src/librustc_mir/hair/pattern/mod.rs

   1 //! Code to validate patterns/matches
   2
   3 mod _match;
   4 mod check_match;
   5
   6 pub use self::check_match::check_crate;
   7 pub(crate) use self::check_match::check_match;
   8
   9 use const_eval::{const_field, const_variant_index};
  10
  11 use hair::util::UserAnnotatedTyHelpers;
  12 use hair::constant::*;
  13
  14 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability};
  15 use rustc::mir::{ProjectionElem, UserTypeProjection, UserTypeProjections};
  16 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  17 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, Lift};
  18 use rustc::ty::{CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, UserTypeAnnotation};
  19 use rustc::ty::subst::{Substs, Kind};
  20 use rustc::ty::layout::VariantIdx;
  21 use rustc::hir::{self, PatKind, RangeEnd};
  22 use rustc::hir::def::{Def, CtorKind};
  23 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  24
  25 use rustc_data_structures::indexed_vec::Idx;
  26
  27 use std::cmp::Ordering;
  28 use std::fmt;
  29 use syntax::ast;
  30 use syntax::ptr::P;
  31 use syntax_pos::Span;
  32
  33 #[derive(Clone, Debug)]
  34 pub enum PatternError {
  35     AssociatedConstInPattern(Span),
  36     StaticInPattern(Span),
  37     FloatBug,
  38     NonConstPath(Span),
  39 }
  40
  41 #[derive(Copy, Clone, Debug)]
  42 pub enum BindingMode<'tcx> {
  43     ByValue,
  44     ByRef(Region<'tcx>, BorrowKind),
  45 }
  46
  47 #[derive(Clone, Debug)]
  48 pub struct FieldPattern<'tcx> {
  49     pub field: Field,
  50     pub pattern: Pattern<'tcx>,
  51 }
  52
  53 #[derive(Clone, Debug)]
  54 pub struct Pattern<'tcx> {
  55     pub ty: Ty<'tcx>,
  56     pub span: Span,
  57     pub kind: Box<PatternKind<'tcx>>,
  58 }
  59
  60
  61 #[derive(Clone, Debug)]
  62 pub(crate) struct PatternTypeProjections<'tcx> {
  63     contents: Vec<(PatternTypeProjection<'tcx>, Span)>,
  64 }
  65
  66 impl<'tcx> PatternTypeProjections<'tcx> {
  67     pub(crate) fn user_ty(
  68         self,
  69         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
  70     ) -> UserTypeProjections<'tcx> {
  71         UserTypeProjections::from_projections(
  72             self.contents
  73                 .into_iter()
  74                 .map(|(pat_ty_proj, span)| (pat_ty_proj.user_ty(annotations, span), span))
  75         )
  76     }
  77
  78     pub(crate) fn none() -> Self {
  79         PatternTypeProjections { contents: vec![] }
  80     }
  81
  82     pub(crate) fn ref_binding(&self) -> Self {
  83         // FIXME(#55401): ignore for now
  84         PatternTypeProjections { contents: vec![] }
  85     }
  86
  87     fn map_projs(&self,
  88                  mut f: impl FnMut(&PatternTypeProjection<'tcx>) -> PatternTypeProjection<'tcx>)
  89                  -> Self
  90     {
  91         PatternTypeProjections {
  92             contents: self.contents
  93                 .iter()
  94                 .map(|(proj, span)| (f(proj), *span))
  95                 .collect(), }
  96     }
  97
  98     pub(crate) fn index(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.index()) }
  99
 100     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
 101         self.map_projs(|pat_ty_proj| pat_ty_proj.subslice(from, to))
 102     }
 103
 104     pub(crate) fn deref(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.deref()) }
 105
 106     pub(crate) fn leaf(&self, field: Field) -> Self {
 107         self.map_projs(|pat_ty_proj| pat_ty_proj.leaf(field))
 108     }
 109
 110     pub(crate) fn variant(&self,
 111                           adt_def: &'tcx AdtDef,
 112                           variant_index: VariantIdx,
 113                           field: Field) -> Self {
 114         self.map_projs(|pat_ty_proj| pat_ty_proj.variant(adt_def, variant_index, field))
 115     }
 116
 117     pub(crate) fn add_user_type(&self, user_ty: &PatternTypeProjection<'tcx>, sp: Span) -> Self {
 118         let mut new = self.clone();
 119         new.contents.push((user_ty.clone(), sp));
 120         new
 121     }
 122 }
 123
 124 #[derive(Clone, Debug)]
 125 pub struct PatternTypeProjection<'tcx> {
 126     pub base: CanonicalUserTypeAnnotation<'tcx>,
 127     pub projs: Vec<ProjectionElem<'tcx, (), ()>>,
 128 }
 129
 130 impl<'tcx> PatternTypeProjection<'tcx> {
 131     pub(crate) fn index(&self) -> Self {
 132         let mut new = self.clone();
 133         new.projs.push(ProjectionElem::Index(()));
 134         new
 135     }
 136
 137     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
 138         let mut new = self.clone();
 139         new.projs.push(ProjectionElem::Subslice { from, to });
 140         new
 141     }
 142
 143     pub(crate) fn deref(&self) -> Self {
 144         let mut new = self.clone();
 145         new.projs.push(ProjectionElem::Deref);
 146         new
 147     }
 148
 149     pub(crate) fn leaf(&self, field: Field) -> Self {
 150         let mut new = self.clone();
 151         new.projs.push(ProjectionElem::Field(field, ()));
 152         new
 153     }
 154
 155     pub(crate) fn variant(&self,
 156                           adt_def: &'tcx AdtDef,
 157                           variant_index: VariantIdx,
 158                           field: Field) -> Self {
 159         let mut new = self.clone();
 160         new.projs.push(ProjectionElem::Downcast(adt_def, variant_index));
 161         new.projs.push(ProjectionElem::Field(field, ()));
 162         new
 163     }
 164
 165     pub(crate) fn from_user_type(user_annotation: CanonicalUserTypeAnnotation<'tcx>) -> Self {
 166         Self {
 167             base: user_annotation,
 168             projs: Vec::new(),
 169         }
 170     }
 171
 172     pub(crate) fn user_ty(
 173         self,
 174         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
 175         span: Span,
 176     ) -> UserTypeProjection<'tcx> {
 177         let annotation_index = annotations.push((span, self.base));
 178         UserTypeProjection {
 179             base: annotation_index,
 180             projs: self.projs
 181         }
 182     }
 183 }
 184
 185 #[derive(Clone, Debug)]
 186 pub enum PatternKind<'tcx> {
 187     Wild,
 188
 189     AscribeUserType {
 190         user_ty: PatternTypeProjection<'tcx>,
 191         subpattern: Pattern<'tcx>,
 192         user_ty_span: Span,
 193     },
 194
 195     /// x, ref x, x @ P, etc
 196     Binding {
 197         mutability: Mutability,
 198         name: ast::Name,
 199         mode: BindingMode<'tcx>,
 200         var: ast::NodeId,
 201         ty: Ty<'tcx>,
 202         subpattern: Option<Pattern<'tcx>>,
 203     },
 204
 205     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
 206     Variant {
 207         adt_def: &'tcx AdtDef,
 208         substs: &'tcx Substs<'tcx>,
 209         variant_index: VariantIdx,
 210         subpatterns: Vec<FieldPattern<'tcx>>,
 211     },
 212
 213     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
 214     Leaf {
 215         subpatterns: Vec<FieldPattern<'tcx>>,
 216     },
 217
 218     /// box P, &P, &mut P, etc
 219     Deref {
 220         subpattern: Pattern<'tcx>,
 221     },
 222
 223     Constant {
 224         value: &'tcx ty::Const<'tcx>,
 225     },
 226
 227     Range(PatternRange<'tcx>),
 228
 229     /// matches against a slice, checking the length and extracting elements.
 230     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 231     /// e.g., `&[ref xs..]`.
 232     Slice {
 233         prefix: Vec<Pattern<'tcx>>,
 234         slice: Option<Pattern<'tcx>>,
 235         suffix: Vec<Pattern<'tcx>>,
 236     },
 237
 238     /// fixed match against an array, irrefutable
 239     Array {
 240         prefix: Vec<Pattern<'tcx>>,
 241         slice: Option<Pattern<'tcx>>,
 242         suffix: Vec<Pattern<'tcx>>,
 243     },
 244 }
 245
 246 #[derive(Clone, Copy, Debug, PartialEq)]
 247 pub struct PatternRange<'tcx> {
 248     pub lo: &'tcx ty::Const<'tcx>,
 249     pub hi: &'tcx ty::Const<'tcx>,
 250     pub ty: Ty<'tcx>,
 251     pub end: RangeEnd,
 252 }
 253
 254 impl<'tcx> fmt::Display for Pattern<'tcx> {
 255     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 256         match *self.kind {
 257             PatternKind::Wild => write!(f, "_"),
 258             PatternKind::AscribeUserType { ref subpattern, .. } =>
 259                 write!(f, "{}: _", subpattern),
 260             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 261                 let is_mut = match mode {
 262                     BindingMode::ByValue => mutability == Mutability::Mut,
 263                     BindingMode::ByRef(_, bk) => {
 264                         write!(f, "ref ")?;
 265                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 266                     }
 267                 };
 268                 if is_mut {
 269                     write!(f, "mut ")?;
 270                 }
 271                 write!(f, "{}", name)?;
 272                 if let Some(ref subpattern) = *subpattern {
 273                     write!(f, " @ {}", subpattern)?;
 274                 }
 275                 Ok(())
 276             }
 277             PatternKind::Variant { ref subpatterns, .. } |
 278             PatternKind::Leaf { ref subpatterns } => {
 279                 let variant = match *self.kind {
 280                     PatternKind::Variant { adt_def, variant_index, .. } => {
 281                         Some(&adt_def.variants[variant_index])
 282                     }
 283                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 284                         if !adt.is_enum() {
 285                             Some(&adt.variants[VariantIdx::new(0)])
 286                         } else {
 287                             None
 288                         }
 289                     } else {
 290                         None
 291                     }
 292                 };
 293
 294                 let mut first = true;
 295                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 296
 297                 if let Some(variant) = variant {
 298                     write!(f, "{}", variant.ident)?;
 299
 300                     // Only for Adt we can have `S {...}`,
 301                     // which we handle separately here.
 302                     if variant.ctor_kind == CtorKind::Fictive {
 303                         write!(f, " {{ ")?;
 304
 305                         let mut printed = 0;
 306                         for p in subpatterns {
 307                             if let PatternKind::Wild = *p.pattern.kind {
 308                                 continue;
 309                             }
 310                             let name = variant.fields[p.field.index()].ident;
 311                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 312                             printed += 1;
 313                         }
 314
 315                         if printed < variant.fields.len() {
 316                             write!(f, "{}..", start_or_continue())?;
 317                         }
 318
 319                         return write!(f, " }}");
 320                     }
 321                 }
 322
 323                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 324                 if num_fields != 0 || variant.is_none() {
 325                     write!(f, "(")?;
 326                     for i in 0..num_fields {
 327                         write!(f, "{}", start_or_continue())?;
 328
 329                         // Common case: the field is where we expect it.
 330                         if let Some(p) = subpatterns.get(i) {
 331                             if p.field.index() == i {
 332                                 write!(f, "{}", p.pattern)?;
 333                                 continue;
 334                             }
 335                         }
 336
 337                         // Otherwise, we have to go looking for it.
 338                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 339                             write!(f, "{}", p.pattern)?;
 340                         } else {
 341                             write!(f, "_")?;
 342                         }
 343                     }
 344                     write!(f, ")")?;
 345                 }
 346
 347                 Ok(())
 348             }
 349             PatternKind::Deref { ref subpattern } => {
 350                 match self.ty.sty {
 351                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 352                     ty::Ref(_, _, mutbl) => {
 353                         write!(f, "&")?;
 354                         if mutbl == hir::MutMutable {
 355                             write!(f, "mut ")?;
 356                         }
 357                     }
 358                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 359                 }
 360                 write!(f, "{}", subpattern)
 361             }
 362             PatternKind::Constant { value } => {
 363                 fmt_const_val(f, value)
 364             }
 365             PatternKind::Range(PatternRange { lo, hi, ty: _, end }) => {
 366                 fmt_const_val(f, lo)?;
 367                 match end {
 368                     RangeEnd::Included => write!(f, "..=")?,
 369                     RangeEnd::Excluded => write!(f, "..")?,
 370                 }
 371                 fmt_const_val(f, hi)
 372             }
 373             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 374             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 375                 let mut first = true;
 376                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 377                 write!(f, "[")?;
 378                 for p in prefix {
 379                     write!(f, "{}{}", start_or_continue(), p)?;
 380                 }
 381                 if let Some(ref slice) = *slice {
 382                     write!(f, "{}", start_or_continue())?;
 383                     match *slice.kind {
 384                         PatternKind::Wild => {}
 385                         _ => write!(f, "{}", slice)?
 386                     }
 387                     write!(f, "..")?;
 388                 }
 389                 for p in suffix {
 390                     write!(f, "{}{}", start_or_continue(), p)?;
 391                 }
 392                 write!(f, "]")
 393             }
 394         }
 395     }
 396 }
 397
 398 pub struct PatternContext<'a, 'tcx: 'a> {
 399     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 400     pub param_env: ty::ParamEnv<'tcx>,
 401     pub tables: &'a ty::TypeckTables<'tcx>,
 402     pub substs: &'tcx Substs<'tcx>,
 403     pub errors: Vec<PatternError>,
 404 }
 405
 406 impl<'a, 'tcx> Pattern<'tcx> {
 407     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 408                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 409                     tables: &'a ty::TypeckTables<'tcx>,
 410                     pat: &'tcx hir::Pat) -> Self {
 411         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 412         let result = pcx.lower_pattern(pat);
 413         if !pcx.errors.is_empty() {
 414             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 415             tcx.sess.delay_span_bug(pat.span, &msg);
 416         }
 417         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 418         result
 419     }
 420 }
 421
 422 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 423     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 424                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 425                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 426         PatternContext {
 427             tcx,
 428             param_env: param_env_and_substs.param_env,
 429             tables,
 430             substs: param_env_and_substs.value,
 431             errors: vec![]
 432         }
 433     }
 434
 435     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 436         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 437         // pattern has the type that results *after* dereferencing. For example, in this code:
 438         //
 439         // ```
 440         // match &&Some(0i32) {
 441         //     Some(n) => { ... },
 442         //     _ => { ... },
 443         // }
 444         // ```
 445         //
 446         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 447         // determined in rustc_typeck::check::match). The adjustments would be
 448         //
 449         // `vec![&&Option<i32>, &Option<i32>]`.
 450         //
 451         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 452         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 453         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 454         // gets the least-dereferenced type).
 455         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 456         self.tables
 457             .pat_adjustments()
 458             .get(pat.hir_id)
 459             .unwrap_or(&vec![])
 460             .iter()
 461             .rev()
 462             .fold(unadjusted_pat, |pat, ref_ty| {
 463                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 464                     Pattern {
 465                         span: pat.span,
 466                         ty: ref_ty,
 467                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 468                     }
 469                 },
 470             )
 471     }
 472
 473     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 474         let mut ty = self.tables.node_id_to_type(pat.hir_id);
 475
 476         let kind = match pat.node {
 477             PatKind::Wild => PatternKind::Wild,
 478
 479             PatKind::Lit(ref value) => self.lower_lit(value),
 480
 481             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 482                 match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
 483                     (PatternKind::Constant { value: lo },
 484                      PatternKind::Constant { value: hi }) => {
 485                         use std::cmp::Ordering;
 486                         let cmp = compare_const_vals(
 487                             self.tcx,
 488                             lo,
 489                             hi,
 490                             self.param_env.and(ty),
 491                         );
 492                         match (end, cmp) {
 493                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 494                                 PatternKind::Range(PatternRange { lo, hi, ty, end }),
 495                             (RangeEnd::Excluded, _) => {
 496                                 span_err!(
 497                                     self.tcx.sess,
 498                                     lo_expr.span,
 499                                     E0579,
 500                                     "lower range bound must be less than upper",
 501                                 );
 502                                 PatternKind::Wild
 503                             }
 504                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 505                                 PatternKind::Constant { value: lo }
 506                             }
 507                             (RangeEnd::Included, Some(Ordering::Less)) => {
 508                                 PatternKind::Range(PatternRange { lo, hi, ty, end })
 509                             }
 510                             (RangeEnd::Included, _) => {
 511                                 let mut err = struct_span_err!(
 512                                     self.tcx.sess,
 513                                     lo_expr.span,
 514                                     E0030,
 515                                     "lower range bound must be less than or equal to upper"
 516                                 );
 517                                 err.span_label(
 518                                     lo_expr.span,
 519                                     "lower bound larger than upper bound",
 520                                 );
 521                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 522                                     err.note("When matching against a range, the compiler \
 523                                               verifies that the range is non-empty. Range \
 524                                               patterns include both end-points, so this is \
 525                                               equivalent to requiring the start of the range \
 526                                               to be less than or equal to the end of the range.");
 527                                 }
 528                                 err.emit();
 529                                 PatternKind::Wild
 530                             }
 531                         }
 532                     }
 533                     _ => PatternKind::Wild
 534                 }
 535             }
 536
 537             PatKind::Path(ref qpath) => {
 538                 return self.lower_path(qpath, pat.hir_id, pat.span);
 539             }
 540
 541             PatKind::Ref(ref subpattern, _) |
 542             PatKind::Box(ref subpattern) => {
 543                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 544             }
 545
 546             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 547                 match ty.sty {
 548                     ty::Ref(_, ty, _) =>
 549                         PatternKind::Deref {
 550                             subpattern: Pattern {
 551                                 ty,
 552                                 span: pat.span,
 553                                 kind: Box::new(self.slice_or_array_pattern(
 554                                     pat.span, ty, prefix, slice, suffix))
 555                             },
 556                         },
 557                     ty::Slice(..) |
 558                     ty::Array(..) =>
 559                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 560                     ty::Error => { // Avoid ICE
 561                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 562                     }
 563                     ref sty =>
 564                         span_bug!(
 565                             pat.span,
 566                             "unexpanded type for vector pattern: {:?}",
 567                             sty),
 568                 }
 569             }
 570
 571             PatKind::Tuple(ref subpatterns, ddpos) => {
 572                 match ty.sty {
 573                     ty::Tuple(ref tys) => {
 574                         let subpatterns =
 575                             subpatterns.iter()
 576                                        .enumerate_and_adjust(tys.len(), ddpos)
 577                                        .map(|(i, subpattern)| FieldPattern {
 578                                             field: Field::new(i),
 579                                             pattern: self.lower_pattern(subpattern)
 580                                        })
 581                                        .collect();
 582
 583                         PatternKind::Leaf { subpatterns }
 584                     }
 585                     ty::Error => { // Avoid ICE (#50577)
 586                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 587                     }
 588                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 589                 }
 590             }
 591
 592             PatKind::Binding(_, id, ident, ref sub) => {
 593                 let var_ty = self.tables.node_id_to_type(pat.hir_id);
 594                 let region = match var_ty.sty {
 595                     ty::Ref(r, _, _) => Some(r),
 596                     ty::Error => { // Avoid ICE
 597                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 598                     }
 599                     _ => None,
 600                 };
 601                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 602                                                          .expect("missing binding mode");
 603                 let (mutability, mode) = match bm {
 604                     ty::BindByValue(hir::MutMutable) =>
 605                         (Mutability::Mut, BindingMode::ByValue),
 606                     ty::BindByValue(hir::MutImmutable) =>
 607                         (Mutability::Not, BindingMode::ByValue),
 608                     ty::BindByReference(hir::MutMutable) =>
 609                         (Mutability::Not, BindingMode::ByRef(
 610                             region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
 611                     ty::BindByReference(hir::MutImmutable) =>
 612                         (Mutability::Not, BindingMode::ByRef(
 613                             region.unwrap(), BorrowKind::Shared)),
 614                 };
 615
 616                 // A ref x pattern is the same node used for x, and as such it has
 617                 // x's type, which is &T, where we want T (the type being matched).
 618                 if let ty::BindByReference(_) = bm {
 619                     if let ty::Ref(_, rty, _) = ty.sty {
 620                         ty = rty;
 621                     } else {
 622                         bug!("`ref {}` has wrong type {}", ident, ty);
 623                     }
 624                 }
 625
 626                 PatternKind::Binding {
 627                     mutability,
 628                     mode,
 629                     name: ident.name,
 630                     var: id,
 631                     ty: var_ty,
 632                     subpattern: self.lower_opt_pattern(sub),
 633                 }
 634             }
 635
 636             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 637                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 638                 let adt_def = match ty.sty {
 639                     ty::Adt(adt_def, _) => adt_def,
 640                     ty::Error => { // Avoid ICE (#50585)
 641                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 642                     }
 643                     _ => span_bug!(pat.span,
 644                                    "tuple struct pattern not applied to an ADT {:?}",
 645                                    ty.sty),
 646                 };
 647                 let variant_def = adt_def.variant_of_def(def);
 648
 649                 let subpatterns =
 650                         subpatterns.iter()
 651                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 652                                    .map(|(i, field)| FieldPattern {
 653                                        field: Field::new(i),
 654                                        pattern: self.lower_pattern(field),
 655                                    })
 656                     .collect();
 657
 658                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 659             }
 660
 661             PatKind::Struct(ref qpath, ref fields, _) => {
 662                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 663                 let subpatterns =
 664                     fields.iter()
 665                           .map(|field| {
 666                               FieldPattern {
 667                                   field: Field::new(self.tcx.field_index(field.node.id,
 668                                                                          self.tables)),
 669                                   pattern: self.lower_pattern(&field.node.pat),
 670                               }
 671                           })
 672                           .collect();
 673
 674                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 675             }
 676         };
 677
 678         Pattern {
 679             span: pat.span,
 680             ty,
 681             kind: Box::new(kind),
 682         }
 683     }
 684
 685     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 686         pats.iter().map(|p| self.lower_pattern(p)).collect()
 687     }
 688
 689     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 690     {
 691         pat.as_ref().map(|p| self.lower_pattern(p))
 692     }
 693
 694     fn flatten_nested_slice_patterns(
 695         &mut self,
 696         prefix: Vec<Pattern<'tcx>>,
 697         slice: Option<Pattern<'tcx>>,
 698         suffix: Vec<Pattern<'tcx>>)
 699         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 700     {
 701         let orig_slice = match slice {
 702             Some(orig_slice) => orig_slice,
 703             None => return (prefix, slice, suffix)
 704         };
 705         let orig_prefix = prefix;
 706         let orig_suffix = suffix;
 707
 708         // dance because of intentional borrow-checker stupidity.
 709         let kind = *orig_slice.kind;
 710         match kind {
 711             PatternKind::Slice { prefix, slice, mut suffix } |
 712             PatternKind::Array { prefix, slice, mut suffix } => {
 713                 let mut orig_prefix = orig_prefix;
 714
 715                 orig_prefix.extend(prefix);
 716                 suffix.extend(orig_suffix);
 717
 718                 (orig_prefix, slice, suffix)
 719             }
 720             _ => {
 721                 (orig_prefix, Some(Pattern {
 722                     kind: box kind, ..orig_slice
 723                 }), orig_suffix)
 724             }
 725         }
 726     }
 727
 728     fn slice_or_array_pattern(
 729         &mut self,
 730         span: Span,
 731         ty: Ty<'tcx>,
 732         prefix: &'tcx [P<hir::Pat>],
 733         slice: &'tcx Option<P<hir::Pat>>,
 734         suffix: &'tcx [P<hir::Pat>])
 735         -> PatternKind<'tcx>
 736     {
 737         let prefix = self.lower_patterns(prefix);
 738         let slice = self.lower_opt_pattern(slice);
 739         let suffix = self.lower_patterns(suffix);
 740         let (prefix, slice, suffix) =
 741             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 742
 743         match ty.sty {
 744             ty::Slice(..) => {
 745                 // matching a slice or fixed-length array
 746                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 747             }
 748
 749             ty::Array(_, len) => {
 750                 // fixed-length array
 751                 let len = len.unwrap_usize(self.tcx);
 752                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 753                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 754             }
 755
 756             _ => {
 757                 span_bug!(span, "bad slice pattern type {:?}", ty);
 758             }
 759         }
 760     }
 761
 762     fn lower_variant_or_leaf(
 763         &mut self,
 764         def: Def,
 765         hir_id: hir::HirId,
 766         span: Span,
 767         ty: Ty<'tcx>,
 768         subpatterns: Vec<FieldPattern<'tcx>>,
 769     ) -> PatternKind<'tcx> {
 770         let mut kind = match def {
 771             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 772                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 773                 let adt_def = self.tcx.adt_def(enum_id);
 774                 if adt_def.is_enum() {
 775                     let substs = match ty.sty {
 776                         ty::Adt(_, substs) |
 777                         ty::FnDef(_, substs) => substs,
 778                         ty::Error => {  // Avoid ICE (#50585)
 779                             return PatternKind::Wild;
 780                         }
 781                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 782                     };
 783                     PatternKind::Variant {
 784                         adt_def,
 785                         substs,
 786                         variant_index: adt_def.variant_index_with_id(variant_id),
 787                         subpatterns,
 788                     }
 789                 } else {
 790                     PatternKind::Leaf { subpatterns }
 791                 }
 792             }
 793
 794             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 795             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) => {
 796                 PatternKind::Leaf { subpatterns }
 797             }
 798
 799             _ => {
 800                 self.errors.push(PatternError::NonConstPath(span));
 801                 PatternKind::Wild
 802             }
 803         };
 804
 805         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 806             debug!("lower_variant_or_leaf: user_ty={:?} span={:?}", user_ty, span);
 807             kind = PatternKind::AscribeUserType {
 808                 subpattern: Pattern {
 809                     span,
 810                     ty,
 811                     kind: Box::new(kind),
 812                 },
 813                 user_ty: PatternTypeProjection::from_user_type(user_ty),
 814                 user_ty_span: span,
 815             };
 816         }
 817
 818         kind
 819     }
 820
 821     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 822     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 823     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 824     fn lower_path(&mut self,
 825                   qpath: &hir::QPath,
 826                   id: hir::HirId,
 827                   span: Span)
 828                   -> Pattern<'tcx> {
 829         let ty = self.tables.node_id_to_type(id);
 830         let def = self.tables.qpath_def(qpath, id);
 831         let is_associated_const = match def {
 832             Def::AssociatedConst(_) => true,
 833             _ => false,
 834         };
 835         let kind = match def {
 836             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 837                 let substs = self.tables.node_substs(id);
 838                 match ty::Instance::resolve(
 839                     self.tcx,
 840                     self.param_env,
 841                     def_id,
 842                     substs,
 843                 ) {
 844                     Some(instance) => {
 845                         let cid = GlobalId {
 846                             instance,
 847                             promoted: None,
 848                         };
 849                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 850                             Ok(value) => {
 851                                 let pattern = self.const_to_pat(instance, value, id, span);
 852                                 if !is_associated_const {
 853                                     return pattern;
 854                                 }
 855
 856                                 let user_provided_types = self.tables().user_provided_types();
 857                                 return if let Some(u_ty) = user_provided_types.get(id) {
 858                                     let user_ty = PatternTypeProjection::from_user_type(*u_ty);
 859                                     Pattern {
 860                                         span,
 861                                         kind: Box::new(
 862                                             PatternKind::AscribeUserType {
 863                                                 subpattern: pattern,
 864                                                 user_ty,
 865                                                 user_ty_span: span,
 866                                             }
 867                                         ),
 868                                         ty: value.ty,
 869                                     }
 870                                 } else {
 871                                     pattern
 872                                 }
 873                             },
 874                             Err(_) => {
 875                                 self.tcx.sess.span_err(
 876                                     span,
 877                                     "could not evaluate constant pattern",
 878                                 );
 879                                 PatternKind::Wild
 880                             }
 881                         }
 882                     },
 883                     None => {
 884                         self.errors.push(if is_associated_const {
 885                             PatternError::AssociatedConstInPattern(span)
 886                         } else {
 887                             PatternError::StaticInPattern(span)
 888                         });
 889                         PatternKind::Wild
 890                     },
 891                 }
 892             }
 893             _ => self.lower_variant_or_leaf(def, id, span, ty, vec![]),
 894         };
 895
 896         Pattern {
 897             span,
 898             ty,
 899             kind: Box::new(kind),
 900         }
 901     }
 902
 903     /// Converts literals, paths and negation of literals to patterns.
 904     /// The special case for negation exists to allow things like -128i8
 905     /// which would overflow if we tried to evaluate 128i8 and then negate
 906     /// afterwards.
 907     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 908         match expr.node {
 909             hir::ExprKind::Lit(ref lit) => {
 910                 let ty = self.tables.expr_ty(expr);
 911                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 912                     Ok(val) => {
 913                         let instance = ty::Instance::new(
 914                             self.tables.local_id_root.expect("literal outside any scope"),
 915                             self.substs,
 916                         );
 917                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 918                     },
 919                     Err(LitToConstError::UnparseableFloat) => {
 920                         self.errors.push(PatternError::FloatBug);
 921                         PatternKind::Wild
 922                     },
 923                     Err(LitToConstError::Reported) => PatternKind::Wild,
 924                 }
 925             },
 926             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 927             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 928                 let ty = self.tables.expr_ty(expr);
 929                 let lit = match expr.node {
 930                     hir::ExprKind::Lit(ref lit) => lit,
 931                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 932                 };
 933                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 934                     Ok(val) => {
 935                         let instance = ty::Instance::new(
 936                             self.tables.local_id_root.expect("literal outside any scope"),
 937                             self.substs,
 938                         );
 939                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 940                     },
 941                     Err(LitToConstError::UnparseableFloat) => {
 942                         self.errors.push(PatternError::FloatBug);
 943                         PatternKind::Wild
 944                     },
 945                     Err(LitToConstError::Reported) => PatternKind::Wild,
 946                 }
 947             }
 948             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 949         }
 950     }
 951
 952     /// Converts an evaluated constant to a pattern (if possible).
 953     /// This means aggregate values (like structs and enums) are converted
 954     /// to a pattern that matches the value (as if you'd compare via eq).
 955     fn const_to_pat(
 956         &self,
 957         instance: ty::Instance<'tcx>,
 958         cv: &'tcx ty::Const<'tcx>,
 959         id: hir::HirId,
 960         span: Span,
 961     ) -> Pattern<'tcx> {
 962         debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
 963         let adt_subpattern = |i, variant_opt| {
 964             let field = Field::new(i);
 965             let val = const_field(
 966                 self.tcx, self.param_env, instance,
 967                 variant_opt, field, cv,
 968             ).expect("field access failed");
 969             self.const_to_pat(instance, val, id, span)
 970         };
 971         let adt_subpatterns = |n, variant_opt| {
 972             (0..n).map(|i| {
 973                 let field = Field::new(i);
 974                 FieldPattern {
 975                     field,
 976                     pattern: adt_subpattern(i, variant_opt),
 977                 }
 978             }).collect::<Vec<_>>()
 979         };
 980         debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
 981         let kind = match cv.ty.sty {
 982             ty::Float(_) => {
 983                 let id = self.tcx.hir().hir_to_node_id(id);
 984                 self.tcx.lint_node(
 985                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 986                     id,
 987                     span,
 988                     "floating-point types cannot be used in patterns",
 989                 );
 990                 PatternKind::Constant {
 991                     value: cv,
 992                 }
 993             },
 994             ty::Adt(adt_def, _) if adt_def.is_union() => {
 995                 // Matching on union fields is unsafe, we can't hide it in constants
 996                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 997                 PatternKind::Wild
 998             }
 999             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
1000                 let msg = format!("to use a constant of type `{}` in a pattern, \
1001                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
1002                                     self.tcx.item_path_str(adt_def.did),
1003                                     self.tcx.item_path_str(adt_def.did));
1004                 self.tcx.sess.span_err(span, &msg);
1005                 PatternKind::Wild
1006             },
1007             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
1008                 let variant_index = const_variant_index(
1009                     self.tcx, self.param_env, instance, cv
1010                 ).expect("const_variant_index failed");
1011                 let subpatterns = adt_subpatterns(
1012                     adt_def.variants[variant_index].fields.len(),
1013                     Some(variant_index),
1014                 );
1015                 PatternKind::Variant {
1016                     adt_def,
1017                     substs,
1018                     variant_index,
1019                     subpatterns,
1020                 }
1021             },
1022             ty::Adt(adt_def, _) => {
1023                 let struct_var = adt_def.non_enum_variant();
1024                 PatternKind::Leaf {
1025                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
1026                 }
1027             }
1028             ty::Tuple(fields) => {
1029                 PatternKind::Leaf {
1030                     subpatterns: adt_subpatterns(fields.len(), None),
1031                 }
1032             }
1033             ty::Array(_, n) => {
1034                 PatternKind::Array {
1035                     prefix: (0..n.unwrap_usize(self.tcx))
1036                         .map(|i| adt_subpattern(i as usize, None))
1037                         .collect(),
1038                     slice: None,
1039                     suffix: Vec::new(),
1040                 }
1041             }
1042             _ => {
1043                 PatternKind::Constant {
1044                     value: cv,
1045                 }
1046             },
1047         };
1048
1049         Pattern {
1050             span,
1051             ty: cv.ty,
1052             kind: Box::new(kind),
1053         }
1054     }
1055 }
1056
1057 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
1058     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
1059         self.tcx
1060     }
1061
1062     fn tables(&self) -> &ty::TypeckTables<'tcx> {
1063         self.tables
1064     }
1065 }
1066
1067
1068 pub trait PatternFoldable<'tcx> : Sized {
1069     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1070         self.super_fold_with(folder)
1071     }
1072
1073     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
1074 }
1075
1076 pub trait PatternFolder<'tcx> : Sized {
1077     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
1078         pattern.super_fold_with(self)
1079     }
1080
1081     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
1082         kind.super_fold_with(self)
1083     }
1084 }
1085
1086
1087 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
1088     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1089         let content: T = (**self).fold_with(folder);
1090         box content
1091     }
1092 }
1093
1094 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1095     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1096         self.iter().map(|t| t.fold_with(folder)).collect()
1097     }
1098 }
1099
1100 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1101     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1102         self.as_ref().map(|t| t.fold_with(folder))
1103     }
1104 }
1105
1106 macro_rules! CloneImpls {
1107     (<$lt_tcx:tt> $($ty:ty),+) => {
1108         $(
1109             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1110                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1111                     Clone::clone(self)
1112                 }
1113             }
1114         )+
1115     }
1116 }
1117
1118 CloneImpls!{ <'tcx>
1119     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
1120     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
1121     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, UserTypeAnnotation<'tcx>,
1122     UserTypeProjection<'tcx>, PatternTypeProjection<'tcx>
1123 }
1124
1125 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1126     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1127         FieldPattern {
1128             field: self.field.fold_with(folder),
1129             pattern: self.pattern.fold_with(folder)
1130         }
1131     }
1132 }
1133
1134 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1135     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1136         folder.fold_pattern(self)
1137     }
1138
1139     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1140         Pattern {
1141             ty: self.ty.fold_with(folder),
1142             span: self.span.fold_with(folder),
1143             kind: self.kind.fold_with(folder)
1144         }
1145     }
1146 }
1147
1148 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1149     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1150         folder.fold_pattern_kind(self)
1151     }
1152
1153     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1154         match *self {
1155             PatternKind::Wild => PatternKind::Wild,
1156             PatternKind::AscribeUserType {
1157                 ref subpattern,
1158                 ref user_ty,
1159                 user_ty_span,
1160             } => PatternKind::AscribeUserType {
1161                 subpattern: subpattern.fold_with(folder),
1162                 user_ty: user_ty.fold_with(folder),
1163                 user_ty_span,
1164             },
1165             PatternKind::Binding {
1166                 mutability,
1167                 name,
1168                 mode,
1169                 var,
1170                 ty,
1171                 ref subpattern,
1172             } => PatternKind::Binding {
1173                 mutability: mutability.fold_with(folder),
1174                 name: name.fold_with(folder),
1175                 mode: mode.fold_with(folder),
1176                 var: var.fold_with(folder),
1177                 ty: ty.fold_with(folder),
1178                 subpattern: subpattern.fold_with(folder),
1179             },
1180             PatternKind::Variant {
1181                 adt_def,
1182                 substs,
1183                 variant_index,
1184                 ref subpatterns,
1185             } => PatternKind::Variant {
1186                 adt_def: adt_def.fold_with(folder),
1187                 substs: substs.fold_with(folder),
1188                 variant_index,
1189                 subpatterns: subpatterns.fold_with(folder)
1190             },
1191             PatternKind::Leaf {
1192                 ref subpatterns,
1193             } => PatternKind::Leaf {
1194                 subpatterns: subpatterns.fold_with(folder),
1195             },
1196             PatternKind::Deref {
1197                 ref subpattern,
1198             } => PatternKind::Deref {
1199                 subpattern: subpattern.fold_with(folder),
1200             },
1201             PatternKind::Constant {
1202                 value
1203             } => PatternKind::Constant {
1204                 value: value.fold_with(folder)
1205             },
1206             PatternKind::Range(PatternRange {
1207                 lo,
1208                 hi,
1209                 ty,
1210                 end,
1211             }) => PatternKind::Range(PatternRange {
1212                 lo: lo.fold_with(folder),
1213                 hi: hi.fold_with(folder),
1214                 ty: ty.fold_with(folder),
1215                 end,
1216             }),
1217             PatternKind::Slice {
1218                 ref prefix,
1219                 ref slice,
1220                 ref suffix,
1221             } => PatternKind::Slice {
1222                 prefix: prefix.fold_with(folder),
1223                 slice: slice.fold_with(folder),
1224                 suffix: suffix.fold_with(folder)
1225             },
1226             PatternKind::Array {
1227                 ref prefix,
1228                 ref slice,
1229                 ref suffix
1230             } => PatternKind::Array {
1231                 prefix: prefix.fold_with(folder),
1232                 slice: slice.fold_with(folder),
1233                 suffix: suffix.fold_with(folder)
1234             },
1235         }
1236     }
1237 }
1238
1239 pub fn compare_const_vals<'a, 'gcx, 'tcx>(
1240     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1241     a: &'tcx ty::Const<'tcx>,
1242     b: &'tcx ty::Const<'tcx>,
1243     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1244 ) -> Option<Ordering> {
1245     trace!("compare_const_vals: {:?}, {:?}", a, b);
1246
1247     let from_bool = |v: bool| {
1248         if v {
1249             Some(Ordering::Equal)
1250         } else {
1251             None
1252         }
1253     };
1254
1255     let fallback = || from_bool(a == b);
1256
1257     // Use the fallback if any type differs
1258     if a.ty != b.ty || a.ty != ty.value {
1259         return fallback();
1260     }
1261
1262     let tcx = tcx.global_tcx();
1263     let (a, b, ty) = (a, b, ty).lift_to_tcx(tcx).unwrap();
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(_) => {
1281                 let layout = tcx.layout_of(ty).ok()?;
1282                 assert!(layout.abi.is_signed());
1283                 let a = sign_extend(a, layout.size);
1284                 let b = sign_extend(b, layout.size);
1285                 Some((a as i128).cmp(&(b as i128)))
1286             },
1287             _ => Some(a.cmp(&b)),
1288         }
1289     }
1290
1291     if let ty::Str = ty.value.sty {
1292         match (a.val, b.val) {
1293             (
1294                 ConstValue::ScalarPair(
1295                     Scalar::Ptr(ptr_a),
1296                     len_a,
1297                 ),
1298                 ConstValue::ScalarPair(
1299                     Scalar::Ptr(ptr_b),
1300                     len_b,
1301                 ),
1302             ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1303                 if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1304                     if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1305                         if len_a == len_b {
1306                             let map = tcx.alloc_map.lock();
1307                             let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1308                             let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1309                             if alloc_a.bytes.len() as u128 == len_a {
1310                                 return from_bool(alloc_a == alloc_b);
1311                             }
1312                         }
1313                     }
1314                 }
1315             }
1316             _ => (),
1317         }
1318     }
1319
1320     fallback()
1321 }