src/librustc_mir/hair/pattern/check_match.rs

   1 use super::_match::Usefulness::*;
   2 use super::_match::WitnessPreference::*;
   3 use super::_match::{expand_pattern, is_useful, MatchCheckCtxt, Matrix, PatStack};
   4
   5 use super::{PatCtxt, PatKind, PatternError};
   6
   7 use rustc::lint;
   8 use rustc::session::Session;
   9 use rustc::ty::subst::{InternalSubsts, SubstsRef};
  10 use rustc::ty::{self, Ty, TyCtxt};
  11 use rustc_errors::{Applicability, DiagnosticBuilder};
  12
  13 use rustc::hir::def::*;
  14 use rustc::hir::def_id::DefId;
  15 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  16 use rustc::hir::HirId;
  17 use rustc::hir::{self, Pat};
  18
  19 use std::slice;
  20
  21 use syntax_pos::{MultiSpan, Span};
  22
  23 crate fn check_match(tcx: TyCtxt<'_>, def_id: DefId) {
  24     let body_id = match tcx.hir().as_local_hir_id(def_id) {
  25         None => return,
  26         Some(id) => tcx.hir().body_owned_by(id),
  27     };
  28
  29     let mut visitor = MatchVisitor {
  30         tcx,
  31         tables: tcx.body_tables(body_id),
  32         param_env: tcx.param_env(def_id),
  33         identity_substs: InternalSubsts::identity_for_item(tcx, def_id),
  34     };
  35     visitor.visit_body(tcx.hir().body(body_id));
  36 }
  37
  38 fn create_e0004(sess: &Session, sp: Span, error_message: String) -> DiagnosticBuilder<'_> {
  39     struct_span_err!(sess, sp, E0004, "{}", &error_message)
  40 }
  41
  42 struct MatchVisitor<'a, 'tcx> {
  43     tcx: TyCtxt<'tcx>,
  44     tables: &'a ty::TypeckTables<'tcx>,
  45     param_env: ty::ParamEnv<'tcx>,
  46     identity_substs: SubstsRef<'tcx>,
  47 }
  48
  49 impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, 'tcx> {
  50     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  51         NestedVisitorMap::None
  52     }
  53
  54     fn visit_expr(&mut self, ex: &'tcx hir::Expr) {
  55         intravisit::walk_expr(self, ex);
  56
  57         if let hir::ExprKind::Match(ref scrut, ref arms, source) = ex.kind {
  58             self.check_match(scrut, arms, source);
  59         }
  60     }
  61
  62     fn visit_local(&mut self, loc: &'tcx hir::Local) {
  63         intravisit::walk_local(self, loc);
  64
  65         let (msg, sp) = match loc.source {
  66             hir::LocalSource::Normal => ("local binding", Some(loc.span)),
  67             hir::LocalSource::ForLoopDesugar => ("`for` loop binding", None),
  68             hir::LocalSource::AsyncFn => ("async fn binding", None),
  69             hir::LocalSource::AwaitDesugar => ("`await` future binding", None),
  70         };
  71         self.check_irrefutable(&loc.pat, msg, sp);
  72
  73         // Check legality of move bindings and `@` patterns.
  74         self.check_patterns(false, &loc.pat);
  75     }
  76
  77     fn visit_body(&mut self, body: &'tcx hir::Body) {
  78         intravisit::walk_body(self, body);
  79
  80         for param in &body.params {
  81             self.check_irrefutable(&param.pat, "function argument", None);
  82             self.check_patterns(false, &param.pat);
  83         }
  84     }
  85 }
  86
  87 impl PatCtxt<'_, '_> {
  88     fn report_inlining_errors(&self, pat_span: Span) {
  89         for error in &self.errors {
  90             match *error {
  91                 PatternError::StaticInPattern(span) => {
  92                     self.span_e0158(span, "statics cannot be referenced in patterns")
  93                 }
  94                 PatternError::AssocConstInPattern(span) => {
  95                     self.span_e0158(span, "associated consts cannot be referenced in patterns")
  96                 }
  97                 PatternError::FloatBug => {
  98                     // FIXME(#31407) this is only necessary because float parsing is buggy
  99                     ::rustc::mir::interpret::struct_error(
 100                         self.tcx.at(pat_span),
 101                         "could not evaluate float literal (see issue #31407)",
 102                     )
 103                     .emit();
 104                 }
 105                 PatternError::NonConstPath(span) => {
 106                     ::rustc::mir::interpret::struct_error(
 107                         self.tcx.at(span),
 108                         "runtime values cannot be referenced in patterns",
 109                     )
 110                     .emit();
 111                 }
 112             }
 113         }
 114     }
 115
 116     fn span_e0158(&self, span: Span, text: &str) {
 117         span_err!(self.tcx.sess, span, E0158, "{}", text)
 118     }
 119 }
 120
 121 impl<'tcx> MatchVisitor<'_, 'tcx> {
 122     fn check_patterns(&mut self, has_guard: bool, pat: &Pat) {
 123         check_legality_of_move_bindings(self, has_guard, pat);
 124         check_legality_of_bindings_in_at_patterns(self, pat);
 125     }
 126
 127     fn check_match(&mut self, scrut: &hir::Expr, arms: &'tcx [hir::Arm], source: hir::MatchSource) {
 128         for arm in arms {
 129             // First, check legality of move bindings.
 130             self.check_patterns(arm.guard.is_some(), &arm.pat);
 131
 132             // Second, perform some lints.
 133             check_for_bindings_named_same_as_variants(self, &arm.pat);
 134         }
 135
 136         let module = self.tcx.hir().get_module_parent(scrut.hir_id);
 137         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 138             let mut have_errors = false;
 139
 140             let inlined_arms: Vec<(Vec<_>, _)> = arms
 141                 .iter()
 142                 .map(|arm| {
 143                     (
 144                         // HACK(or_patterns; Centril | dlrobertson): Remove this and
 145                         // correctly handle exhaustiveness checking for nested or-patterns.
 146                         match &arm.pat.kind {
 147                             hir::PatKind::Or(pats) => pats,
 148                             _ => std::slice::from_ref(&arm.pat),
 149                         }
 150                         .iter()
 151                         .map(|pat| {
 152                             let mut patcx = PatCtxt::new(
 153                                 self.tcx,
 154                                 self.param_env.and(self.identity_substs),
 155                                 self.tables,
 156                             );
 157                             patcx.include_lint_checks();
 158                             let pattern = cx
 159                                 .pattern_arena
 160                                 .alloc(expand_pattern(cx, patcx.lower_pattern(&pat)))
 161                                 as &_;
 162                             if !patcx.errors.is_empty() {
 163                                 patcx.report_inlining_errors(pat.span);
 164                                 have_errors = true;
 165                             }
 166                             (pattern, &**pat)
 167                         })
 168                         .collect(),
 169                         arm.guard.as_ref().map(|g| match g {
 170                             hir::Guard::If(ref e) => &**e,
 171                         }),
 172                     )
 173                 })
 174                 .collect();
 175
 176             // Bail out early if inlining failed.
 177             if have_errors {
 178                 return;
 179             }
 180
 181             // Fourth, check for unreachable arms.
 182             check_arms(cx, &inlined_arms, source);
 183
 184             // Then, if the match has no arms, check whether the scrutinee
 185             // is uninhabited.
 186             let pat_ty = self.tables.node_type(scrut.hir_id);
 187             let module = self.tcx.hir().get_module_parent(scrut.hir_id);
 188             let mut def_span = None;
 189             let mut missing_variants = vec![];
 190             if inlined_arms.is_empty() {
 191                 let scrutinee_is_uninhabited = if self.tcx.features().exhaustive_patterns {
 192                     self.tcx.is_ty_uninhabited_from(module, pat_ty)
 193                 } else {
 194                     match pat_ty.kind {
 195                         ty::Never => true,
 196                         ty::Adt(def, _) => {
 197                             def_span = self.tcx.hir().span_if_local(def.did);
 198                             if def.variants.len() < 4 && !def.variants.is_empty() {
 199                                 // keep around to point at the definition of non-covered variants
 200                                 missing_variants =
 201                                     def.variants.iter().map(|variant| variant.ident).collect();
 202                             }
 203
 204                             let is_non_exhaustive_and_non_local =
 205                                 def.is_variant_list_non_exhaustive() && !def.did.is_local();
 206
 207                             !(is_non_exhaustive_and_non_local) && def.variants.is_empty()
 208                         }
 209                         _ => false,
 210                     }
 211                 };
 212                 if !scrutinee_is_uninhabited {
 213                     // We know the type is inhabited, so this must be wrong
 214                     let mut err = create_e0004(
 215                         self.tcx.sess,
 216                         scrut.span,
 217                         format!(
 218                             "non-exhaustive patterns: {}",
 219                             match missing_variants.len() {
 220                                 0 => format!("type `{}` is non-empty", pat_ty),
 221                                 1 => format!(
 222                                     "pattern `{}` of type `{}` is not handled",
 223                                     missing_variants[0].name, pat_ty,
 224                                 ),
 225                                 _ => format!(
 226                                     "multiple patterns of type `{}` are not handled",
 227                                     pat_ty
 228                                 ),
 229                             }
 230                         ),
 231                     );
 232                     err.help(
 233                         "ensure that all possible cases are being handled, \
 234                          possibly by adding wildcards or more match arms",
 235                     );
 236                     if let Some(sp) = def_span {
 237                         err.span_label(sp, format!("`{}` defined here", pat_ty));
 238                     }
 239                     // point at the definition of non-covered enum variants
 240                     for variant in &missing_variants {
 241                         err.span_label(variant.span, "variant not covered");
 242                     }
 243                     err.emit();
 244                 }
 245                 // If the type *is* uninhabited, it's vacuously exhaustive
 246                 return;
 247             }
 248
 249             let matrix: Matrix<'_, '_> = inlined_arms
 250                 .iter()
 251                 .filter(|&&(_, guard)| guard.is_none())
 252                 .flat_map(|arm| &arm.0)
 253                 .map(|pat| PatStack::from_pattern(pat.0))
 254                 .collect();
 255             let scrut_ty = self.tables.node_type(scrut.hir_id);
 256             check_exhaustive(cx, scrut_ty, scrut.span, &matrix, scrut.hir_id);
 257         })
 258     }
 259
 260     fn check_irrefutable(&self, pat: &'tcx Pat, origin: &str, sp: Option<Span>) {
 261         let module = self.tcx.hir().get_module_parent(pat.hir_id);
 262         MatchCheckCtxt::create_and_enter(self.tcx, self.param_env, module, |ref mut cx| {
 263             let mut patcx =
 264                 PatCtxt::new(self.tcx, self.param_env.and(self.identity_substs), self.tables);
 265             patcx.include_lint_checks();
 266             let pattern = patcx.lower_pattern(pat);
 267             let pattern_ty = pattern.ty;
 268             let pattern = expand_pattern(cx, pattern);
 269             let pats: Matrix<'_, '_> = vec![PatStack::from_pattern(&pattern)].into_iter().collect();
 270
 271             let witnesses = match check_not_useful(cx, pattern_ty, &pats, pat.hir_id) {
 272                 Ok(_) => return,
 273                 Err(err) => err,
 274             };
 275
 276             let joined_patterns = joined_uncovered_patterns(&witnesses);
 277             let mut err = struct_span_err!(
 278                 self.tcx.sess,
 279                 pat.span,
 280                 E0005,
 281                 "refutable pattern in {}: {} not covered",
 282                 origin,
 283                 joined_patterns
 284             );
 285             let suggest_if_let = match &pat.kind {
 286                 hir::PatKind::Path(hir::QPath::Resolved(None, path))
 287                     if path.segments.len() == 1 && path.segments[0].args.is_none() =>
 288                 {
 289                     const_not_var(&mut err, cx.tcx, pat, path);
 290                     false
 291                 }
 292                 _ => {
 293                     err.span_label(
 294                         pat.span,
 295                         pattern_not_covered_label(&witnesses, &joined_patterns),
 296                     );
 297                     true
 298                 }
 299             };
 300
 301             if let (Some(span), true) = (sp, suggest_if_let) {
 302                 err.note(
 303                     "`let` bindings require an \"irrefutable pattern\", like a `struct` or \
 304                      an `enum` with only one variant",
 305                 );
 306                 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
 307                     err.span_suggestion(
 308                         span,
 309                         "you might want to use `if let` to ignore the variant that isn't matched",
 310                         format!("if {} {{ /* */ }}", &snippet[..snippet.len() - 1]),
 311                         Applicability::HasPlaceholders,
 312                     );
 313                 }
 314                 err.note(
 315                     "for more information, visit \
 316                      https://doc.rust-lang.org/book/ch18-02-refutability.html",
 317                 );
 318             }
 319
 320             adt_defined_here(cx, &mut err, pattern_ty, &witnesses);
 321             err.emit();
 322         });
 323     }
 324 }
 325
 326 /// A path pattern was interpreted as a constant, not a new variable.
 327 /// This caused an irrefutable match failure in e.g. `let`.
 328 fn const_not_var(err: &mut DiagnosticBuilder<'_>, tcx: TyCtxt<'_>, pat: &Pat, path: &hir::Path) {
 329     let descr = path.res.descr();
 330     err.span_label(
 331         pat.span,
 332         format!("interpreted as {} {} pattern, not a new variable", path.res.article(), descr,),
 333     );
 334
 335     err.span_suggestion(
 336         pat.span,
 337         "introduce a variable instead",
 338         format!("{}_var", path.segments[0].ident).to_lowercase(),
 339         // Cannot use `MachineApplicable` as it's not really *always* correct
 340         // because there may be such an identifier in scope or the user maybe
 341         // really wanted to match against the constant. This is quite unlikely however.
 342         Applicability::MaybeIncorrect,
 343     );
 344
 345     if let Some(span) = tcx.hir().res_span(path.res) {
 346         err.span_label(span, format!("{} defined here", descr));
 347     }
 348 }
 349
 350 fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_>, pat: &Pat) {
 351     pat.walk(|p| {
 352         if let hir::PatKind::Binding(_, _, ident, None) = p.kind {
 353             if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 354                 if bm != ty::BindByValue(hir::Mutability::Immutable) {
 355                     // Nothing to check.
 356                     return true;
 357                 }
 358                 let pat_ty = cx.tables.pat_ty(p);
 359                 if let ty::Adt(edef, _) = pat_ty.kind {
 360                     if edef.is_enum()
 361                         && edef.variants.iter().any(|variant| {
 362                             variant.ident == ident && variant.ctor_kind == CtorKind::Const
 363                         })
 364                     {
 365                         let ty_path = cx.tcx.def_path_str(edef.did);
 366                         let mut err = struct_span_warn!(
 367                             cx.tcx.sess,
 368                             p.span,
 369                             E0170,
 370                             "pattern binding `{}` is named the same as one \
 371                              of the variants of the type `{}`",
 372                             ident,
 373                             ty_path
 374                         );
 375                         err.span_suggestion(
 376                             p.span,
 377                             "to match on the variant, qualify the path",
 378                             format!("{}::{}", ty_path, ident),
 379                             Applicability::MachineApplicable,
 380                         );
 381                         err.emit();
 382                     }
 383                 }
 384             } else {
 385                 cx.tcx.sess.delay_span_bug(p.span, "missing binding mode");
 386             }
 387         }
 388         true
 389     });
 390 }
 391
 392 /// Checks for common cases of "catchall" patterns that may not be intended as such.
 393 fn pat_is_catchall(pat: &Pat) -> bool {
 394     match pat.kind {
 395         hir::PatKind::Binding(.., None) => true,
 396         hir::PatKind::Binding(.., Some(ref s)) => pat_is_catchall(s),
 397         hir::PatKind::Ref(ref s, _) => pat_is_catchall(s),
 398         hir::PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(&p)),
 399         _ => false,
 400     }
 401 }
 402
 403 // Check for unreachable patterns
 404 fn check_arms<'tcx>(
 405     cx: &mut MatchCheckCtxt<'_, 'tcx>,
 406     arms: &[(Vec<(&super::Pat<'tcx>, &hir::Pat)>, Option<&hir::Expr>)],
 407     source: hir::MatchSource,
 408 ) {
 409     let mut seen = Matrix::empty();
 410     let mut catchall = None;
 411     for (arm_index, &(ref pats, guard)) in arms.iter().enumerate() {
 412         for &(pat, hir_pat) in pats {
 413             let v = PatStack::from_pattern(pat);
 414
 415             match is_useful(cx, &seen, &v, LeaveOutWitness, hir_pat.hir_id) {
 416                 NotUseful => {
 417                     match source {
 418                         hir::MatchSource::IfDesugar { .. } | hir::MatchSource::WhileDesugar => {
 419                             bug!()
 420                         }
 421                         hir::MatchSource::IfLetDesugar { .. } => {
 422                             cx.tcx.lint_hir(
 423                                 lint::builtin::IRREFUTABLE_LET_PATTERNS,
 424                                 hir_pat.hir_id,
 425                                 pat.span,
 426                                 "irrefutable if-let pattern",
 427                             );
 428                         }
 429
 430                         hir::MatchSource::WhileLetDesugar => {
 431                             // check which arm we're on.
 432                             match arm_index {
 433                                 // The arm with the user-specified pattern.
 434                                 0 => {
 435                                     cx.tcx.lint_hir(
 436                                         lint::builtin::UNREACHABLE_PATTERNS,
 437                                         hir_pat.hir_id,
 438                                         pat.span,
 439                                         "unreachable pattern",
 440                                     );
 441                                 }
 442                                 // The arm with the wildcard pattern.
 443                                 1 => {
 444                                     cx.tcx.lint_hir(
 445                                         lint::builtin::IRREFUTABLE_LET_PATTERNS,
 446                                         hir_pat.hir_id,
 447                                         pat.span,
 448                                         "irrefutable while-let pattern",
 449                                     );
 450                                 }
 451                                 _ => bug!(),
 452                             }
 453                         }
 454
 455                         hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => {
 456                             let mut err = cx.tcx.struct_span_lint_hir(
 457                                 lint::builtin::UNREACHABLE_PATTERNS,
 458                                 hir_pat.hir_id,
 459                                 pat.span,
 460                                 "unreachable pattern",
 461                             );
 462                             // if we had a catchall pattern, hint at that
 463                             if let Some(catchall) = catchall {
 464                                 err.span_label(pat.span, "unreachable pattern");
 465                                 err.span_label(catchall, "matches any value");
 466                             }
 467                             err.emit();
 468                         }
 469
 470                         // Unreachable patterns in try and await expressions occur when one of
 471                         // the arms are an uninhabited type. Which is OK.
 472                         hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}
 473                     }
 474                 }
 475                 Useful => (),
 476                 UsefulWithWitness(_) => bug!(),
 477             }
 478             if guard.is_none() {
 479                 seen.push(v);
 480                 if catchall.is_none() && pat_is_catchall(hir_pat) {
 481                     catchall = Some(pat.span);
 482                 }
 483             }
 484         }
 485     }
 486 }
 487
 488 fn check_not_useful(
 489     cx: &mut MatchCheckCtxt<'_, 'tcx>,
 490     ty: Ty<'tcx>,
 491     matrix: &Matrix<'_, 'tcx>,
 492     hir_id: HirId,
 493 ) -> Result<(), Vec<super::Pat<'tcx>>> {
 494     let wild_pattern = super::Pat::wildcard_from_ty(ty);
 495     match is_useful(cx, matrix, &PatStack::from_pattern(&wild_pattern), ConstructWitness, hir_id) {
 496         NotUseful => Ok(()), // This is good, wildcard pattern isn't reachable.
 497         UsefulWithWitness(pats) => Err(if pats.is_empty() {
 498             vec![wild_pattern]
 499         } else {
 500             pats.into_iter().map(|w| w.single_pattern()).collect()
 501         }),
 502         Useful => bug!(),
 503     }
 504 }
 505
 506 fn check_exhaustive<'tcx>(
 507     cx: &mut MatchCheckCtxt<'_, 'tcx>,
 508     scrut_ty: Ty<'tcx>,
 509     sp: Span,
 510     matrix: &Matrix<'_, 'tcx>,
 511     hir_id: HirId,
 512 ) {
 513     let witnesses = match check_not_useful(cx, scrut_ty, matrix, hir_id) {
 514         Ok(_) => return,
 515         Err(err) => err,
 516     };
 517
 518     let joined_patterns = joined_uncovered_patterns(&witnesses);
 519     let mut err = create_e0004(
 520         cx.tcx.sess,
 521         sp,
 522         format!("non-exhaustive patterns: {} not covered", joined_patterns),
 523     );
 524     err.span_label(sp, pattern_not_covered_label(&witnesses, &joined_patterns));
 525     adt_defined_here(cx, &mut err, scrut_ty, &witnesses);
 526     err.help(
 527         "ensure that all possible cases are being handled, \
 528          possibly by adding wildcards or more match arms",
 529     )
 530     .emit();
 531 }
 532
 533 fn joined_uncovered_patterns(witnesses: &[super::Pat<'_>]) -> String {
 534     const LIMIT: usize = 3;
 535     match witnesses {
 536         [] => bug!(),
 537         [witness] => format!("`{}`", witness),
 538         [head @ .., tail] if head.len() < LIMIT => {
 539             let head: Vec<_> = head.iter().map(<_>::to_string).collect();
 540             format!("`{}` and `{}`", head.join("`, `"), tail)
 541         }
 542         _ => {
 543             let (head, tail) = witnesses.split_at(LIMIT);
 544             let head: Vec<_> = head.iter().map(<_>::to_string).collect();
 545             format!("`{}` and {} more", head.join("`, `"), tail.len())
 546         }
 547     }
 548 }
 549
 550 fn pattern_not_covered_label(witnesses: &[super::Pat<'_>], joined_patterns: &str) -> String {
 551     format!("pattern{} {} not covered", rustc_errors::pluralize!(witnesses.len()), joined_patterns)
 552 }
 553
 554 /// Point at the definition of non-covered `enum` variants.
 555 fn adt_defined_here(
 556     cx: &MatchCheckCtxt<'_, '_>,
 557     err: &mut DiagnosticBuilder<'_>,
 558     ty: Ty<'_>,
 559     witnesses: &[super::Pat<'_>],
 560 ) {
 561     let ty = ty.peel_refs();
 562     if let ty::Adt(def, _) = ty.kind {
 563         if let Some(sp) = cx.tcx.hir().span_if_local(def.did) {
 564             err.span_label(sp, format!("`{}` defined here", ty));
 565         }
 566
 567         if witnesses.len() < 4 {
 568             for sp in maybe_point_at_variant(ty, &witnesses) {
 569                 err.span_label(sp, "not covered");
 570             }
 571         }
 572     }
 573 }
 574
 575 fn maybe_point_at_variant(ty: Ty<'_>, patterns: &[super::Pat<'_>]) -> Vec<Span> {
 576     let mut covered = vec![];
 577     if let ty::Adt(def, _) = ty.kind {
 578         // Don't point at variants that have already been covered due to other patterns to avoid
 579         // visual clutter.
 580         for pattern in patterns {
 581             use PatKind::{AscribeUserType, Deref, Leaf, Or, Variant};
 582             match &*pattern.kind {
 583                 AscribeUserType { subpattern, .. } | Deref { subpattern } => {
 584                     covered.extend(maybe_point_at_variant(ty, slice::from_ref(&subpattern)));
 585                 }
 586                 Variant { adt_def, variant_index, subpatterns, .. } if adt_def.did == def.did => {
 587                     let sp = def.variants[*variant_index].ident.span;
 588                     if covered.contains(&sp) {
 589                         continue;
 590                     }
 591                     covered.push(sp);
 592
 593                     let pats = subpatterns
 594                         .iter()
 595                         .map(|field_pattern| field_pattern.pattern.clone())
 596                         .collect::<Box<[_]>>();
 597                     covered.extend(maybe_point_at_variant(ty, &pats));
 598                 }
 599                 Leaf { subpatterns } => {
 600                     let pats = subpatterns
 601                         .iter()
 602                         .map(|field_pattern| field_pattern.pattern.clone())
 603                         .collect::<Box<[_]>>();
 604                     covered.extend(maybe_point_at_variant(ty, &pats));
 605                 }
 606                 Or { pats } => {
 607                     let pats = pats.iter().cloned().collect::<Box<[_]>>();
 608                     covered.extend(maybe_point_at_variant(ty, &pats));
 609                 }
 610                 _ => {}
 611             }
 612         }
 613     }
 614     covered
 615 }
 616
 617 // Check the legality of legality of by-move bindings.
 618 fn check_legality_of_move_bindings(cx: &mut MatchVisitor<'_, '_>, has_guard: bool, pat: &Pat) {
 619     let mut by_ref_span = None;
 620     pat.each_binding(|_, hir_id, span, _| {
 621         if let Some(&bm) = cx.tables.pat_binding_modes().get(hir_id) {
 622             if let ty::BindByReference(..) = bm {
 623                 by_ref_span = Some(span);
 624             }
 625         } else {
 626             cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 627         }
 628     });
 629
 630     let span_vec = &mut Vec::new();
 631     let mut check_move = |p: &Pat, sub: Option<&Pat>| {
 632         // Check legality of moving out of the enum.
 633         //
 634         // `x @ Foo(..)` is legal, but `x @ Foo(y)` isn't.
 635         if sub.map_or(false, |p| p.contains_bindings()) {
 636             struct_span_err!(cx.tcx.sess, p.span, E0007, "cannot bind by-move with sub-bindings")
 637                 .span_label(p.span, "binds an already bound by-move value by moving it")
 638                 .emit();
 639         } else if !has_guard && by_ref_span.is_some() {
 640             span_vec.push(p.span);
 641         }
 642     };
 643
 644     pat.walk(|p| {
 645         if let hir::PatKind::Binding(.., sub) = &p.kind {
 646             if let Some(&bm) = cx.tables.pat_binding_modes().get(p.hir_id) {
 647                 if let ty::BindByValue(..) = bm {
 648                     let pat_ty = cx.tables.node_type(p.hir_id);
 649                     if !pat_ty.is_copy_modulo_regions(cx.tcx, cx.param_env, pat.span) {
 650                         check_move(p, sub.as_deref());
 651                     }
 652                 }
 653             } else {
 654                 cx.tcx.sess.delay_span_bug(pat.span, "missing binding mode");
 655             }
 656         }
 657         true
 658     });
 659
 660     if !span_vec.is_empty() {
 661         let mut err = struct_span_err!(
 662             cx.tcx.sess,
 663             MultiSpan::from_spans(span_vec.clone()),
 664             E0009,
 665             "cannot bind by-move and by-ref in the same pattern",
 666         );
 667         if let Some(by_ref_span) = by_ref_span {
 668             err.span_label(by_ref_span, "both by-ref and by-move used");
 669         }
 670         for span in span_vec.iter() {
 671             err.span_label(*span, "by-move pattern here");
 672         }
 673         err.emit();
 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, bindings_allowed: true }.visit_pat(pat);
 682 }
 683
 684 struct AtBindingPatternVisitor<'a, 'b, 'tcx> {
 685     cx: &'a MatchVisitor<'b, 'tcx>,
 686     bindings_allowed: bool,
 687 }
 688
 689 impl<'v> Visitor<'v> for AtBindingPatternVisitor<'_, '_, '_> {
 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.kind {
 696             hir::PatKind::Binding(.., ref subpat) => {
 697                 if !self.bindings_allowed {
 698                     struct_span_err!(
 699                         self.cx.tcx.sess,
 700                         pat.span,
 701                         E0303,
 702                         "pattern bindings are not allowed after an `@`"
 703                     )
 704                     .span_label(pat.span, "not allowed after `@`")
 705                     .emit();
 706                 }
 707
 708                 if subpat.is_some() {
 709                     let bindings_were_allowed = self.bindings_allowed;
 710                     self.bindings_allowed = false;
 711                     intravisit::walk_pat(self, pat);
 712                     self.bindings_allowed = bindings_were_allowed;
 713                 }
 714             }
 715             _ => intravisit::walk_pat(self, pat),
 716         }
 717     }
 718 }