src/librustc_mir/hair/pattern/mod.rs

   1 //! Validation of patterns/matches.
   2
   3 mod _match;
   4 mod check_match;
   5
   6 pub(crate) use self::check_match::check_match;
   7
   8 use crate::const_eval::{const_field, const_variant_index};
   9
  10 use crate::hair::util::UserAnnotatedTyHelpers;
  11 use crate::hair::constant::*;
  12
  13 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability};
  14 use rustc::mir::{UserTypeProjection};
  15 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  16 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, UserType, DefIdTree};
  17 use rustc::ty::{CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations};
  18 use rustc::ty::subst::{SubstsRef, Kind};
  19 use rustc::ty::layout::VariantIdx;
  20 use rustc::hir::{self, PatKind, RangeEnd};
  21 use rustc::hir::def::{CtorOf, Res, DefKind, CtorKind};
  22 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  23
  24 use rustc_data_structures::indexed_vec::Idx;
  25
  26 use std::cmp::Ordering;
  27 use std::fmt;
  28 use syntax::ast;
  29 use syntax::ptr::P;
  30 use syntax_pos::Span;
  31
  32 #[derive(Clone, Debug)]
  33 pub enum PatternError {
  34     AssociatedConstInPattern(Span),
  35     StaticInPattern(Span),
  36     FloatBug,
  37     NonConstPath(Span),
  38 }
  39
  40 #[derive(Copy, Clone, Debug)]
  41 pub enum BindingMode {
  42     ByValue,
  43     ByRef(BorrowKind),
  44 }
  45
  46 #[derive(Clone, Debug)]
  47 pub struct FieldPattern<'tcx> {
  48     pub field: Field,
  49     pub pattern: Pattern<'tcx>,
  50 }
  51
  52 #[derive(Clone, Debug)]
  53 pub struct Pattern<'tcx> {
  54     pub ty: Ty<'tcx>,
  55     pub span: Span,
  56     pub kind: Box<PatternKind<'tcx>>,
  57 }
  58
  59
  60 #[derive(Copy, Clone, Debug, PartialEq)]
  61 pub struct PatternTypeProjection<'tcx> {
  62     pub user_ty: CanonicalUserType<'tcx>,
  63 }
  64
  65 impl<'tcx> PatternTypeProjection<'tcx> {
  66     pub(crate) fn from_user_type(user_annotation: CanonicalUserType<'tcx>) -> Self {
  67         Self {
  68             user_ty: user_annotation,
  69         }
  70     }
  71
  72     pub(crate) fn user_ty(
  73         self,
  74         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
  75         inferred_ty: Ty<'tcx>,
  76         span: Span,
  77     ) -> UserTypeProjection {
  78         UserTypeProjection {
  79             base: annotations.push(CanonicalUserTypeAnnotation {
  80                 span,
  81                 user_ty: self.user_ty,
  82                 inferred_ty,
  83             }),
  84             projs: Vec::new(),
  85         }
  86     }
  87 }
  88
  89 #[derive(Copy, Clone, Debug, PartialEq)]
  90 pub struct Ascription<'tcx> {
  91     pub user_ty: PatternTypeProjection<'tcx>,
  92     /// Variance to use when relating the type `user_ty` to the **type of the value being
  93     /// matched**. Typically, this is `Variance::Covariant`, since the value being matched must
  94     /// have a type that is some subtype of the ascribed type.
  95     ///
  96     /// Note that this variance does not apply for any bindings within subpatterns. The type
  97     /// assigned to those bindings must be exactly equal to the `user_ty` given here.
  98     ///
  99     /// The only place where this field is not `Covariant` is when matching constants, where
 100     /// we currently use `Contravariant` -- this is because the constant type just needs to
 101     /// be "comparable" to the type of the input value. So, for example:
 102     ///
 103     /// ```text
 104     /// match x { "foo" => .. }
 105     /// ```
 106     ///
 107     /// requires that `&'static str <: T_x`, where `T_x` is the type of `x`. Really, we should
 108     /// probably be checking for a `PartialEq` impl instead, but this preserves the behavior
 109     /// of the old type-check for now. See #57280 for details.
 110     pub variance: ty::Variance,
 111     pub user_ty_span: Span,
 112 }
 113
 114 #[derive(Clone, Debug)]
 115 pub enum PatternKind<'tcx> {
 116     Wild,
 117
 118     AscribeUserType {
 119         ascription: Ascription<'tcx>,
 120         subpattern: Pattern<'tcx>,
 121     },
 122
 123     /// `x`, `ref x`, `x @ P`, etc.
 124     Binding {
 125         mutability: Mutability,
 126         name: ast::Name,
 127         mode: BindingMode,
 128         var: hir::HirId,
 129         ty: Ty<'tcx>,
 130         subpattern: Option<Pattern<'tcx>>,
 131     },
 132
 133     /// `Foo(...)` or `Foo{...}` or `Foo`, where `Foo` is a variant name from an ADT with
 134     /// multiple variants.
 135     Variant {
 136         adt_def: &'tcx AdtDef,
 137         substs: SubstsRef<'tcx>,
 138         variant_index: VariantIdx,
 139         subpatterns: Vec<FieldPattern<'tcx>>,
 140     },
 141
 142     /// `(...)`, `Foo(...)`, `Foo{...}`, or `Foo`, where `Foo` is a variant name from an ADT with
 143     /// a single variant.
 144     Leaf {
 145         subpatterns: Vec<FieldPattern<'tcx>>,
 146     },
 147
 148     /// `box P`, `&P`, `&mut P`, etc.
 149     Deref {
 150         subpattern: Pattern<'tcx>,
 151     },
 152
 153     Constant {
 154         value: ty::Const<'tcx>,
 155     },
 156
 157     Range(PatternRange<'tcx>),
 158
 159     /// Matches against a slice, checking the length and extracting elements.
 160     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 161     /// e.g., `&[ref xs..]`.
 162     Slice {
 163         prefix: Vec<Pattern<'tcx>>,
 164         slice: Option<Pattern<'tcx>>,
 165         suffix: Vec<Pattern<'tcx>>,
 166     },
 167
 168     /// Fixed match against an array; irrefutable.
 169     Array {
 170         prefix: Vec<Pattern<'tcx>>,
 171         slice: Option<Pattern<'tcx>>,
 172         suffix: Vec<Pattern<'tcx>>,
 173     },
 174 }
 175
 176 #[derive(Copy, Clone, Debug, PartialEq)]
 177 pub struct PatternRange<'tcx> {
 178     pub lo: ty::Const<'tcx>,
 179     pub hi: ty::Const<'tcx>,
 180     pub ty: Ty<'tcx>,
 181     pub end: RangeEnd,
 182 }
 183
 184 impl<'tcx> fmt::Display for Pattern<'tcx> {
 185     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 186         match *self.kind {
 187             PatternKind::Wild => write!(f, "_"),
 188             PatternKind::AscribeUserType { ref subpattern, .. } =>
 189                 write!(f, "{}: _", subpattern),
 190             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 191                 let is_mut = match mode {
 192                     BindingMode::ByValue => mutability == Mutability::Mut,
 193                     BindingMode::ByRef(bk) => {
 194                         write!(f, "ref ")?;
 195                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 196                     }
 197                 };
 198                 if is_mut {
 199                     write!(f, "mut ")?;
 200                 }
 201                 write!(f, "{}", name)?;
 202                 if let Some(ref subpattern) = *subpattern {
 203                     write!(f, " @ {}", subpattern)?;
 204                 }
 205                 Ok(())
 206             }
 207             PatternKind::Variant { ref subpatterns, .. } |
 208             PatternKind::Leaf { ref subpatterns } => {
 209                 let variant = match *self.kind {
 210                     PatternKind::Variant { adt_def, variant_index, .. } => {
 211                         Some(&adt_def.variants[variant_index])
 212                     }
 213                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 214                         if !adt.is_enum() {
 215                             Some(&adt.variants[VariantIdx::new(0)])
 216                         } else {
 217                             None
 218                         }
 219                     } else {
 220                         None
 221                     }
 222                 };
 223
 224                 let mut first = true;
 225                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 226
 227                 if let Some(variant) = variant {
 228                     write!(f, "{}", variant.ident)?;
 229
 230                     // Only for Adt we can have `S {...}`,
 231                     // which we handle separately here.
 232                     if variant.ctor_kind == CtorKind::Fictive {
 233                         write!(f, " {{ ")?;
 234
 235                         let mut printed = 0;
 236                         for p in subpatterns {
 237                             if let PatternKind::Wild = *p.pattern.kind {
 238                                 continue;
 239                             }
 240                             let name = variant.fields[p.field.index()].ident;
 241                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 242                             printed += 1;
 243                         }
 244
 245                         if printed < variant.fields.len() {
 246                             write!(f, "{}..", start_or_continue())?;
 247                         }
 248
 249                         return write!(f, " }}");
 250                     }
 251                 }
 252
 253                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 254                 if num_fields != 0 || variant.is_none() {
 255                     write!(f, "(")?;
 256                     for i in 0..num_fields {
 257                         write!(f, "{}", start_or_continue())?;
 258
 259                         // Common case: the field is where we expect it.
 260                         if let Some(p) = subpatterns.get(i) {
 261                             if p.field.index() == i {
 262                                 write!(f, "{}", p.pattern)?;
 263                                 continue;
 264                             }
 265                         }
 266
 267                         // Otherwise, we have to go looking for it.
 268                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 269                             write!(f, "{}", p.pattern)?;
 270                         } else {
 271                             write!(f, "_")?;
 272                         }
 273                     }
 274                     write!(f, ")")?;
 275                 }
 276
 277                 Ok(())
 278             }
 279             PatternKind::Deref { ref subpattern } => {
 280                 match self.ty.sty {
 281                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 282                     ty::Ref(_, _, mutbl) => {
 283                         write!(f, "&")?;
 284                         if mutbl == hir::MutMutable {
 285                             write!(f, "mut ")?;
 286                         }
 287                     }
 288                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 289                 }
 290                 write!(f, "{}", subpattern)
 291             }
 292             PatternKind::Constant { value } => {
 293                 fmt_const_val(f, value)
 294             }
 295             PatternKind::Range(PatternRange { lo, hi, ty: _, end }) => {
 296                 fmt_const_val(f, lo)?;
 297                 match end {
 298                     RangeEnd::Included => write!(f, "..=")?,
 299                     RangeEnd::Excluded => write!(f, "..")?,
 300                 }
 301                 fmt_const_val(f, hi)
 302             }
 303             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 304             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 305                 let mut first = true;
 306                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 307                 write!(f, "[")?;
 308                 for p in prefix {
 309                     write!(f, "{}{}", start_or_continue(), p)?;
 310                 }
 311                 if let Some(ref slice) = *slice {
 312                     write!(f, "{}", start_or_continue())?;
 313                     match *slice.kind {
 314                         PatternKind::Wild => {}
 315                         _ => write!(f, "{}", slice)?
 316                     }
 317                     write!(f, "..")?;
 318                 }
 319                 for p in suffix {
 320                     write!(f, "{}{}", start_or_continue(), p)?;
 321                 }
 322                 write!(f, "]")
 323             }
 324         }
 325     }
 326 }
 327
 328 pub struct PatternContext<'a, 'tcx: 'a> {
 329     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 330     pub param_env: ty::ParamEnv<'tcx>,
 331     pub tables: &'a ty::TypeckTables<'tcx>,
 332     pub substs: SubstsRef<'tcx>,
 333     pub errors: Vec<PatternError>,
 334 }
 335
 336 impl<'a, 'tcx> Pattern<'tcx> {
 337     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 338                     param_env_and_substs: ty::ParamEnvAnd<'tcx, SubstsRef<'tcx>>,
 339                     tables: &'a ty::TypeckTables<'tcx>,
 340                     pat: &'tcx hir::Pat) -> Self {
 341         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 342         let result = pcx.lower_pattern(pat);
 343         if !pcx.errors.is_empty() {
 344             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 345             tcx.sess.delay_span_bug(pat.span, &msg);
 346         }
 347         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 348         result
 349     }
 350 }
 351
 352 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 353     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 354                param_env_and_substs: ty::ParamEnvAnd<'tcx, SubstsRef<'tcx>>,
 355                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 356         PatternContext {
 357             tcx,
 358             param_env: param_env_and_substs.param_env,
 359             tables,
 360             substs: param_env_and_substs.value,
 361             errors: vec![]
 362         }
 363     }
 364
 365     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 366         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 367         // pattern has the type that results *after* dereferencing. For example, in this code:
 368         //
 369         // ```
 370         // match &&Some(0i32) {
 371         //     Some(n) => { ... },
 372         //     _ => { ... },
 373         // }
 374         // ```
 375         //
 376         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 377         // determined in rustc_typeck::check::match). The adjustments would be
 378         //
 379         // `vec![&&Option<i32>, &Option<i32>]`.
 380         //
 381         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 382         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 383         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 384         // gets the least-dereferenced type).
 385         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 386         self.tables
 387             .pat_adjustments()
 388             .get(pat.hir_id)
 389             .unwrap_or(&vec![])
 390             .iter()
 391             .rev()
 392             .fold(unadjusted_pat, |pat, ref_ty| {
 393                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 394                     Pattern {
 395                         span: pat.span,
 396                         ty: ref_ty,
 397                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 398                     }
 399                 },
 400             )
 401     }
 402
 403     fn lower_range_expr(
 404         &mut self,
 405         expr: &'tcx hir::Expr,
 406     ) -> (PatternKind<'tcx>, Option<Ascription<'tcx>>) {
 407         match self.lower_lit(expr) {
 408             PatternKind::AscribeUserType {
 409                 ascription: lo_ascription,
 410                 subpattern: Pattern { kind: box kind, .. },
 411             } => (kind, Some(lo_ascription)),
 412             kind => (kind, None),
 413         }
 414     }
 415
 416     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 417         let mut ty = self.tables.node_type(pat.hir_id);
 418
 419         let kind = match pat.node {
 420             PatKind::Wild => PatternKind::Wild,
 421
 422             PatKind::Lit(ref value) => self.lower_lit(value),
 423
 424             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 425                 let (lo, lo_ascription) = self.lower_range_expr(lo_expr);
 426                 let (hi, hi_ascription) = self.lower_range_expr(hi_expr);
 427
 428                 let mut kind = match (lo, hi) {
 429                     (PatternKind::Constant { value: lo }, PatternKind::Constant { value: hi }) => {
 430                         let cmp = compare_const_vals(
 431                             self.tcx,
 432                             lo,
 433                             hi,
 434                             self.param_env.and(ty),
 435                         );
 436                         match (end, cmp) {
 437                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 438                                 PatternKind::Range(PatternRange { lo, hi, ty, end }),
 439                             (RangeEnd::Excluded, _) => {
 440                                 span_err!(
 441                                     self.tcx.sess,
 442                                     lo_expr.span,
 443                                     E0579,
 444                                     "lower range bound must be less than upper",
 445                                 );
 446                                 PatternKind::Wild
 447                             }
 448                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 449                                 PatternKind::Constant { value: lo }
 450                             }
 451                             (RangeEnd::Included, Some(Ordering::Less)) => {
 452                                 PatternKind::Range(PatternRange { lo, hi, ty, end })
 453                             }
 454                             (RangeEnd::Included, _) => {
 455                                 let mut err = struct_span_err!(
 456                                     self.tcx.sess,
 457                                     lo_expr.span,
 458                                     E0030,
 459                                     "lower range bound must be less than or equal to upper"
 460                                 );
 461                                 err.span_label(
 462                                     lo_expr.span,
 463                                     "lower bound larger than upper bound",
 464                                 );
 465                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 466                                     err.note("When matching against a range, the compiler \
 467                                               verifies that the range is non-empty. Range \
 468                                               patterns include both end-points, so this is \
 469                                               equivalent to requiring the start of the range \
 470                                               to be less than or equal to the end of the range.");
 471                                 }
 472                                 err.emit();
 473                                 PatternKind::Wild
 474                             }
 475                         }
 476                     },
 477                     ref pats => {
 478                         self.tcx.sess.delay_span_bug(
 479                             pat.span,
 480                             &format!(
 481                                 "found bad range pattern `{:?}` outside of error recovery",
 482                                 pats,
 483                             ),
 484                         );
 485
 486                         PatternKind::Wild
 487                     },
 488                 };
 489
 490                 // If we are handling a range with associated constants (e.g.
 491                 // `Foo::<'a>::A..=Foo::B`), we need to put the ascriptions for the associated
 492                 // constants somewhere. Have them on the range pattern.
 493                 for ascription in &[lo_ascription, hi_ascription] {
 494                     if let Some(ascription) = ascription {
 495                         kind = PatternKind::AscribeUserType {
 496                             ascription: *ascription,
 497                             subpattern: Pattern { span: pat.span, ty, kind: Box::new(kind), },
 498                         };
 499                     }
 500                 }
 501
 502                 kind
 503             }
 504
 505             PatKind::Path(ref qpath) => {
 506                 return self.lower_path(qpath, pat.hir_id, pat.span);
 507             }
 508
 509             PatKind::Ref(ref subpattern, _) |
 510             PatKind::Box(ref subpattern) => {
 511                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 512             }
 513
 514             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 515                 match ty.sty {
 516                     ty::Ref(_, ty, _) =>
 517                         PatternKind::Deref {
 518                             subpattern: Pattern {
 519                                 ty,
 520                                 span: pat.span,
 521                                 kind: Box::new(self.slice_or_array_pattern(
 522                                     pat.span, ty, prefix, slice, suffix))
 523                             },
 524                         },
 525                     ty::Slice(..) |
 526                     ty::Array(..) =>
 527                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 528                     ty::Error => { // Avoid ICE
 529                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 530                     }
 531                     _ =>
 532                         span_bug!(
 533                             pat.span,
 534                             "unexpanded type for vector pattern: {:?}",
 535                             ty),
 536                 }
 537             }
 538
 539             PatKind::Tuple(ref subpatterns, ddpos) => {
 540                 match ty.sty {
 541                     ty::Tuple(ref tys) => {
 542                         let subpatterns =
 543                             subpatterns.iter()
 544                                        .enumerate_and_adjust(tys.len(), ddpos)
 545                                        .map(|(i, subpattern)| FieldPattern {
 546                                             field: Field::new(i),
 547                                             pattern: self.lower_pattern(subpattern)
 548                                        })
 549                                        .collect();
 550
 551                         PatternKind::Leaf { subpatterns }
 552                     }
 553                     ty::Error => { // Avoid ICE (#50577)
 554                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 555                     }
 556                     _ => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", ty),
 557                 }
 558             }
 559
 560             PatKind::Binding(_, id, ident, ref sub) => {
 561                 let var_ty = self.tables.node_type(pat.hir_id);
 562                 if let ty::Error = var_ty.sty {
 563                     // Avoid ICE
 564                     return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 565                 };
 566                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 567                                                          .expect("missing binding mode");
 568                 let (mutability, mode) = match bm {
 569                     ty::BindByValue(hir::MutMutable) =>
 570                         (Mutability::Mut, BindingMode::ByValue),
 571                     ty::BindByValue(hir::MutImmutable) =>
 572                         (Mutability::Not, BindingMode::ByValue),
 573                     ty::BindByReference(hir::MutMutable) =>
 574                         (Mutability::Not, BindingMode::ByRef(
 575                             BorrowKind::Mut { allow_two_phase_borrow: false })),
 576                     ty::BindByReference(hir::MutImmutable) =>
 577                         (Mutability::Not, BindingMode::ByRef(
 578                             BorrowKind::Shared)),
 579                 };
 580
 581                 // A ref x pattern is the same node used for x, and as such it has
 582                 // x's type, which is &T, where we want T (the type being matched).
 583                 if let ty::BindByReference(_) = bm {
 584                     if let ty::Ref(_, rty, _) = ty.sty {
 585                         ty = rty;
 586                     } else {
 587                         bug!("`ref {}` has wrong type {}", ident, ty);
 588                     }
 589                 }
 590
 591                 PatternKind::Binding {
 592                     mutability,
 593                     mode,
 594                     name: ident.name,
 595                     var: id,
 596                     ty: var_ty,
 597                     subpattern: self.lower_opt_pattern(sub),
 598                 }
 599             }
 600
 601             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 602                 let res = self.tables.qpath_res(qpath, pat.hir_id);
 603                 let adt_def = match ty.sty {
 604                     ty::Adt(adt_def, _) => adt_def,
 605                     ty::Error => { // Avoid ICE (#50585)
 606                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 607                     }
 608                     _ => span_bug!(pat.span,
 609                                    "tuple struct pattern not applied to an ADT {:?}",
 610                                    ty),
 611                 };
 612                 let variant_def = adt_def.variant_of_res(res);
 613
 614                 let subpatterns =
 615                         subpatterns.iter()
 616                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 617                                    .map(|(i, field)| FieldPattern {
 618                                        field: Field::new(i),
 619                                        pattern: self.lower_pattern(field),
 620                                    })
 621                     .collect();
 622
 623                 self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
 624             }
 625
 626             PatKind::Struct(ref qpath, ref fields, _) => {
 627                 let res = self.tables.qpath_res(qpath, pat.hir_id);
 628                 let subpatterns =
 629                     fields.iter()
 630                           .map(|field| {
 631                               FieldPattern {
 632                                   field: Field::new(self.tcx.field_index(field.node.hir_id,
 633                                                                          self.tables)),
 634                                   pattern: self.lower_pattern(&field.node.pat),
 635                               }
 636                           })
 637                           .collect();
 638
 639                 self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
 640             }
 641         };
 642
 643         Pattern {
 644             span: pat.span,
 645             ty,
 646             kind: Box::new(kind),
 647         }
 648     }
 649
 650     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 651         pats.iter().map(|p| self.lower_pattern(p)).collect()
 652     }
 653
 654     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 655     {
 656         pat.as_ref().map(|p| self.lower_pattern(p))
 657     }
 658
 659     fn flatten_nested_slice_patterns(
 660         &mut self,
 661         prefix: Vec<Pattern<'tcx>>,
 662         slice: Option<Pattern<'tcx>>,
 663         suffix: Vec<Pattern<'tcx>>)
 664         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 665     {
 666         let orig_slice = match slice {
 667             Some(orig_slice) => orig_slice,
 668             None => return (prefix, slice, suffix)
 669         };
 670         let orig_prefix = prefix;
 671         let orig_suffix = suffix;
 672
 673         // dance because of intentional borrow-checker stupidity.
 674         let kind = *orig_slice.kind;
 675         match kind {
 676             PatternKind::Slice { prefix, slice, mut suffix } |
 677             PatternKind::Array { prefix, slice, mut suffix } => {
 678                 let mut orig_prefix = orig_prefix;
 679
 680                 orig_prefix.extend(prefix);
 681                 suffix.extend(orig_suffix);
 682
 683                 (orig_prefix, slice, suffix)
 684             }
 685             _ => {
 686                 (orig_prefix, Some(Pattern {
 687                     kind: box kind, ..orig_slice
 688                 }), orig_suffix)
 689             }
 690         }
 691     }
 692
 693     fn slice_or_array_pattern(
 694         &mut self,
 695         span: Span,
 696         ty: Ty<'tcx>,
 697         prefix: &'tcx [P<hir::Pat>],
 698         slice: &'tcx Option<P<hir::Pat>>,
 699         suffix: &'tcx [P<hir::Pat>])
 700         -> PatternKind<'tcx>
 701     {
 702         let prefix = self.lower_patterns(prefix);
 703         let slice = self.lower_opt_pattern(slice);
 704         let suffix = self.lower_patterns(suffix);
 705         let (prefix, slice, suffix) =
 706             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 707
 708         match ty.sty {
 709             ty::Slice(..) => {
 710                 // matching a slice or fixed-length array
 711                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 712             }
 713
 714             ty::Array(_, len) => {
 715                 // fixed-length array
 716                 let len = len.unwrap_usize(self.tcx);
 717                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 718                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 719             }
 720
 721             _ => {
 722                 span_bug!(span, "bad slice pattern type {:?}", ty);
 723             }
 724         }
 725     }
 726
 727     fn lower_variant_or_leaf(
 728         &mut self,
 729         res: Res,
 730         hir_id: hir::HirId,
 731         span: Span,
 732         ty: Ty<'tcx>,
 733         subpatterns: Vec<FieldPattern<'tcx>>,
 734     ) -> PatternKind<'tcx> {
 735         let res = match res {
 736             Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_id) => {
 737                 let variant_id = self.tcx.parent(variant_ctor_id).unwrap();
 738                 Res::Def(DefKind::Variant, variant_id)
 739             },
 740             res => res,
 741         };
 742
 743         let mut kind = match res {
 744             Res::Def(DefKind::Variant, variant_id) => {
 745                 let enum_id = self.tcx.parent(variant_id).unwrap();
 746                 let adt_def = self.tcx.adt_def(enum_id);
 747                 if adt_def.is_enum() {
 748                     let substs = match ty.sty {
 749                         ty::Adt(_, substs) |
 750                         ty::FnDef(_, substs) => substs,
 751                         ty::Error => {  // Avoid ICE (#50585)
 752                             return PatternKind::Wild;
 753                         }
 754                         _ => bug!("inappropriate type for def: {:?}", ty),
 755                     };
 756                     PatternKind::Variant {
 757                         adt_def,
 758                         substs,
 759                         variant_index: adt_def.variant_index_with_id(variant_id),
 760                         subpatterns,
 761                     }
 762                 } else {
 763                     PatternKind::Leaf { subpatterns }
 764                 }
 765             }
 766
 767             Res::Def(DefKind::Struct, _)
 768             | Res::Def(DefKind::Ctor(CtorOf::Struct, ..), _)
 769             | Res::Def(DefKind::Union, _)
 770             | Res::Def(DefKind::TyAlias, _)
 771             | Res::Def(DefKind::AssociatedTy, _)
 772             | Res::SelfTy(..)
 773             | Res::SelfCtor(..) => {
 774                 PatternKind::Leaf { subpatterns }
 775             }
 776
 777             _ => {
 778                 self.errors.push(PatternError::NonConstPath(span));
 779                 PatternKind::Wild
 780             }
 781         };
 782
 783         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 784             debug!("lower_variant_or_leaf: kind={:?} user_ty={:?} span={:?}", kind, user_ty, span);
 785             kind = PatternKind::AscribeUserType {
 786                 subpattern: Pattern {
 787                     span,
 788                     ty,
 789                     kind: Box::new(kind),
 790                 },
 791                 ascription: Ascription {
 792                     user_ty: PatternTypeProjection::from_user_type(user_ty),
 793                     user_ty_span: span,
 794                     variance: ty::Variance::Covariant,
 795                 },
 796             };
 797         }
 798
 799         kind
 800     }
 801
 802     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 803     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 804     /// is converted to the corresponding pattern via `lower_variant_or_leaf`.
 805     fn lower_path(&mut self,
 806                   qpath: &hir::QPath,
 807                   id: hir::HirId,
 808                   span: Span)
 809                   -> Pattern<'tcx> {
 810         let ty = self.tables.node_type(id);
 811         let res = self.tables.qpath_res(qpath, id);
 812         let is_associated_const = match res {
 813             Res::Def(DefKind::AssociatedConst, _) => true,
 814             _ => false,
 815         };
 816         let kind = match res {
 817             Res::Def(DefKind::Const, def_id) | Res::Def(DefKind::AssociatedConst, def_id) => {
 818                 let substs = self.tables.node_substs(id);
 819                 match ty::Instance::resolve(
 820                     self.tcx,
 821                     self.param_env,
 822                     def_id,
 823                     substs,
 824                 ) {
 825                     Some(instance) => {
 826                         let cid = GlobalId {
 827                             instance,
 828                             promoted: None,
 829                         };
 830                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 831                             Ok(value) => {
 832                                 let pattern = self.const_to_pat(instance, value, id, span);
 833                                 if !is_associated_const {
 834                                     return pattern;
 835                                 }
 836
 837                                 let user_provided_types = self.tables().user_provided_types();
 838                                 return if let Some(u_ty) = user_provided_types.get(id) {
 839                                     let user_ty = PatternTypeProjection::from_user_type(*u_ty);
 840                                     Pattern {
 841                                         span,
 842                                         kind: Box::new(
 843                                             PatternKind::AscribeUserType {
 844                                                 subpattern: pattern,
 845                                                 ascription: Ascription {
 846                                                     /// Note that use `Contravariant` here. See the
 847                                                     /// `variance` field documentation for details.
 848                                                     variance: ty::Variance::Contravariant,
 849                                                     user_ty,
 850                                                     user_ty_span: span,
 851                                                 },
 852                                             }
 853                                         ),
 854                                         ty: value.ty,
 855                                     }
 856                                 } else {
 857                                     pattern
 858                                 }
 859                             },
 860                             Err(_) => {
 861                                 self.tcx.sess.span_err(
 862                                     span,
 863                                     "could not evaluate constant pattern",
 864                                 );
 865                                 PatternKind::Wild
 866                             }
 867                         }
 868                     },
 869                     None => {
 870                         self.errors.push(if is_associated_const {
 871                             PatternError::AssociatedConstInPattern(span)
 872                         } else {
 873                             PatternError::StaticInPattern(span)
 874                         });
 875                         PatternKind::Wild
 876                     },
 877                 }
 878             }
 879             _ => self.lower_variant_or_leaf(res, id, span, ty, vec![]),
 880         };
 881
 882         Pattern {
 883             span,
 884             ty,
 885             kind: Box::new(kind),
 886         }
 887     }
 888
 889     /// Converts literals, paths and negation of literals to patterns.
 890     /// The special case for negation exists to allow things like `-128_i8`
 891     /// which would overflow if we tried to evaluate `128_i8` and then negate
 892     /// afterwards.
 893     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 894         match expr.node {
 895             hir::ExprKind::Lit(ref lit) => {
 896                 let ty = self.tables.expr_ty(expr);
 897                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 898                     Ok(val) => {
 899                         let instance = ty::Instance::new(
 900                             self.tables.local_id_root.expect("literal outside any scope"),
 901                             self.substs,
 902                         );
 903                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 904                     },
 905                     Err(LitToConstError::UnparseableFloat) => {
 906                         self.errors.push(PatternError::FloatBug);
 907                         PatternKind::Wild
 908                     },
 909                     Err(LitToConstError::Reported) => PatternKind::Wild,
 910                 }
 911             },
 912             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 913             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 914                 let ty = self.tables.expr_ty(expr);
 915                 let lit = match expr.node {
 916                     hir::ExprKind::Lit(ref lit) => lit,
 917                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 918                 };
 919                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 920                     Ok(val) => {
 921                         let instance = ty::Instance::new(
 922                             self.tables.local_id_root.expect("literal outside any scope"),
 923                             self.substs,
 924                         );
 925                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 926                     },
 927                     Err(LitToConstError::UnparseableFloat) => {
 928                         self.errors.push(PatternError::FloatBug);
 929                         PatternKind::Wild
 930                     },
 931                     Err(LitToConstError::Reported) => PatternKind::Wild,
 932                 }
 933             }
 934             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 935         }
 936     }
 937
 938     /// Converts an evaluated constant to a pattern (if possible).
 939     /// This means aggregate values (like structs and enums) are converted
 940     /// to a pattern that matches the value (as if you'd compared via equality).
 941     fn const_to_pat(
 942         &self,
 943         instance: ty::Instance<'tcx>,
 944         cv: ty::Const<'tcx>,
 945         id: hir::HirId,
 946         span: Span,
 947     ) -> Pattern<'tcx> {
 948         debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
 949         let adt_subpattern = |i, variant_opt| {
 950             let field = Field::new(i);
 951             let val = const_field(self.tcx, self.param_env, variant_opt, field, cv);
 952             self.const_to_pat(instance, val, id, span)
 953         };
 954         let adt_subpatterns = |n, variant_opt| {
 955             (0..n).map(|i| {
 956                 let field = Field::new(i);
 957                 FieldPattern {
 958                     field,
 959                     pattern: adt_subpattern(i, variant_opt),
 960                 }
 961             }).collect::<Vec<_>>()
 962         };
 963         debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
 964         let kind = match cv.ty.sty {
 965             ty::Float(_) => {
 966                 self.tcx.lint_hir(
 967                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 968                     id,
 969                     span,
 970                     "floating-point types cannot be used in patterns",
 971                 );
 972                 PatternKind::Constant {
 973                     value: cv,
 974                 }
 975             }
 976             ty::Adt(adt_def, _) if adt_def.is_union() => {
 977                 // Matching on union fields is unsafe, we can't hide it in constants
 978                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 979                 PatternKind::Wild
 980             }
 981             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 982                 let path = self.tcx.def_path_str(adt_def.did);
 983                 let msg = format!(
 984                     "to use a constant of type `{}` in a pattern, \
 985                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 986                     path,
 987                     path,
 988                 );
 989                 self.tcx.sess.span_err(span, &msg);
 990                 PatternKind::Wild
 991             }
 992             ty::Ref(_, ty::TyS { sty: ty::Adt(adt_def, _), .. }, _)
 993             if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 994                 // HACK(estebank): Side-step ICE #53708, but anything other than erroring here
 995                 // would be wrong. Returnging `PatternKind::Wild` is not technically correct.
 996                 let path = self.tcx.def_path_str(adt_def.did);
 997                 let msg = format!(
 998                     "to use a constant of type `{}` in a pattern, \
 999                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
1000                     path,
1001                     path,
1002                 );
1003                 self.tcx.sess.span_err(span, &msg);
1004                 PatternKind::Wild
1005             }
1006             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
1007                 let variant_index = const_variant_index(self.tcx, self.param_env, cv);
1008                 let subpatterns = adt_subpatterns(
1009                     adt_def.variants[variant_index].fields.len(),
1010                     Some(variant_index),
1011                 );
1012                 PatternKind::Variant {
1013                     adt_def,
1014                     substs,
1015                     variant_index,
1016                     subpatterns,
1017                 }
1018             }
1019             ty::Adt(adt_def, _) => {
1020                 let struct_var = adt_def.non_enum_variant();
1021                 PatternKind::Leaf {
1022                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
1023                 }
1024             }
1025             ty::Tuple(fields) => {
1026                 PatternKind::Leaf {
1027                     subpatterns: adt_subpatterns(fields.len(), None),
1028                 }
1029             }
1030             ty::Array(_, n) => {
1031                 PatternKind::Array {
1032                     prefix: (0..n.unwrap_usize(self.tcx))
1033                         .map(|i| adt_subpattern(i as usize, None))
1034                         .collect(),
1035                     slice: None,
1036                     suffix: Vec::new(),
1037                 }
1038             }
1039             _ => {
1040                 PatternKind::Constant {
1041                     value: cv,
1042                 }
1043             }
1044         };
1045
1046         Pattern {
1047             span,
1048             ty: cv.ty,
1049             kind: Box::new(kind),
1050         }
1051     }
1052 }
1053
1054 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
1055     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
1056         self.tcx
1057     }
1058
1059     fn tables(&self) -> &ty::TypeckTables<'tcx> {
1060         self.tables
1061     }
1062 }
1063
1064
1065 pub trait PatternFoldable<'tcx> : Sized {
1066     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1067         self.super_fold_with(folder)
1068     }
1069
1070     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
1071 }
1072
1073 pub trait PatternFolder<'tcx> : Sized {
1074     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
1075         pattern.super_fold_with(self)
1076     }
1077
1078     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
1079         kind.super_fold_with(self)
1080     }
1081 }
1082
1083
1084 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
1085     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1086         let content: T = (**self).fold_with(folder);
1087         box content
1088     }
1089 }
1090
1091 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1092     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1093         self.iter().map(|t| t.fold_with(folder)).collect()
1094     }
1095 }
1096
1097 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1098     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1099         self.as_ref().map(|t| t.fold_with(folder))
1100     }
1101 }
1102
1103 macro_rules! CloneImpls {
1104     (<$lt_tcx:tt> $($ty:ty),+) => {
1105         $(
1106             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1107                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1108                     Clone::clone(self)
1109                 }
1110             }
1111         )+
1112     }
1113 }
1114
1115 CloneImpls!{ <'tcx>
1116     Span, Field, Mutability, ast::Name, hir::HirId, usize, ty::Const<'tcx>,
1117     Region<'tcx>, Ty<'tcx>, BindingMode, &'tcx AdtDef,
1118     SubstsRef<'tcx>, &'tcx Kind<'tcx>, UserType<'tcx>,
1119     UserTypeProjection, PatternTypeProjection<'tcx>
1120 }
1121
1122 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1123     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1124         FieldPattern {
1125             field: self.field.fold_with(folder),
1126             pattern: self.pattern.fold_with(folder)
1127         }
1128     }
1129 }
1130
1131 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1132     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1133         folder.fold_pattern(self)
1134     }
1135
1136     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1137         Pattern {
1138             ty: self.ty.fold_with(folder),
1139             span: self.span.fold_with(folder),
1140             kind: self.kind.fold_with(folder)
1141         }
1142     }
1143 }
1144
1145 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1146     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1147         folder.fold_pattern_kind(self)
1148     }
1149
1150     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1151         match *self {
1152             PatternKind::Wild => PatternKind::Wild,
1153             PatternKind::AscribeUserType {
1154                 ref subpattern,
1155                 ascription: Ascription {
1156                     variance,
1157                     ref user_ty,
1158                     user_ty_span,
1159                 },
1160             } => PatternKind::AscribeUserType {
1161                 subpattern: subpattern.fold_with(folder),
1162                 ascription: Ascription {
1163                     user_ty: user_ty.fold_with(folder),
1164                     variance,
1165                     user_ty_span,
1166                 },
1167             },
1168             PatternKind::Binding {
1169                 mutability,
1170                 name,
1171                 mode,
1172                 var,
1173                 ty,
1174                 ref subpattern,
1175             } => PatternKind::Binding {
1176                 mutability: mutability.fold_with(folder),
1177                 name: name.fold_with(folder),
1178                 mode: mode.fold_with(folder),
1179                 var: var.fold_with(folder),
1180                 ty: ty.fold_with(folder),
1181                 subpattern: subpattern.fold_with(folder),
1182             },
1183             PatternKind::Variant {
1184                 adt_def,
1185                 substs,
1186                 variant_index,
1187                 ref subpatterns,
1188             } => PatternKind::Variant {
1189                 adt_def: adt_def.fold_with(folder),
1190                 substs: substs.fold_with(folder),
1191                 variant_index,
1192                 subpatterns: subpatterns.fold_with(folder)
1193             },
1194             PatternKind::Leaf {
1195                 ref subpatterns,
1196             } => PatternKind::Leaf {
1197                 subpatterns: subpatterns.fold_with(folder),
1198             },
1199             PatternKind::Deref {
1200                 ref subpattern,
1201             } => PatternKind::Deref {
1202                 subpattern: subpattern.fold_with(folder),
1203             },
1204             PatternKind::Constant {
1205                 value
1206             } => PatternKind::Constant {
1207                 value: value.fold_with(folder)
1208             },
1209             PatternKind::Range(PatternRange {
1210                 lo,
1211                 hi,
1212                 ty,
1213                 end,
1214             }) => PatternKind::Range(PatternRange {
1215                 lo: lo.fold_with(folder),
1216                 hi: hi.fold_with(folder),
1217                 ty: ty.fold_with(folder),
1218                 end,
1219             }),
1220             PatternKind::Slice {
1221                 ref prefix,
1222                 ref slice,
1223                 ref suffix,
1224             } => PatternKind::Slice {
1225                 prefix: prefix.fold_with(folder),
1226                 slice: slice.fold_with(folder),
1227                 suffix: suffix.fold_with(folder)
1228             },
1229             PatternKind::Array {
1230                 ref prefix,
1231                 ref slice,
1232                 ref suffix
1233             } => PatternKind::Array {
1234                 prefix: prefix.fold_with(folder),
1235                 slice: slice.fold_with(folder),
1236                 suffix: suffix.fold_with(folder)
1237             },
1238         }
1239     }
1240 }
1241
1242 pub fn compare_const_vals<'a, 'gcx, 'tcx>(
1243     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1244     a: ty::Const<'tcx>,
1245     b: ty::Const<'tcx>,
1246     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1247 ) -> Option<Ordering> {
1248     trace!("compare_const_vals: {:?}, {:?}", a, b);
1249
1250     let from_bool = |v: bool| {
1251         if v {
1252             Some(Ordering::Equal)
1253         } else {
1254             None
1255         }
1256     };
1257
1258     let fallback = || from_bool(a == b);
1259
1260     // Use the fallback if any type differs
1261     if a.ty != b.ty || a.ty != ty.value {
1262         return fallback();
1263     }
1264
1265     // FIXME: This should use assert_bits(ty) instead of use_bits
1266     // but triggers possibly bugs due to mismatching of arrays and slices
1267     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1268         use ::rustc_apfloat::Float;
1269         return match ty.value.sty {
1270             ty::Float(ast::FloatTy::F32) => {
1271                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1272                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1273                 l.partial_cmp(&r)
1274             }
1275             ty::Float(ast::FloatTy::F64) => {
1276                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1277                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1278                 l.partial_cmp(&r)
1279             }
1280             ty::Int(ity) => {
1281                 use rustc::ty::layout::{Integer, IntegerExt};
1282                 use syntax::attr::SignedInt;
1283                 let size = Integer::from_attr(&tcx, SignedInt(ity)).size();
1284                 let a = sign_extend(a, size);
1285                 let b = sign_extend(b, size);
1286                 Some((a as i128).cmp(&(b as i128)))
1287             }
1288             _ => Some(a.cmp(&b)),
1289         }
1290     }
1291
1292     if let ty::Str = ty.value.sty {
1293         match (a.val, b.val) {
1294             (
1295                 ConstValue::Slice(
1296                     Scalar::Ptr(ptr_a),
1297                     len_a,
1298                 ),
1299                 ConstValue::Slice(
1300                     Scalar::Ptr(ptr_b),
1301                     len_b,
1302                 ),
1303             ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1304                 if len_a == len_b {
1305                     let map = tcx.alloc_map.lock();
1306                     let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1307                     let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1308                     if alloc_a.bytes.len() as u64 == len_a {
1309                         return from_bool(alloc_a == alloc_b);
1310                     }
1311                 }
1312             }
1313             _ => (),
1314         }
1315     }
1316
1317     fallback()
1318 }