 277                 span: DUMMY_SP,
 278                 kind: box PatternKind::Wild,
 279             };
 280             let witness = match is_useful(cx, &pats, &[&wild_pattern], ConstructWitness) {
 281                 UsefulWithWitness(witness) => witness,
 282                 NotUseful => return,
 283                 Useful => bug!()
 284             };
 285
 286             let pattern_string = witness[0].single_pattern().to_string();
 287             let mut err = struct_span_err!(
 288                 self.tcx.sess, pat.span, E0005,
 289                 "refutable pattern in {}: `{}` not covered",
 290                 origin, pattern_string
 291             );
 292             let label_msg = match pat.node {
 293                 PatKind::Path(hir::QPath::Resolved(None, ref path))
 294                         if path.segments.len() == 1 && path.segments[0].args.is_none() => {
 295                     format!("interpreted as {} {} pattern, not new variable",
 296                             path.res.article(), path.res.descr())
 297                 }
 298                 _ => format!("pattern `{}` not covered", pattern_string),
 299             };
 300             err.span_label(pat.span, label_msg);
 301             if let ty::Adt(def, _) = pattern_ty.sty {
 302                 if let Some(sp) = self.tcx.hir().span_if_local(def.did){
 303                     err.span_label(sp, format!("`{}` defined here", pattern_ty));
 304                 }
 305             }
 306             err.emit();
 307         });
 308     }
 309 }
 310
 311 fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_>, pat: &Pat) {
 312     pat.walk(|p| {
 313         if let PatKind::Binding(_, _, ident, None) = p.node {
 314             if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 315                 if bm != ty::BindByValue(hir::MutImmutable) {
 316                     // Nothing to check.
 317                     return true;
 318                 }
 319                 let pat_ty = cx.tables.pat_ty(p);
 320                 if let ty::Adt(edef, _) = pat_ty.sty {
 321                     if edef.is_enum() && edef.variants.iter().any(|variant| {
 322                         variant.ident == ident && variant.ctor_kind == CtorKind::Const
 323                     }) {
 324                         let ty_path = cx.tcx.def_path_str(edef.did);
 325                         let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
 326                             "pattern binding `{}` is named the same as one \
 327                             of the variants of the type `{}`",
 328                             ident, ty_path);
 329                         err.span_suggestion(
 330                             p.span,
 331                             "to match on the variant, qualify the path",
 332                             format!("{}::{}", ty_path, ident),
 333                             Applicability::MachineApplicable
 334                         );
 335                         err.emit();
 336                     }
 337                 }
 338             } else {
 339                 cx.tcx.sess.delay_span_bug(p.span, "missing binding mode");
 340             }
 341         }
 342         true
 343     });
 344 }
 345
 346 /// Checks for common cases of "catchall" patterns that may not be intended as such.
 347 fn pat_is_catchall(pat: &Pat) -> bool {
 348     match pat.node {
 349         PatKind::Binding(.., None) => true,
 350         PatKind::Binding(.., Some(ref s)) => pat_is_catchall(s),
 351         PatKind::Ref(ref s, _) => pat_is_catchall(s),
 352         PatKind::Tuple(ref v, _) => v.iter().all(|p| {
 353             pat_is_catchall(&p)
 354         }),
 355         _ => false
 356     }
 357 }
 358
 359 // Check for unreachable patterns
 360 fn check_arms<'a, 'tcx>(
 361     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 362     arms: &[(Vec<(&'a Pattern<'tcx>, &hir::Pat)>, Option<&hir::Expr>)],
 363     source: hir::MatchSource,
 364 ) {
 365     let mut seen = Matrix::empty();
 366     let mut catchall = None;
 367     for (arm_index, &(ref pats, guard)) in arms.iter().enumerate() {
 368         for &(pat, hir_pat) in pats {
 369             let v = smallvec![pat];
 370
 371             match is_useful(cx, &seen, &v, LeaveOutWitness) {
 372                 NotUseful => {
 373                     match source {
 374                         hir::MatchSource::IfDesugar { .. } => bug!(),
 375                         hir::MatchSource::IfLetDesugar { .. } => {
 376                             cx.tcx.lint_hir(
 377                                 lint::builtin::IRREFUTABLE_LET_PATTERNS,
 378                                 hir_pat.hir_id,
 379                                 pat.span,
 380                                 "irrefutable if-let pattern",
 381                             );
 382                         }
 383
 384                         hir::MatchSource::WhileLetDesugar => {
 385                             // check which arm we're on.
 386                             match arm_index {
 387                                 // The arm with the user-specified pattern.
 388                                 0 => {
 389                                     cx.tcx.lint_hir(
 390                                         lint::builtin::UNREACHABLE_PATTERNS,
 391                                         hir_pat.hir_id, pat.span,
 392                                         "unreachable pattern");
 393                                 },
 394                                 // The arm with the wildcard pattern.
 395                                 1 => {
 396                                     cx.tcx.lint_hir(
 397                                         lint::builtin::IRREFUTABLE_LET_PATTERNS,
 398                                         hir_pat.hir_id,
 399                                         pat.span,
 400                                         "irrefutable while-let pattern",
 401                                     );
 402                                 },
 403                                 _ => bug!(),
 404                             }
 405                         }
 406
 407                         hir::MatchSource::ForLoopDesugar |
 408                         hir::MatchSource::Normal => {
 409                             let mut err = cx.tcx.struct_span_lint_hir(
 410                                 lint::builtin::UNREACHABLE_PATTERNS,
 411                                 hir_pat.hir_id,
 412                                 pat.span,
 413                                 "unreachable pattern",
 414                             );
 415                             // if we had a catchall pattern, hint at that
 416                             if let Some(catchall) = catchall {
 417                                 err.span_label(pat.span, "unreachable pattern");
 418                                 err.span_label(catchall, "matches any value");
 419                             }
 420                             err.emit();
 421                         }
 422
 423                         // Unreachable patterns in try and await expressions occur when one of
 424                         // the arms are an uninhabited type. Which is OK.
 425                         hir::MatchSource::AwaitDesugar |
 426                         hir::MatchSource::TryDesugar => {}
 427                     }
 428                 }
 429                 Useful => (),
 430                 UsefulWithWitness(_) => bug!()
 431             }
 432             if guard.is_none() {
 433                 seen.push(v);
 434                 if catchall.is_none() && pat_is_catchall(hir_pat) {
 435                     catchall = Some(pat.span);
 436                 }
 437             }
 438         }
 439     }
 440 }
 441
 442 fn check_exhaustive<'p, 'a: 'p, 'tcx: 'a>(
 443     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 444     scrut_ty: Ty<'tcx>,
 445     sp: Span,
 446     matrix: &Matrix<'p, 'tcx>,
 447 ) {
 448     let wild_pattern = Pattern {
 449         ty: scrut_ty,
 450         span: DUMMY_SP,
 451         kind: box PatternKind::Wild,
 452     };
 453     match is_useful(cx, matrix, &[&wild_pattern], ConstructWitness) {
 454         UsefulWithWitness(pats) => {
 455             let witnesses = if pats.is_empty() {
 456                 vec![&wild_pattern]
 457             } else {
 458                 pats.iter().map(|w| w.single_pattern()).collect()
 459             };
 460
 461             const LIMIT: usize = 3;
 462             let joined_patterns = match witnesses.len() {
 463                 0 => bug!(),
 464                 1 => format!("`{}`", witnesses[0]),
 465                 2..=LIMIT => {
 466                     let (tail, head) = witnesses.split_last().unwrap();
 467                     let head: Vec<_> = head.iter().map(|w| w.to_string()).collect();
 468                     format!("`{}` and `{}`", head.join("`, `"), tail)
 469                 }
 470                 _ => {
 471                     let (head, tail) = witnesses.split_at(LIMIT);
 472                     let head: Vec<_> = head.iter().map(|w| w.to_string()).collect();
 473                     format!("`{}` and {} more", head.join("`, `"), tail.len())
 474                 }
 475             };
 476
 477             let label_text = match witnesses.len() {
 478                 1 => format!("pattern {} not covered", joined_patterns),
 479                 _ => format!("patterns {} not covered", joined_patterns),
 480             };
 481             let mut err = create_e0004(cx.tcx.sess, sp, format!(
 482                 "non-exhaustive patterns: {} not covered",
 483                 joined_patterns,
 484             ));
 485             err.span_label(sp, label_text);
 486             // point at the definition of non-covered enum variants
 487             if let ty::Adt(def, _) = scrut_ty.sty {
 488                 if let Some(sp) = cx.tcx.hir().span_if_local(def.did){
 489                     err.span_label(sp, format!("`{}` defined here", scrut_ty));
 490                 }
 491             }
 492             let patterns = witnesses.iter().map(|p| (**p).clone()).collect::<Vec<Pattern<'_>>>();
 493             if patterns.len() < 4 {
 494                 for sp in maybe_point_at_variant(cx, scrut_ty, patterns.as_slice()) {
 495                     err.span_label(sp, "not covered");
 496                 }
 497             }
 498             err.help("ensure that all possible cases are being handled, \
 499                       possibly by adding wildcards or more match arms");
 500             err.emit();
 501         }
 502         NotUseful => {
 503             // This is good, wildcard pattern isn't reachable
 504         }
 505         _ => bug!()
 506     }
 507 }
 508
 509 fn maybe_point_at_variant(
 510     cx: &mut MatchCheckCtxt<'a, 'tcx>,
 511     ty: Ty<'tcx>,
 512     patterns: &[Pattern<'_>],
 513 ) -> Vec<Span> {
 514     let mut covered = vec![];
 515     if let ty::Adt(def, _) = ty.sty {
 516         // Don't point at variants that have already been covered due to other patterns to avoid
 517         // visual clutter
 518         for pattern in patterns {
 519             let pk: &PatternKind<'_> = &pattern.kind;
 520             if let PatternKind::Variant { adt_def, variant_index, subpatterns, .. } = pk {
 521                 if adt_def.did == def.did {
 522                     let sp = def.variants[*variant_index].ident.span;
 523                     if covered.contains(&sp) {
 524                         continue;
 525                     }
 526                     covered.push(sp);
 527                     let subpatterns = subpatterns.iter()
 528                         .map(|field_pattern| field_pattern.pattern.clone())
 529                         .collect::<Vec<_>>();
 530                     covered.extend(
 531                         maybe_point_at_variant(cx, ty, subpatterns.as_slice()),
 532                     );
 533                 }
 534             }
 535             if let PatternKind::Leaf { subpatterns } = pk {
 536                 let subpatterns = subpatterns.iter()
 537                     .map(|field_pattern| field_pattern.pattern.clone())
 538                     .collect::<Vec<_>>();
 539                 covered.extend(maybe_point_at_variant(cx, ty, subpatterns.as_slice()));
 540             }
 541         }
 542     }
 543     covered
 544 }
 545
 546 // Legality of move bindings checking
 547 fn check_legality_of_move_bindings(
 548     cx: &MatchVisitor<'_, '_>,
 549     has_guard: bool,
 550     pats: &[P<Pat>],
 551 ) {
 552     let mut by_ref_span = None;
 553     for pat in pats {
 554         pat.each_binding(|_, hir_id, span, _path| {
 555             if let Some(&bm) = cx.tables.pat_binding_modes().get(hir_id) {
 556                 if let ty::BindByReference(..) = bm {
 557                     by_ref_span = Some(span);
 558                 }
 559             } else {
 560                 cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 561             }
 562         })
 563     }
 564     let span_vec = &mut Vec::new();
 565     let check_move = |p: &Pat, sub: Option<&Pat>, span_vec: &mut Vec<Span>| {
 566         // check legality of moving out of the enum
 567
 568         // x @ Foo(..) is legal, but x @ Foo(y) isn't.
 569         if sub.map_or(false, |p| p.contains_bindings()) {
 570             struct_span_err!(cx.tcx.sess, p.span, E0007,
 571                              "cannot bind by-move with sub-bindings")
 572                 .span_label(p.span, "binds an already bound by-move value by moving it")
 573                 .emit();
 574         } else if has_guard && !cx.tcx.features().bind_by_move_pattern_guards {
 575             let mut err = struct_span_err!(cx.tcx.sess, p.span, E0008,
 576                                            "cannot bind by-move into a pattern guard");
 577             err.span_label(p.span, "moves value into pattern guard");
 578             if cx.tcx.sess.opts.unstable_features.is_nightly_build() {
 579                 err.help("add #![feature(bind_by_move_pattern_guards)] to the \
 580                           crate attributes to enable");
 581             }
 582             err.emit();
 583         } else if let Some(_by_ref_span) = by_ref_span {
 584             span_vec.push(p.span);
 585         }
 586     };
 587
 588     for pat in pats {
 589         pat.walk(|p| {
 590             if let PatKind::Binding(_, _, _, ref sub) = p.node {
 591                 if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 592                     match bm {
 593                         ty::BindByValue(..) => {
 594                             let pat_ty = cx.tables.node_type(p.hir_id);
 595                             if !pat_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, pat.span) {
 596                                 check_move(p, sub.as_ref().map(|p| &**p), span_vec);
 597                             }
 598                         }
 599                         _ => {}
 600                     }
 601                 } else {
 602                     cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 603                 }
 604             }
 605             true
 606         });
 607     }
 608     if !span_vec.is_empty(){
 609         let span = MultiSpan::from_spans(span_vec.clone());
 610         let mut err = struct_span_err!(
 611             cx.tcx.sess,
 612             span,
 613             E0009,
 614             "cannot bind by-move and by-ref in the same pattern",
 615         );
 616         if let Some(by_ref_span) = by_ref_span {
 617             err.span_label(by_ref_span, "both by-ref and by-move used");
 618         }
 619         for span in span_vec.iter(){
 620             err.span_label(*span, "by-move pattern here");
 621         }
 622         err.emit();
 623     }
 624 }
 625
 626 /// Ensures that a pattern guard doesn't borrow by mutable reference or assign.
 627 //
 628 // FIXME: this should be done by borrowck.
 629 fn check_for_mutation_in_guard(cx: &MatchVisitor<'_, '_>, guard: &hir::Guard) {
 630     let mut checker = MutationChecker {
 631         cx,
 632     };
 633     match guard {
 634         hir::Guard::If(expr) =>
 635             ExprUseVisitor::new(&mut checker,
 636                                 cx.tcx,
 637                                 cx.body_owner,
 638                                 cx.param_env,
 639                                 cx.region_scope_tree,
 640                                 cx.tables,
 641                                 None).walk_expr(expr),
 642     };
 643 }
 644
 645 struct MutationChecker<'a, 'tcx: 'a> {
 646     cx: &'a MatchVisitor<'a, 'tcx>,
 647 }
 648
 649 impl<'a, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'tcx> {
 650     fn matched_pat(&mut self, _: &Pat, _: &cmt_<'_>, _: euv::MatchMode) {}
 651     fn consume(&mut self, _: hir::HirId, _: Span, _: &cmt_<'_>, _: ConsumeMode) {}
 652     fn consume_pat(&mut self, _: &Pat, _: &cmt_<'_>, _: ConsumeMode) {}
 653     fn borrow(&mut self,
 654               _: hir::HirId,
 655               span: Span,
 656               _: &cmt_<'_>,
 657               _: ty::Region<'tcx>,
 658               kind:ty:: BorrowKind,
 659               _: LoanCause) {
 660         match kind {
 661             ty::MutBorrow => {
 662                 let mut err = struct_span_err!(self.cx.tcx.sess, span, E0301,
 663                           "cannot mutably borrow in a pattern guard");
 664                 err.span_label(span, "borrowed mutably in pattern guard");
 665                 if self.cx.tcx.sess.opts.unstable_features.is_nightly_build() {
 666                     err.help("add #![feature(bind_by_move_pattern_guards)] to the \
 667                               crate attributes to enable");
 668                 }
 669                 err.emit();
 670             }
 671             ty::ImmBorrow | ty::UniqueImmBorrow => {}
 672         }
 673     }
 674     fn decl_without_init(&mut self, _: hir::HirId, _: Span) {}
 675     fn mutate(&mut self, _: hir::HirId, span: Span, _: &cmt_<'_>, mode: MutateMode) {
 676         match mode {
 677             MutateMode::JustWrite | MutateMode::WriteAndRead => {
 678                 struct_span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
 679                     .span_label(span, "assignment in pattern guard")
 680                     .emit();
 681             }
 682             MutateMode::Init => {}
 683         }
 684     }
 685 }
 686
 687 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
 688 /// because of the way rvalues are handled in the borrow check. (See issue
 689 /// #14587.)
 690 fn check_legality_of_bindings_in_at_patterns(cx: &MatchVisitor<'_, '_>, pat: &Pat) {
 691     AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
 692 }
 693
 694 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
 695     cx: &'a MatchVisitor<'b, 'tcx>,
 696     bindings_allowed: bool
 697 }
 698
 699 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
 700     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 701         NestedVisitorMap::None
 702     }
 703
 704     fn visit_pat(&mut self, pat: &Pat) {
 705         match pat.node {
 706             PatKind::Binding(.., ref subpat) => {
 707                 if !self.bindings_allowed {
 708                     struct_span_err!(self.cx.tcx.sess, pat.span, E0303,
 709                                      "pattern bindings are not allowed after an `@`")
 710                         .span_label(pat.span,  "not allowed after `@`")
 711                         .emit();
 712                 }
 713
 714                 if subpat.is_some() {
 715                     let bindings_were_allowed = self.bindings_allowed;
 716                     self.bindings_allowed = false;
 717                     intravisit::walk_pat(self, pat);
 718                     self.bindings_allowed = bindings_were_allowed;
 719                 }
 720             }
 721             _ => intravisit::walk_pat(self, pat),
 722         }
 723     }
 724 }