src/librustc_mir/hair/pattern/mod.rs

   1 //! Validation of patterns/matches.
   2
   3 mod _match;
   4 mod check_match;
   5 mod const_to_pat;
   6
   7 pub(crate) use self::check_match::check_match;
   8
   9 use crate::hair::util::UserAnnotatedTyHelpers;
  10 use crate::hair::constant::*;
  11
  12 use rustc::mir::{Field, BorrowKind, Mutability};
  13 use rustc::mir::{UserTypeProjection};
  14 use rustc::mir::interpret::{GlobalId, ConstValue, get_slice_bytes, sign_extend};
  15 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, UserType, DefIdTree};
  16 use rustc::ty::{CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations};
  17 use rustc::ty::subst::{SubstsRef, GenericArg};
  18 use rustc::ty::layout::VariantIdx;
  19 use rustc::hir::{self, RangeEnd};
  20 use rustc::hir::def::{CtorOf, Res, DefKind, CtorKind};
  21 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  22 use rustc::hir::ptr::P;
  23
  24 use rustc_index::vec::Idx;
  25
  26 use std::cmp::Ordering;
  27 use std::fmt;
  28 use syntax::ast;
  29 use syntax_pos::Span;
  30
  31 #[derive(Clone, Debug)]
  32 pub enum PatternError {
  33     AssocConstInPattern(Span),
  34     StaticInPattern(Span),
  35     FloatBug,
  36     NonConstPath(Span),
  37 }
  38
  39 #[derive(Copy, Clone, Debug)]
  40 pub enum BindingMode {
  41     ByValue,
  42     ByRef(BorrowKind),
  43 }
  44
  45 #[derive(Clone, Debug)]
  46 pub struct FieldPat<'tcx> {
  47     pub field: Field,
  48     pub pattern: Pat<'tcx>,
  49 }
  50
  51 #[derive(Clone, Debug)]
  52 pub struct Pat<'tcx> {
  53     pub ty: Ty<'tcx>,
  54     pub span: Span,
  55     pub kind: Box<PatKind<'tcx>>,
  56 }
  57
  58
  59 #[derive(Copy, Clone, Debug, PartialEq)]
  60 pub struct PatTyProj<'tcx> {
  61     pub user_ty: CanonicalUserType<'tcx>,
  62 }
  63
  64 impl<'tcx> PatTyProj<'tcx> {
  65     pub(crate) fn from_user_type(user_annotation: CanonicalUserType<'tcx>) -> Self {
  66         Self {
  67             user_ty: user_annotation,
  68         }
  69     }
  70
  71     pub(crate) fn user_ty(
  72         self,
  73         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
  74         inferred_ty: Ty<'tcx>,
  75         span: Span,
  76     ) -> UserTypeProjection {
  77         UserTypeProjection {
  78             base: annotations.push(CanonicalUserTypeAnnotation {
  79                 span,
  80                 user_ty: self.user_ty,
  81                 inferred_ty,
  82             }),
  83             projs: Vec::new(),
  84         }
  85     }
  86 }
  87
  88 #[derive(Copy, Clone, Debug, PartialEq)]
  89 pub struct Ascription<'tcx> {
  90     pub user_ty: PatTyProj<'tcx>,
  91     /// Variance to use when relating the type `user_ty` to the **type of the value being
  92     /// matched**. Typically, this is `Variance::Covariant`, since the value being matched must
  93     /// have a type that is some subtype of the ascribed type.
  94     ///
  95     /// Note that this variance does not apply for any bindings within subpatterns. The type
  96     /// assigned to those bindings must be exactly equal to the `user_ty` given here.
  97     ///
  98     /// The only place where this field is not `Covariant` is when matching constants, where
  99     /// we currently use `Contravariant` -- this is because the constant type just needs to
 100     /// be "comparable" to the type of the input value. So, for example:
 101     ///
 102     /// ```text
 103     /// match x { "foo" => .. }
 104     /// ```
 105     ///
 106     /// requires that `&'static str <: T_x`, where `T_x` is the type of `x`. Really, we should
 107     /// probably be checking for a `PartialEq` impl instead, but this preserves the behavior
 108     /// of the old type-check for now. See #57280 for details.
 109     pub variance: ty::Variance,
 110     pub user_ty_span: Span,
 111 }
 112
 113 #[derive(Clone, Debug)]
 114 pub enum PatKind<'tcx> {
 115     Wild,
 116
 117     AscribeUserType {
 118         ascription: Ascription<'tcx>,
 119         subpattern: Pat<'tcx>,
 120     },
 121
 122     /// `x`, `ref x`, `x @ P`, etc.
 123     Binding {
 124         mutability: Mutability,
 125         name: ast::Name,
 126         mode: BindingMode,
 127         var: hir::HirId,
 128         ty: Ty<'tcx>,
 129         subpattern: Option<Pat<'tcx>>,
 130     },
 131
 132     /// `Foo(...)` or `Foo{...}` or `Foo`, where `Foo` is a variant name from an ADT with
 133     /// multiple variants.
 134     Variant {
 135         adt_def: &'tcx AdtDef,
 136         substs: SubstsRef<'tcx>,
 137         variant_index: VariantIdx,
 138         subpatterns: Vec<FieldPat<'tcx>>,
 139     },
 140
 141     /// `(...)`, `Foo(...)`, `Foo{...}`, or `Foo`, where `Foo` is a variant name from an ADT with
 142     /// a single variant.
 143     Leaf {
 144         subpatterns: Vec<FieldPat<'tcx>>,
 145     },
 146
 147     /// `box P`, `&P`, `&mut P`, etc.
 148     Deref {
 149         subpattern: Pat<'tcx>,
 150     },
 151
 152     Constant {
 153         value: &'tcx ty::Const<'tcx>,
 154     },
 155
 156     Range(PatRange<'tcx>),
 157
 158     /// Matches against a slice, checking the length and extracting elements.
 159     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 160     /// e.g., `&[ref xs @ ..]`.
 161     Slice {
 162         prefix: Vec<Pat<'tcx>>,
 163         slice: Option<Pat<'tcx>>,
 164         suffix: Vec<Pat<'tcx>>,
 165     },
 166
 167     /// Fixed match against an array; irrefutable.
 168     Array {
 169         prefix: Vec<Pat<'tcx>>,
 170         slice: Option<Pat<'tcx>>,
 171         suffix: Vec<Pat<'tcx>>,
 172     },
 173
 174     /// An or-pattern, e.g. `p | q`.
 175     /// Invariant: `pats.len() >= 2`.
 176     Or {
 177         pats: Vec<Pat<'tcx>>,
 178     },
 179 }
 180
 181 #[derive(Copy, Clone, Debug, PartialEq)]
 182 pub struct PatRange<'tcx> {
 183     pub lo: &'tcx ty::Const<'tcx>,
 184     pub hi: &'tcx ty::Const<'tcx>,
 185     pub end: RangeEnd,
 186 }
 187
 188 impl<'tcx> fmt::Display for Pat<'tcx> {
 189     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 190         // Printing lists is a chore.
 191         let mut first = true;
 192         let mut start_or_continue = |s| {
 193             if first {
 194                 first = false;
 195                 ""
 196             } else {
 197                 s
 198             }
 199         };
 200         let mut start_or_comma = || start_or_continue(", ");
 201
 202         match *self.kind {
 203             PatKind::Wild => write!(f, "_"),
 204             PatKind::AscribeUserType { ref subpattern, .. } =>
 205                 write!(f, "{}: _", subpattern),
 206             PatKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 207                 let is_mut = match mode {
 208                     BindingMode::ByValue => mutability == Mutability::Mut,
 209                     BindingMode::ByRef(bk) => {
 210                         write!(f, "ref ")?;
 211                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 212                     }
 213                 };
 214                 if is_mut {
 215                     write!(f, "mut ")?;
 216                 }
 217                 write!(f, "{}", name)?;
 218                 if let Some(ref subpattern) = *subpattern {
 219                     write!(f, " @ {}", subpattern)?;
 220                 }
 221                 Ok(())
 222             }
 223             PatKind::Variant { ref subpatterns, .. } |
 224             PatKind::Leaf { ref subpatterns } => {
 225                 let variant = match *self.kind {
 226                     PatKind::Variant { adt_def, variant_index, .. } => {
 227                         Some(&adt_def.variants[variant_index])
 228                     }
 229                     _ => if let ty::Adt(adt, _) = self.ty.kind {
 230                         if !adt.is_enum() {
 231                             Some(&adt.variants[VariantIdx::new(0)])
 232                         } else {
 233                             None
 234                         }
 235                     } else {
 236                         None
 237                     }
 238                 };
 239
 240                 if let Some(variant) = variant {
 241                     write!(f, "{}", variant.ident)?;
 242
 243                     // Only for Adt we can have `S {...}`,
 244                     // which we handle separately here.
 245                     if variant.ctor_kind == CtorKind::Fictive {
 246                         write!(f, " {{ ")?;
 247
 248                         let mut printed = 0;
 249                         for p in subpatterns {
 250                             if let PatKind::Wild = *p.pattern.kind {
 251                                 continue;
 252                             }
 253                             let name = variant.fields[p.field.index()].ident;
 254                             write!(f, "{}{}: {}", start_or_comma(), name, p.pattern)?;
 255                             printed += 1;
 256                         }
 257
 258                         if printed < variant.fields.len() {
 259                             write!(f, "{}..", start_or_comma())?;
 260                         }
 261
 262                         return write!(f, " }}");
 263                     }
 264                 }
 265
 266                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 267                 if num_fields != 0 || variant.is_none() {
 268                     write!(f, "(")?;
 269                     for i in 0..num_fields {
 270                         write!(f, "{}", start_or_comma())?;
 271
 272                         // Common case: the field is where we expect it.
 273                         if let Some(p) = subpatterns.get(i) {
 274                             if p.field.index() == i {
 275                                 write!(f, "{}", p.pattern)?;
 276                                 continue;
 277                             }
 278                         }
 279
 280                         // Otherwise, we have to go looking for it.
 281                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 282                             write!(f, "{}", p.pattern)?;
 283                         } else {
 284                             write!(f, "_")?;
 285                         }
 286                     }
 287                     write!(f, ")")?;
 288                 }
 289
 290                 Ok(())
 291             }
 292             PatKind::Deref { ref subpattern } => {
 293                 match self.ty.kind {
 294                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 295                     ty::Ref(_, _, mutbl) => {
 296                         write!(f, "&{}", mutbl.prefix_str())?;
 297                     }
 298                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 299                 }
 300                 write!(f, "{}", subpattern)
 301             }
 302             PatKind::Constant { value } => {
 303                 write!(f, "{}", value)
 304             }
 305             PatKind::Range(PatRange { lo, hi, end }) => {
 306                 write!(f, "{}", lo)?;
 307                 write!(f, "{}", end)?;
 308                 write!(f, "{}", hi)
 309             }
 310             PatKind::Slice { ref prefix, ref slice, ref suffix } |
 311             PatKind::Array { ref prefix, ref slice, ref suffix } => {
 312                 write!(f, "[")?;
 313                 for p in prefix {
 314                     write!(f, "{}{}", start_or_comma(), p)?;
 315                 }
 316                 if let Some(ref slice) = *slice {
 317                     write!(f, "{}", start_or_comma())?;
 318                     match *slice.kind {
 319                         PatKind::Wild => {}
 320                         _ => write!(f, "{}", slice)?
 321                     }
 322                     write!(f, "..")?;
 323                 }
 324                 for p in suffix {
 325                     write!(f, "{}{}", start_or_comma(), p)?;
 326                 }
 327                 write!(f, "]")
 328             }
 329             PatKind::Or { ref pats } => {
 330                 for pat in pats {
 331                     write!(f, "{}{}", start_or_continue(" | "), pat)?;
 332                 }
 333                 Ok(())
 334             }
 335         }
 336     }
 337 }
 338
 339 pub struct PatCtxt<'a, 'tcx> {
 340     pub tcx: TyCtxt<'tcx>,
 341     pub param_env: ty::ParamEnv<'tcx>,
 342     pub tables: &'a ty::TypeckTables<'tcx>,
 343     pub substs: SubstsRef<'tcx>,
 344     pub errors: Vec<PatternError>,
 345     include_lint_checks: bool,
 346 }
 347
 348 impl<'a, 'tcx> Pat<'tcx> {
 349     pub fn from_hir(
 350         tcx: TyCtxt<'tcx>,
 351         param_env_and_substs: ty::ParamEnvAnd<'tcx, SubstsRef<'tcx>>,
 352         tables: &'a ty::TypeckTables<'tcx>,
 353         pat: &'tcx hir::Pat,
 354     ) -> Self {
 355         let mut pcx = PatCtxt::new(tcx, param_env_and_substs, tables);
 356         let result = pcx.lower_pattern(pat);
 357         if !pcx.errors.is_empty() {
 358             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 359             tcx.sess.delay_span_bug(pat.span, &msg);
 360         }
 361         debug!("Pat::from_hir({:?}) = {:?}", pat, result);
 362         result
 363     }
 364 }
 365
 366 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 367     pub fn new(
 368         tcx: TyCtxt<'tcx>,
 369         param_env_and_substs: ty::ParamEnvAnd<'tcx, SubstsRef<'tcx>>,
 370         tables: &'a ty::TypeckTables<'tcx>,
 371     ) -> Self {
 372         PatCtxt {
 373             tcx,
 374             param_env: param_env_and_substs.param_env,
 375             tables,
 376             substs: param_env_and_substs.value,
 377             errors: vec![],
 378             include_lint_checks: false,
 379         }
 380     }
 381
 382     pub fn include_lint_checks(&mut self) -> &mut Self {
 383         self.include_lint_checks = true;
 384         self
 385     }
 386
 387     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pat<'tcx> {
 388         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 389         // pattern has the type that results *after* dereferencing. For example, in this code:
 390         //
 391         // ```
 392         // match &&Some(0i32) {
 393         //     Some(n) => { ... },
 394         //     _ => { ... },
 395         // }
 396         // ```
 397         //
 398         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 399         // determined in rustc_typeck::check::match). The adjustments would be
 400         //
 401         // `vec![&&Option<i32>, &Option<i32>]`.
 402         //
 403         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 404         // we wrap the unadjusted pattern in `PatKind::Deref` repeatedly, consuming the
 405         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 406         // gets the least-dereferenced type).
 407         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 408         self.tables
 409             .pat_adjustments()
 410             .get(pat.hir_id)
 411             .unwrap_or(&vec![])
 412             .iter()
 413             .rev()
 414             .fold(unadjusted_pat, |pat, ref_ty| {
 415                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 416                     Pat {
 417                         span: pat.span,
 418                         ty: ref_ty,
 419                         kind: Box::new(PatKind::Deref { subpattern: pat }),
 420                     }
 421                 },
 422             )
 423     }
 424
 425     fn lower_range_expr(
 426         &mut self,
 427         expr: &'tcx hir::Expr,
 428     ) -> (PatKind<'tcx>, Option<Ascription<'tcx>>) {
 429         match self.lower_lit(expr) {
 430             PatKind::AscribeUserType {
 431                 ascription: lo_ascription,
 432                 subpattern: Pat { kind: box kind, .. },
 433             } => (kind, Some(lo_ascription)),
 434             kind => (kind, None),
 435         }
 436     }
 437
 438     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pat<'tcx> {
 439         let mut ty = self.tables.node_type(pat.hir_id);
 440
 441         let kind = match pat.kind {
 442             hir::PatKind::Wild => PatKind::Wild,
 443
 444             hir::PatKind::Lit(ref value) => self.lower_lit(value),
 445
 446             hir::PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 447                 let (lo, lo_ascription) = self.lower_range_expr(lo_expr);
 448                 let (hi, hi_ascription) = self.lower_range_expr(hi_expr);
 449
 450                 let mut kind = match (lo, hi) {
 451                     (PatKind::Constant { value: lo }, PatKind::Constant { value: hi }) => {
 452                         assert_eq!(lo.ty, ty);
 453                         assert_eq!(hi.ty, ty);
 454                         let cmp = compare_const_vals(
 455                             self.tcx,
 456                             lo,
 457                             hi,
 458                             self.param_env,
 459                             ty,
 460                         );
 461                         match (end, cmp) {
 462                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 463                                 PatKind::Range(PatRange { lo, hi, end }),
 464                             (RangeEnd::Excluded, _) => {
 465                                 span_err!(
 466                                     self.tcx.sess,
 467                                     lo_expr.span,
 468                                     E0579,
 469                                     "lower range bound must be less than upper",
 470                                 );
 471                                 PatKind::Wild
 472                             }
 473                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 474                                 PatKind::Constant { value: lo }
 475                             }
 476                             (RangeEnd::Included, Some(Ordering::Less)) => {
 477                                 PatKind::Range(PatRange { lo, hi, end })
 478                             }
 479                             (RangeEnd::Included, _) => {
 480                                 let mut err = struct_span_err!(
 481                                     self.tcx.sess,
 482                                     lo_expr.span,
 483                                     E0030,
 484                                     "lower range bound must be less than or equal to upper"
 485                                 );
 486                                 err.span_label(
 487                                     lo_expr.span,
 488                                     "lower bound larger than upper bound",
 489                                 );
 490                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 491                                     err.note("When matching against a range, the compiler \
 492                                               verifies that the range is non-empty. Range \
 493                                               patterns include both end-points, so this is \
 494                                               equivalent to requiring the start of the range \
 495                                               to be less than or equal to the end of the range.");
 496                                 }
 497                                 err.emit();
 498                                 PatKind::Wild
 499                             }
 500                         }
 501                     },
 502                     ref pats => {
 503                         self.tcx.sess.delay_span_bug(
 504                             pat.span,
 505                             &format!(
 506                                 "found bad range pattern `{:?}` outside of error recovery",
 507                                 pats,
 508                             ),
 509                         );
 510
 511                         PatKind::Wild
 512                     },
 513                 };
 514
 515                 // If we are handling a range with associated constants (e.g.
 516                 // `Foo::<'a>::A..=Foo::B`), we need to put the ascriptions for the associated
 517                 // constants somewhere. Have them on the range pattern.
 518                 for ascription in &[lo_ascription, hi_ascription] {
 519                     if let Some(ascription) = ascription {
 520                         kind = PatKind::AscribeUserType {
 521                             ascription: *ascription,
 522                             subpattern: Pat { span: pat.span, ty, kind: Box::new(kind), },
 523                         };
 524                     }
 525                 }
 526
 527                 kind
 528             }
 529
 530             hir::PatKind::Path(ref qpath) => {
 531                 return self.lower_path(qpath, pat.hir_id, pat.span);
 532             }
 533
 534             hir::PatKind::Ref(ref subpattern, _) |
 535             hir::PatKind::Box(ref subpattern) => {
 536                 PatKind::Deref { subpattern: self.lower_pattern(subpattern) }
 537             }
 538
 539             hir::PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 540                 match ty.kind {
 541                     ty::Ref(_, ty, _) =>
 542                         PatKind::Deref {
 543                             subpattern: Pat {
 544                                 ty,
 545                                 span: pat.span,
 546                                 kind: Box::new(self.slice_or_array_pattern(
 547                                     pat.span, ty, prefix, slice, suffix))
 548                             },
 549                         },
 550                     ty::Slice(..) |
 551                     ty::Array(..) =>
 552                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 553                     ty::Error => { // Avoid ICE
 554                         return Pat { span: pat.span, ty, kind: Box::new(PatKind::Wild) };
 555                     }
 556                     _ =>
 557                         span_bug!(
 558                             pat.span,
 559                             "unexpanded type for vector pattern: {:?}",
 560                             ty),
 561                 }
 562             }
 563
 564             hir::PatKind::Tuple(ref subpatterns, ddpos) => {
 565                 match ty.kind {
 566                     ty::Tuple(ref tys) => {
 567                         let subpatterns =
 568                             subpatterns.iter()
 569                                        .enumerate_and_adjust(tys.len(), ddpos)
 570                                        .map(|(i, subpattern)| FieldPat {
 571                                             field: Field::new(i),
 572                                             pattern: self.lower_pattern(subpattern)
 573                                        })
 574                                        .collect();
 575
 576                         PatKind::Leaf { subpatterns }
 577                     }
 578                     ty::Error => { // Avoid ICE (#50577)
 579                         return Pat { span: pat.span, ty, kind: Box::new(PatKind::Wild) };
 580                     }
 581                     _ => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", ty),
 582                 }
 583             }
 584
 585             hir::PatKind::Binding(_, id, ident, ref sub) => {
 586                 let var_ty = self.tables.node_type(pat.hir_id);
 587                 if let ty::Error = var_ty.kind {
 588                     // Avoid ICE
 589                     return Pat { span: pat.span, ty, kind: Box::new(PatKind::Wild) };
 590                 };
 591                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 592                                                          .expect("missing binding mode");
 593                 let (mutability, mode) = match bm {
 594                     ty::BindByValue(hir::MutMutable) =>
 595                         (Mutability::Mut, BindingMode::ByValue),
 596                     ty::BindByValue(hir::MutImmutable) =>
 597                         (Mutability::Not, BindingMode::ByValue),
 598                     ty::BindByReference(hir::MutMutable) =>
 599                         (Mutability::Not, BindingMode::ByRef(
 600                             BorrowKind::Mut { allow_two_phase_borrow: false })),
 601                     ty::BindByReference(hir::MutImmutable) =>
 602                         (Mutability::Not, BindingMode::ByRef(
 603                             BorrowKind::Shared)),
 604                 };
 605
 606                 // A ref x pattern is the same node used for x, and as such it has
 607                 // x's type, which is &T, where we want T (the type being matched).
 608                 if let ty::BindByReference(_) = bm {
 609                     if let ty::Ref(_, rty, _) = ty.kind {
 610                         ty = rty;
 611                     } else {
 612                         bug!("`ref {}` has wrong type {}", ident, ty);
 613                     }
 614                 }
 615
 616                 PatKind::Binding {
 617                     mutability,
 618                     mode,
 619                     name: ident.name,
 620                     var: id,
 621                     ty: var_ty,
 622                     subpattern: self.lower_opt_pattern(sub),
 623                 }
 624             }
 625
 626             hir::PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 627                 let res = self.tables.qpath_res(qpath, pat.hir_id);
 628                 let adt_def = match ty.kind {
 629                     ty::Adt(adt_def, _) => adt_def,
 630                     ty::Error => { // Avoid ICE (#50585)
 631                         return Pat { span: pat.span, ty, kind: Box::new(PatKind::Wild) };
 632                     }
 633                     _ => span_bug!(pat.span,
 634                                    "tuple struct pattern not applied to an ADT {:?}",
 635                                    ty),
 636                 };
 637                 let variant_def = adt_def.variant_of_res(res);
 638
 639                 let subpatterns =
 640                         subpatterns.iter()
 641                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 642                                    .map(|(i, field)| FieldPat {
 643                                        field: Field::new(i),
 644                                        pattern: self.lower_pattern(field),
 645                                    })
 646                     .collect();
 647
 648                 self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
 649             }
 650
 651             hir::PatKind::Struct(ref qpath, ref fields, _) => {
 652                 let res = self.tables.qpath_res(qpath, pat.hir_id);
 653                 let subpatterns =
 654                     fields.iter()
 655                           .map(|field| {
 656                               FieldPat {
 657                                   field: Field::new(self.tcx.field_index(field.hir_id,
 658                                                                          self.tables)),
 659                                   pattern: self.lower_pattern(&field.pat),
 660                               }
 661                           })
 662                           .collect();
 663
 664                 self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
 665             }
 666
 667             hir::PatKind::Or(ref pats) => {
 668                 PatKind::Or {
 669                     pats: pats.iter().map(|p| self.lower_pattern(p)).collect(),
 670                 }
 671             }
 672         };
 673
 674         Pat {
 675             span: pat.span,
 676             ty,
 677             kind: Box::new(kind),
 678         }
 679     }
 680
 681     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pat<'tcx>> {
 682         pats.iter().map(|p| self.lower_pattern(p)).collect()
 683     }
 684
 685     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pat<'tcx>>
 686     {
 687         pat.as_ref().map(|p| self.lower_pattern(p))
 688     }
 689
 690     fn flatten_nested_slice_patterns(
 691         &mut self,
 692         prefix: Vec<Pat<'tcx>>,
 693         slice: Option<Pat<'tcx>>,
 694         suffix: Vec<Pat<'tcx>>)
 695         -> (Vec<Pat<'tcx>>, Option<Pat<'tcx>>, Vec<Pat<'tcx>>)
 696     {
 697         let orig_slice = match slice {
 698             Some(orig_slice) => orig_slice,
 699             None => return (prefix, slice, suffix)
 700         };
 701         let orig_prefix = prefix;
 702         let orig_suffix = suffix;
 703
 704         // dance because of intentional borrow-checker stupidity.
 705         let kind = *orig_slice.kind;
 706         match kind {
 707             PatKind::Slice { prefix, slice, mut suffix } |
 708             PatKind::Array { prefix, slice, mut suffix } => {
 709                 let mut orig_prefix = orig_prefix;
 710
 711                 orig_prefix.extend(prefix);
 712                 suffix.extend(orig_suffix);
 713
 714                 (orig_prefix, slice, suffix)
 715             }
 716             _ => {
 717                 (orig_prefix, Some(Pat {
 718                     kind: box kind, ..orig_slice
 719                 }), orig_suffix)
 720             }
 721         }
 722     }
 723
 724     fn slice_or_array_pattern(
 725         &mut self,
 726         span: Span,
 727         ty: Ty<'tcx>,
 728         prefix: &'tcx [P<hir::Pat>],
 729         slice: &'tcx Option<P<hir::Pat>>,
 730         suffix: &'tcx [P<hir::Pat>])
 731         -> PatKind<'tcx>
 732     {
 733         let prefix = self.lower_patterns(prefix);
 734         let slice = self.lower_opt_pattern(slice);
 735         let suffix = self.lower_patterns(suffix);
 736         let (prefix, slice, suffix) =
 737             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 738
 739         match ty.kind {
 740             ty::Slice(..) => {
 741                 // matching a slice or fixed-length array
 742                 PatKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 743             }
 744
 745             ty::Array(_, len) => {
 746                 // fixed-length array
 747                 let len = len.eval_usize(self.tcx, self.param_env);
 748                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 749                 PatKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 750             }
 751
 752             _ => {
 753                 span_bug!(span, "bad slice pattern type {:?}", ty);
 754             }
 755         }
 756     }
 757
 758     fn lower_variant_or_leaf(
 759         &mut self,
 760         res: Res,
 761         hir_id: hir::HirId,
 762         span: Span,
 763         ty: Ty<'tcx>,
 764         subpatterns: Vec<FieldPat<'tcx>>,
 765     ) -> PatKind<'tcx> {
 766         let res = match res {
 767             Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_id) => {
 768                 let variant_id = self.tcx.parent(variant_ctor_id).unwrap();
 769                 Res::Def(DefKind::Variant, variant_id)
 770             },
 771             res => res,
 772         };
 773
 774         let mut kind = match res {
 775             Res::Def(DefKind::Variant, variant_id) => {
 776                 let enum_id = self.tcx.parent(variant_id).unwrap();
 777                 let adt_def = self.tcx.adt_def(enum_id);
 778                 if adt_def.is_enum() {
 779                     let substs = match ty.kind {
 780                         ty::Adt(_, substs) |
 781                         ty::FnDef(_, substs) => substs,
 782                         ty::Error => {  // Avoid ICE (#50585)
 783                             return PatKind::Wild;
 784                         }
 785                         _ => bug!("inappropriate type for def: {:?}", ty),
 786                     };
 787                     PatKind::Variant {
 788                         adt_def,
 789                         substs,
 790                         variant_index: adt_def.variant_index_with_id(variant_id),
 791                         subpatterns,
 792                     }
 793                 } else {
 794                     PatKind::Leaf { subpatterns }
 795                 }
 796             }
 797
 798             Res::Def(DefKind::Struct, _)
 799             | Res::Def(DefKind::Ctor(CtorOf::Struct, ..), _)
 800             | Res::Def(DefKind::Union, _)
 801             | Res::Def(DefKind::TyAlias, _)
 802             | Res::Def(DefKind::AssocTy, _)
 803             | Res::SelfTy(..)
 804             | Res::SelfCtor(..) => {
 805                 PatKind::Leaf { subpatterns }
 806             }
 807
 808             _ => {
 809                 self.errors.push(PatternError::NonConstPath(span));
 810                 PatKind::Wild
 811             }
 812         };
 813
 814         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 815             debug!("lower_variant_or_leaf: kind={:?} user_ty={:?} span={:?}", kind, user_ty, span);
 816             kind = PatKind::AscribeUserType {
 817                 subpattern: Pat {
 818                     span,
 819                     ty,
 820                     kind: Box::new(kind),
 821                 },
 822                 ascription: Ascription {
 823                     user_ty: PatTyProj::from_user_type(user_ty),
 824                     user_ty_span: span,
 825                     variance: ty::Variance::Covariant,
 826                 },
 827             };
 828         }
 829
 830         kind
 831     }
 832
 833     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 834     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 835     /// is converted to the corresponding pattern via `lower_variant_or_leaf`.
 836     fn lower_path(&mut self,
 837                   qpath: &hir::QPath,
 838                   id: hir::HirId,
 839                   span: Span)
 840                   -> Pat<'tcx> {
 841         let ty = self.tables.node_type(id);
 842         let res = self.tables.qpath_res(qpath, id);
 843         let is_associated_const = match res {
 844             Res::Def(DefKind::AssocConst, _) => true,
 845             _ => false,
 846         };
 847         let kind = match res {
 848             Res::Def(DefKind::Const, def_id) | Res::Def(DefKind::AssocConst, def_id) => {
 849                 let substs = self.tables.node_substs(id);
 850                 match ty::Instance::resolve(
 851                     self.tcx,
 852                     self.param_env,
 853                     def_id,
 854                     substs,
 855                 ) {
 856                     Some(instance) => {
 857                         let cid = GlobalId {
 858                             instance,
 859                             promoted: None,
 860                         };
 861                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 862                             Ok(value) => {
 863                                 let pattern = self.const_to_pat(value, id, span);
 864                                 if !is_associated_const {
 865                                     return pattern;
 866                                 }
 867
 868                                 let user_provided_types = self.tables().user_provided_types();
 869                                 return if let Some(u_ty) = user_provided_types.get(id) {
 870                                     let user_ty = PatTyProj::from_user_type(*u_ty);
 871                                     Pat {
 872                                         span,
 873                                         kind: Box::new(
 874                                             PatKind::AscribeUserType {
 875                                                 subpattern: pattern,
 876                                                 ascription: Ascription {
 877                                                     /// Note that use `Contravariant` here. See the
 878                                                     /// `variance` field documentation for details.
 879                                                     variance: ty::Variance::Contravariant,
 880                                                     user_ty,
 881                                                     user_ty_span: span,
 882                                                 },
 883                                             }
 884                                         ),
 885                                         ty: value.ty,
 886                                     }
 887                                 } else {
 888                                     pattern
 889                                 }
 890                             },
 891                             Err(_) => {
 892                                 self.tcx.sess.span_err(
 893                                     span,
 894                                     "could not evaluate constant pattern",
 895                                 );
 896                                 PatKind::Wild
 897                             }
 898                         }
 899                     },
 900                     None => {
 901                         self.errors.push(if is_associated_const {
 902                             PatternError::AssocConstInPattern(span)
 903                         } else {
 904                             PatternError::StaticInPattern(span)
 905                         });
 906                         PatKind::Wild
 907                     },
 908                 }
 909             }
 910             _ => self.lower_variant_or_leaf(res, id, span, ty, vec![]),
 911         };
 912
 913         Pat {
 914             span,
 915             ty,
 916             kind: Box::new(kind),
 917         }
 918     }
 919
 920     /// Converts literals, paths and negation of literals to patterns.
 921     /// The special case for negation exists to allow things like `-128_i8`
 922     /// which would overflow if we tried to evaluate `128_i8` and then negate
 923     /// afterwards.
 924     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatKind<'tcx> {
 925         match expr.kind {
 926             hir::ExprKind::Lit(ref lit) => {
 927                 let ty = self.tables.expr_ty(expr);
 928                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 929                     Ok(val) => {
 930                         *self.const_to_pat(val, expr.hir_id, lit.span).kind
 931                     },
 932                     Err(LitToConstError::UnparseableFloat) => {
 933                         self.errors.push(PatternError::FloatBug);
 934                         PatKind::Wild
 935                     },
 936                     Err(LitToConstError::Reported) => PatKind::Wild,
 937                 }
 938             },
 939             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 940             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 941                 let ty = self.tables.expr_ty(expr);
 942                 let lit = match expr.kind {
 943                     hir::ExprKind::Lit(ref lit) => lit,
 944                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 945                 };
 946                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 947                     Ok(val) => {
 948                         *self.const_to_pat(val, expr.hir_id, lit.span).kind
 949                     },
 950                     Err(LitToConstError::UnparseableFloat) => {
 951                         self.errors.push(PatternError::FloatBug);
 952                         PatKind::Wild
 953                     },
 954                     Err(LitToConstError::Reported) => PatKind::Wild,
 955                 }
 956             }
 957             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 958         }
 959     }
 960 }
 961
 962 impl UserAnnotatedTyHelpers<'tcx> for PatCtxt<'_, 'tcx> {
 963     fn tcx(&self) -> TyCtxt<'tcx> {
 964         self.tcx
 965     }
 966
 967     fn tables(&self) -> &ty::TypeckTables<'tcx> {
 968         self.tables
 969     }
 970 }
 971
 972
 973 pub trait PatternFoldable<'tcx> : Sized {
 974     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 975         self.super_fold_with(folder)
 976     }
 977
 978     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
 979 }
 980
 981 pub trait PatternFolder<'tcx> : Sized {
 982     fn fold_pattern(&mut self, pattern: &Pat<'tcx>) -> Pat<'tcx> {
 983         pattern.super_fold_with(self)
 984     }
 985
 986     fn fold_pattern_kind(&mut self, kind: &PatKind<'tcx>) -> PatKind<'tcx> {
 987         kind.super_fold_with(self)
 988     }
 989 }
 990
 991
 992 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
 993     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 994         let content: T = (**self).fold_with(folder);
 995         box content
 996     }
 997 }
 998
 999 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1000     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1001         self.iter().map(|t| t.fold_with(folder)).collect()
1002     }
1003 }
1004
1005 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1006     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1007         self.as_ref().map(|t| t.fold_with(folder))
1008     }
1009 }
1010
1011 macro_rules! CloneImpls {
1012     (<$lt_tcx:tt> $($ty:ty),+) => {
1013         $(
1014             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1015                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1016                     Clone::clone(self)
1017                 }
1018             }
1019         )+
1020     }
1021 }
1022
1023 CloneImpls!{ <'tcx>
1024     Span, Field, Mutability, ast::Name, hir::HirId, usize, ty::Const<'tcx>,
1025     Region<'tcx>, Ty<'tcx>, BindingMode, &'tcx AdtDef,
1026     SubstsRef<'tcx>, &'tcx GenericArg<'tcx>, UserType<'tcx>,
1027     UserTypeProjection, PatTyProj<'tcx>
1028 }
1029
1030 impl<'tcx> PatternFoldable<'tcx> for FieldPat<'tcx> {
1031     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1032         FieldPat {
1033             field: self.field.fold_with(folder),
1034             pattern: self.pattern.fold_with(folder)
1035         }
1036     }
1037 }
1038
1039 impl<'tcx> PatternFoldable<'tcx> for Pat<'tcx> {
1040     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1041         folder.fold_pattern(self)
1042     }
1043
1044     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1045         Pat {
1046             ty: self.ty.fold_with(folder),
1047             span: self.span.fold_with(folder),
1048             kind: self.kind.fold_with(folder)
1049         }
1050     }
1051 }
1052
1053 impl<'tcx> PatternFoldable<'tcx> for PatKind<'tcx> {
1054     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1055         folder.fold_pattern_kind(self)
1056     }
1057
1058     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1059         match *self {
1060             PatKind::Wild => PatKind::Wild,
1061             PatKind::AscribeUserType {
1062                 ref subpattern,
1063                 ascription: Ascription {
1064                     variance,
1065                     ref user_ty,
1066                     user_ty_span,
1067                 },
1068             } => PatKind::AscribeUserType {
1069                 subpattern: subpattern.fold_with(folder),
1070                 ascription: Ascription {
1071                     user_ty: user_ty.fold_with(folder),
1072                     variance,
1073                     user_ty_span,
1074                 },
1075             },
1076             PatKind::Binding {
1077                 mutability,
1078                 name,
1079                 mode,
1080                 var,
1081                 ty,
1082                 ref subpattern,
1083             } => PatKind::Binding {
1084                 mutability: mutability.fold_with(folder),
1085                 name: name.fold_with(folder),
1086                 mode: mode.fold_with(folder),
1087                 var: var.fold_with(folder),
1088                 ty: ty.fold_with(folder),
1089                 subpattern: subpattern.fold_with(folder),
1090             },
1091             PatKind::Variant {
1092                 adt_def,
1093                 substs,
1094                 variant_index,
1095                 ref subpatterns,
1096             } => PatKind::Variant {
1097                 adt_def: adt_def.fold_with(folder),
1098                 substs: substs.fold_with(folder),
1099                 variant_index,
1100                 subpatterns: subpatterns.fold_with(folder)
1101             },
1102             PatKind::Leaf {
1103                 ref subpatterns,
1104             } => PatKind::Leaf {
1105                 subpatterns: subpatterns.fold_with(folder),
1106             },
1107             PatKind::Deref {
1108                 ref subpattern,
1109             } => PatKind::Deref {
1110                 subpattern: subpattern.fold_with(folder),
1111             },
1112             PatKind::Constant {
1113                 value
1114             } => PatKind::Constant {
1115                 value,
1116             },
1117             PatKind::Range(range) => PatKind::Range(range),
1118             PatKind::Slice {
1119                 ref prefix,
1120                 ref slice,
1121                 ref suffix,
1122             } => PatKind::Slice {
1123                 prefix: prefix.fold_with(folder),
1124                 slice: slice.fold_with(folder),
1125                 suffix: suffix.fold_with(folder)
1126             },
1127             PatKind::Array {
1128                 ref prefix,
1129                 ref slice,
1130                 ref suffix
1131             } => PatKind::Array {
1132                 prefix: prefix.fold_with(folder),
1133                 slice: slice.fold_with(folder),
1134                 suffix: suffix.fold_with(folder)
1135             },
1136             PatKind::Or { ref pats } => PatKind::Or { pats: pats.fold_with(folder) },
1137         }
1138     }
1139 }
1140
1141 pub fn compare_const_vals<'tcx>(
1142     tcx: TyCtxt<'tcx>,
1143     a: &'tcx ty::Const<'tcx>,
1144     b: &'tcx ty::Const<'tcx>,
1145     param_env: ty::ParamEnv<'tcx>,
1146     ty: Ty<'tcx>,
1147 ) -> Option<Ordering> {
1148     trace!("compare_const_vals: {:?}, {:?}", a, b);
1149
1150     let from_bool = |v: bool| {
1151         if v {
1152             Some(Ordering::Equal)
1153         } else {
1154             None
1155         }
1156     };
1157
1158     let fallback = || from_bool(a == b);
1159
1160     // Use the fallback if any type differs
1161     if a.ty != b.ty || a.ty != ty {
1162         return fallback();
1163     }
1164
1165     let a_bits = a.try_eval_bits(tcx, param_env, ty);
1166     let b_bits = b.try_eval_bits(tcx, param_env, ty);
1167
1168     if let (Some(a), Some(b)) = (a_bits, b_bits) {
1169         use ::rustc_apfloat::Float;
1170         return match ty.kind {
1171             ty::Float(ast::FloatTy::F32) => {
1172                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1173                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1174                 l.partial_cmp(&r)
1175             }
1176             ty::Float(ast::FloatTy::F64) => {
1177                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1178                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1179                 l.partial_cmp(&r)
1180             }
1181             ty::Int(ity) => {
1182                 use rustc::ty::layout::{Integer, IntegerExt};
1183                 use syntax::attr::SignedInt;
1184                 let size = Integer::from_attr(&tcx, SignedInt(ity)).size();
1185                 let a = sign_extend(a, size);
1186                 let b = sign_extend(b, size);
1187                 Some((a as i128).cmp(&(b as i128)))
1188             }
1189             _ => Some(a.cmp(&b)),
1190         }
1191     }
1192
1193     if let ty::Str = ty.kind {
1194         match (a.val, b.val) {
1195             (ConstValue::Slice { .. }, ConstValue::Slice { .. }) => {
1196                 let a_bytes = get_slice_bytes(&tcx, a.val);
1197                 let b_bytes = get_slice_bytes(&tcx, b.val);
1198                 return from_bool(a_bytes == b_bytes);
1199             }
1200             _ => (),
1201         }
1202     }
1203
1204     fallback()
1205 }