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     fn map_projs(&self,
  83                  mut f: impl FnMut(&PatternTypeProjection<'tcx>) -> PatternTypeProjection<'tcx>)
  84                  -> Self
  85     {
  86         PatternTypeProjections {
  87             contents: self.contents
  88                 .iter()
  89                 .map(|(proj, span)| (f(proj), *span))
  90                 .collect(), }
  91     }
  92
  93     pub(crate) fn index(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.index()) }
  94
  95     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
  96         self.map_projs(|pat_ty_proj| pat_ty_proj.subslice(from, to))
  97     }
  98
  99     pub(crate) fn deref(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.deref()) }
 100
 101     pub(crate) fn leaf(&self, field: Field) -> Self {
 102         self.map_projs(|pat_ty_proj| pat_ty_proj.leaf(field))
 103     }
 104
 105     pub(crate) fn variant(&self,
 106                           adt_def: &'tcx AdtDef,
 107                           variant_index: VariantIdx,
 108                           field: Field) -> Self {
 109         self.map_projs(|pat_ty_proj| pat_ty_proj.variant(adt_def, variant_index, field))
 110     }
 111
 112     pub(crate) fn add_user_type(&self, user_ty: &PatternTypeProjection<'tcx>, sp: Span) -> Self {
 113         let mut new = self.clone();
 114         new.contents.push((user_ty.clone(), sp));
 115         new
 116     }
 117 }
 118
 119 #[derive(Clone, Debug)]
 120 pub struct PatternTypeProjection<'tcx> {
 121     pub base: CanonicalUserTypeAnnotation<'tcx>,
 122     pub projs: Vec<ProjectionElem<'tcx, (), ()>>,
 123 }
 124
 125 impl<'tcx> PatternTypeProjection<'tcx> {
 126     pub(crate) fn index(&self) -> Self {
 127         let mut new = self.clone();
 128         new.projs.push(ProjectionElem::Index(()));
 129         new
 130     }
 131
 132     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
 133         let mut new = self.clone();
 134         new.projs.push(ProjectionElem::Subslice { from, to });
 135         new
 136     }
 137
 138     pub(crate) fn deref(&self) -> Self {
 139         let mut new = self.clone();
 140         new.projs.push(ProjectionElem::Deref);
 141         new
 142     }
 143
 144     pub(crate) fn leaf(&self, field: Field) -> Self {
 145         let mut new = self.clone();
 146         new.projs.push(ProjectionElem::Field(field, ()));
 147         new
 148     }
 149
 150     pub(crate) fn variant(&self,
 151                           adt_def: &'tcx AdtDef,
 152                           variant_index: VariantIdx,
 153                           field: Field) -> Self {
 154         let mut new = self.clone();
 155         new.projs.push(ProjectionElem::Downcast(adt_def, variant_index));
 156         new.projs.push(ProjectionElem::Field(field, ()));
 157         new
 158     }
 159
 160     pub(crate) fn from_user_type(user_annotation: CanonicalUserTypeAnnotation<'tcx>) -> Self {
 161         Self {
 162             base: user_annotation,
 163             projs: Vec::new(),
 164         }
 165     }
 166
 167     pub(crate) fn user_ty(
 168         self,
 169         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
 170         span: Span,
 171     ) -> UserTypeProjection<'tcx> {
 172         let annotation_index = annotations.push((span, self.base));
 173         UserTypeProjection {
 174             base: annotation_index,
 175             projs: self.projs
 176         }
 177     }
 178 }
 179
 180 #[derive(Clone, Debug)]
 181 pub enum PatternKind<'tcx> {
 182     Wild,
 183
 184     AscribeUserType {
 185         user_ty: PatternTypeProjection<'tcx>,
 186         subpattern: Pattern<'tcx>,
 187         user_ty_span: Span,
 188     },
 189
 190     /// x, ref x, x @ P, etc
 191     Binding {
 192         mutability: Mutability,
 193         name: ast::Name,
 194         mode: BindingMode<'tcx>,
 195         var: ast::NodeId,
 196         ty: Ty<'tcx>,
 197         subpattern: Option<Pattern<'tcx>>,
 198     },
 199
 200     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
 201     Variant {
 202         adt_def: &'tcx AdtDef,
 203         substs: &'tcx Substs<'tcx>,
 204         variant_index: VariantIdx,
 205         subpatterns: Vec<FieldPattern<'tcx>>,
 206     },
 207
 208     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
 209     Leaf {
 210         subpatterns: Vec<FieldPattern<'tcx>>,
 211     },
 212
 213     /// box P, &P, &mut P, etc
 214     Deref {
 215         subpattern: Pattern<'tcx>,
 216     },
 217
 218     Constant {
 219         value: &'tcx ty::Const<'tcx>,
 220     },
 221
 222     Range(PatternRange<'tcx>),
 223
 224     /// matches against a slice, checking the length and extracting elements.
 225     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 226     /// e.g., `&[ref xs..]`.
 227     Slice {
 228         prefix: Vec<Pattern<'tcx>>,
 229         slice: Option<Pattern<'tcx>>,
 230         suffix: Vec<Pattern<'tcx>>,
 231     },
 232
 233     /// fixed match against an array, irrefutable
 234     Array {
 235         prefix: Vec<Pattern<'tcx>>,
 236         slice: Option<Pattern<'tcx>>,
 237         suffix: Vec<Pattern<'tcx>>,
 238     },
 239 }
 240
 241 #[derive(Clone, Copy, Debug, PartialEq)]
 242 pub struct PatternRange<'tcx> {
 243     pub lo: &'tcx ty::Const<'tcx>,
 244     pub hi: &'tcx ty::Const<'tcx>,
 245     pub ty: Ty<'tcx>,
 246     pub end: RangeEnd,
 247 }
 248
 249 impl<'tcx> fmt::Display for Pattern<'tcx> {
 250     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 251         match *self.kind {
 252             PatternKind::Wild => write!(f, "_"),
 253             PatternKind::AscribeUserType { ref subpattern, .. } =>
 254                 write!(f, "{}: _", subpattern),
 255             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 256                 let is_mut = match mode {
 257                     BindingMode::ByValue => mutability == Mutability::Mut,
 258                     BindingMode::ByRef(_, bk) => {
 259                         write!(f, "ref ")?;
 260                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 261                     }
 262                 };
 263                 if is_mut {
 264                     write!(f, "mut ")?;
 265                 }
 266                 write!(f, "{}", name)?;
 267                 if let Some(ref subpattern) = *subpattern {
 268                     write!(f, " @ {}", subpattern)?;
 269                 }
 270                 Ok(())
 271             }
 272             PatternKind::Variant { ref subpatterns, .. } |
 273             PatternKind::Leaf { ref subpatterns } => {
 274                 let variant = match *self.kind {
 275                     PatternKind::Variant { adt_def, variant_index, .. } => {
 276                         Some(&adt_def.variants[variant_index])
 277                     }
 278                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 279                         if !adt.is_enum() {
 280                             Some(&adt.variants[VariantIdx::new(0)])
 281                         } else {
 282                             None
 283                         }
 284                     } else {
 285                         None
 286                     }
 287                 };
 288
 289                 let mut first = true;
 290                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 291
 292                 if let Some(variant) = variant {
 293                     write!(f, "{}", variant.ident)?;
 294
 295                     // Only for Adt we can have `S {...}`,
 296                     // which we handle separately here.
 297                     if variant.ctor_kind == CtorKind::Fictive {
 298                         write!(f, " {{ ")?;
 299
 300                         let mut printed = 0;
 301                         for p in subpatterns {
 302                             if let PatternKind::Wild = *p.pattern.kind {
 303                                 continue;
 304                             }
 305                             let name = variant.fields[p.field.index()].ident;
 306                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 307                             printed += 1;
 308                         }
 309
 310                         if printed < variant.fields.len() {
 311                             write!(f, "{}..", start_or_continue())?;
 312                         }
 313
 314                         return write!(f, " }}");
 315                     }
 316                 }
 317
 318                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 319                 if num_fields != 0 || variant.is_none() {
 320                     write!(f, "(")?;
 321                     for i in 0..num_fields {
 322                         write!(f, "{}", start_or_continue())?;
 323
 324                         // Common case: the field is where we expect it.
 325                         if let Some(p) = subpatterns.get(i) {
 326                             if p.field.index() == i {
 327                                 write!(f, "{}", p.pattern)?;
 328                                 continue;
 329                             }
 330                         }
 331
 332                         // Otherwise, we have to go looking for it.
 333                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 334                             write!(f, "{}", p.pattern)?;
 335                         } else {
 336                             write!(f, "_")?;
 337                         }
 338                     }
 339                     write!(f, ")")?;
 340                 }
 341
 342                 Ok(())
 343             }
 344             PatternKind::Deref { ref subpattern } => {
 345                 match self.ty.sty {
 346                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 347                     ty::Ref(_, _, mutbl) => {
 348                         write!(f, "&")?;
 349                         if mutbl == hir::MutMutable {
 350                             write!(f, "mut ")?;
 351                         }
 352                     }
 353                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 354                 }
 355                 write!(f, "{}", subpattern)
 356             }
 357             PatternKind::Constant { value } => {
 358                 fmt_const_val(f, value)
 359             }
 360             PatternKind::Range(PatternRange { lo, hi, ty: _, end }) => {
 361                 fmt_const_val(f, lo)?;
 362                 match end {
 363                     RangeEnd::Included => write!(f, "..=")?,
 364                     RangeEnd::Excluded => write!(f, "..")?,
 365                 }
 366                 fmt_const_val(f, hi)
 367             }
 368             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 369             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 370                 let mut first = true;
 371                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 372                 write!(f, "[")?;
 373                 for p in prefix {
 374                     write!(f, "{}{}", start_or_continue(), p)?;
 375                 }
 376                 if let Some(ref slice) = *slice {
 377                     write!(f, "{}", start_or_continue())?;
 378                     match *slice.kind {
 379                         PatternKind::Wild => {}
 380                         _ => write!(f, "{}", slice)?
 381                     }
 382                     write!(f, "..")?;
 383                 }
 384                 for p in suffix {
 385                     write!(f, "{}{}", start_or_continue(), p)?;
 386                 }
 387                 write!(f, "]")
 388             }
 389         }
 390     }
 391 }
 392
 393 pub struct PatternContext<'a, 'tcx: 'a> {
 394     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 395     pub param_env: ty::ParamEnv<'tcx>,
 396     pub tables: &'a ty::TypeckTables<'tcx>,
 397     pub substs: &'tcx Substs<'tcx>,
 398     pub errors: Vec<PatternError>,
 399 }
 400
 401 impl<'a, 'tcx> Pattern<'tcx> {
 402     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 403                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 404                     tables: &'a ty::TypeckTables<'tcx>,
 405                     pat: &'tcx hir::Pat) -> Self {
 406         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 407         let result = pcx.lower_pattern(pat);
 408         if !pcx.errors.is_empty() {
 409             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 410             tcx.sess.delay_span_bug(pat.span, &msg);
 411         }
 412         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 413         result
 414     }
 415 }
 416
 417 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 418     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 419                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 420                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 421         PatternContext {
 422             tcx,
 423             param_env: param_env_and_substs.param_env,
 424             tables,
 425             substs: param_env_and_substs.value,
 426             errors: vec![]
 427         }
 428     }
 429
 430     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 431         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 432         // pattern has the type that results *after* dereferencing. For example, in this code:
 433         //
 434         // ```
 435         // match &&Some(0i32) {
 436         //     Some(n) => { ... },
 437         //     _ => { ... },
 438         // }
 439         // ```
 440         //
 441         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 442         // determined in rustc_typeck::check::match). The adjustments would be
 443         //
 444         // `vec![&&Option<i32>, &Option<i32>]`.
 445         //
 446         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 447         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 448         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 449         // gets the least-dereferenced type).
 450         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 451         self.tables
 452             .pat_adjustments()
 453             .get(pat.hir_id)
 454             .unwrap_or(&vec![])
 455             .iter()
 456             .rev()
 457             .fold(unadjusted_pat, |pat, ref_ty| {
 458                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 459                     Pattern {
 460                         span: pat.span,
 461                         ty: ref_ty,
 462                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 463                     }
 464                 },
 465             )
 466     }
 467
 468     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 469         let mut ty = self.tables.node_id_to_type(pat.hir_id);
 470
 471         let kind = match pat.node {
 472             PatKind::Wild => PatternKind::Wild,
 473
 474             PatKind::Lit(ref value) => self.lower_lit(value),
 475
 476             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 477                 match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
 478                     (PatternKind::Constant { value: lo },
 479                      PatternKind::Constant { value: hi }) => {
 480                         use std::cmp::Ordering;
 481                         let cmp = compare_const_vals(
 482                             self.tcx,
 483                             lo,
 484                             hi,
 485                             self.param_env.and(ty),
 486                         );
 487                         match (end, cmp) {
 488                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 489                                 PatternKind::Range(PatternRange { lo, hi, ty, end }),
 490                             (RangeEnd::Excluded, _) => {
 491                                 span_err!(
 492                                     self.tcx.sess,
 493                                     lo_expr.span,
 494                                     E0579,
 495                                     "lower range bound must be less than upper",
 496                                 );
 497                                 PatternKind::Wild
 498                             }
 499                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 500                                 PatternKind::Constant { value: lo }
 501                             }
 502                             (RangeEnd::Included, Some(Ordering::Less)) => {
 503                                 PatternKind::Range(PatternRange { lo, hi, ty, end })
 504                             }
 505                             (RangeEnd::Included, _) => {
 506                                 let mut err = struct_span_err!(
 507                                     self.tcx.sess,
 508                                     lo_expr.span,
 509                                     E0030,
 510                                     "lower range bound must be less than or equal to upper"
 511                                 );
 512                                 err.span_label(
 513                                     lo_expr.span,
 514                                     "lower bound larger than upper bound",
 515                                 );
 516                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 517                                     err.note("When matching against a range, the compiler \
 518                                               verifies that the range is non-empty. Range \
 519                                               patterns include both end-points, so this is \
 520                                               equivalent to requiring the start of the range \
 521                                               to be less than or equal to the end of the range.");
 522                                 }
 523                                 err.emit();
 524                                 PatternKind::Wild
 525                             }
 526                         }
 527                     }
 528                     _ => PatternKind::Wild
 529                 }
 530             }
 531
 532             PatKind::Path(ref qpath) => {
 533                 return self.lower_path(qpath, pat.hir_id, pat.span);
 534             }
 535
 536             PatKind::Ref(ref subpattern, _) |
 537             PatKind::Box(ref subpattern) => {
 538                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 539             }
 540
 541             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 542                 match ty.sty {
 543                     ty::Ref(_, ty, _) =>
 544                         PatternKind::Deref {
 545                             subpattern: Pattern {
 546                                 ty,
 547                                 span: pat.span,
 548                                 kind: Box::new(self.slice_or_array_pattern(
 549                                     pat.span, ty, prefix, slice, suffix))
 550                             },
 551                         },
 552                     ty::Slice(..) |
 553                     ty::Array(..) =>
 554                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 555                     ty::Error => { // Avoid ICE
 556                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 557                     }
 558                     ref sty =>
 559                         span_bug!(
 560                             pat.span,
 561                             "unexpanded type for vector pattern: {:?}",
 562                             sty),
 563                 }
 564             }
 565
 566             PatKind::Tuple(ref subpatterns, ddpos) => {
 567                 match ty.sty {
 568                     ty::Tuple(ref tys) => {
 569                         let subpatterns =
 570                             subpatterns.iter()
 571                                        .enumerate_and_adjust(tys.len(), ddpos)
 572                                        .map(|(i, subpattern)| FieldPattern {
 573                                             field: Field::new(i),
 574                                             pattern: self.lower_pattern(subpattern)
 575                                        })
 576                                        .collect();
 577
 578                         PatternKind::Leaf { subpatterns }
 579                     }
 580                     ty::Error => { // Avoid ICE (#50577)
 581                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 582                     }
 583                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 584                 }
 585             }
 586
 587             PatKind::Binding(_, id, ident, ref sub) => {
 588                 let var_ty = self.tables.node_id_to_type(pat.hir_id);
 589                 let region = match var_ty.sty {
 590                     ty::Ref(r, _, _) => Some(r),
 591                     ty::Error => { // Avoid ICE
 592                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 593                     }
 594                     _ => None,
 595                 };
 596                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 597                                                          .expect("missing binding mode");
 598                 let (mutability, mode) = match bm {
 599                     ty::BindByValue(hir::MutMutable) =>
 600                         (Mutability::Mut, BindingMode::ByValue),
 601                     ty::BindByValue(hir::MutImmutable) =>
 602                         (Mutability::Not, BindingMode::ByValue),
 603                     ty::BindByReference(hir::MutMutable) =>
 604                         (Mutability::Not, BindingMode::ByRef(
 605                             region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
 606                     ty::BindByReference(hir::MutImmutable) =>
 607                         (Mutability::Not, BindingMode::ByRef(
 608                             region.unwrap(), BorrowKind::Shared)),
 609                 };
 610
 611                 // A ref x pattern is the same node used for x, and as such it has
 612                 // x's type, which is &T, where we want T (the type being matched).
 613                 if let ty::BindByReference(_) = bm {
 614                     if let ty::Ref(_, rty, _) = ty.sty {
 615                         ty = rty;
 616                     } else {
 617                         bug!("`ref {}` has wrong type {}", ident, ty);
 618                     }
 619                 }
 620
 621                 PatternKind::Binding {
 622                     mutability,
 623                     mode,
 624                     name: ident.name,
 625                     var: id,
 626                     ty: var_ty,
 627                     subpattern: self.lower_opt_pattern(sub),
 628                 }
 629             }
 630
 631             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 632                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 633                 let adt_def = match ty.sty {
 634                     ty::Adt(adt_def, _) => adt_def,
 635                     ty::Error => { // Avoid ICE (#50585)
 636                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 637                     }
 638                     _ => span_bug!(pat.span,
 639                                    "tuple struct pattern not applied to an ADT {:?}",
 640                                    ty.sty),
 641                 };
 642                 let variant_def = adt_def.variant_of_def(def);
 643
 644                 let subpatterns =
 645                         subpatterns.iter()
 646                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 647                                    .map(|(i, field)| FieldPattern {
 648                                        field: Field::new(i),
 649                                        pattern: self.lower_pattern(field),
 650                                    })
 651                     .collect();
 652
 653                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 654             }
 655
 656             PatKind::Struct(ref qpath, ref fields, _) => {
 657                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 658                 let subpatterns =
 659                     fields.iter()
 660                           .map(|field| {
 661                               FieldPattern {
 662                                   field: Field::new(self.tcx.field_index(field.node.id,
 663                                                                          self.tables)),
 664                                   pattern: self.lower_pattern(&field.node.pat),
 665                               }
 666                           })
 667                           .collect();
 668
 669                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 670             }
 671         };
 672
 673         Pattern {
 674             span: pat.span,
 675             ty,
 676             kind: Box::new(kind),
 677         }
 678     }
 679
 680     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 681         pats.iter().map(|p| self.lower_pattern(p)).collect()
 682     }
 683
 684     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 685     {
 686         pat.as_ref().map(|p| self.lower_pattern(p))
 687     }
 688
 689     fn flatten_nested_slice_patterns(
 690         &mut self,
 691         prefix: Vec<Pattern<'tcx>>,
 692         slice: Option<Pattern<'tcx>>,
 693         suffix: Vec<Pattern<'tcx>>)
 694         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 695     {
 696         let orig_slice = match slice {
 697             Some(orig_slice) => orig_slice,
 698             None => return (prefix, slice, suffix)
 699         };
 700         let orig_prefix = prefix;
 701         let orig_suffix = suffix;
 702
 703         // dance because of intentional borrow-checker stupidity.
 704         let kind = *orig_slice.kind;
 705         match kind {
 706             PatternKind::Slice { prefix, slice, mut suffix } |
 707             PatternKind::Array { prefix, slice, mut suffix } => {
 708                 let mut orig_prefix = orig_prefix;
 709
 710                 orig_prefix.extend(prefix);
 711                 suffix.extend(orig_suffix);
 712
 713                 (orig_prefix, slice, suffix)
 714             }
 715             _ => {
 716                 (orig_prefix, Some(Pattern {
 717                     kind: box kind, ..orig_slice
 718                 }), orig_suffix)
 719             }
 720         }
 721     }
 722
 723     fn slice_or_array_pattern(
 724         &mut self,
 725         span: Span,
 726         ty: Ty<'tcx>,
 727         prefix: &'tcx [P<hir::Pat>],
 728         slice: &'tcx Option<P<hir::Pat>>,
 729         suffix: &'tcx [P<hir::Pat>])
 730         -> PatternKind<'tcx>
 731     {
 732         let prefix = self.lower_patterns(prefix);
 733         let slice = self.lower_opt_pattern(slice);
 734         let suffix = self.lower_patterns(suffix);
 735         let (prefix, slice, suffix) =
 736             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 737
 738         match ty.sty {
 739             ty::Slice(..) => {
 740                 // matching a slice or fixed-length array
 741                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 742             }
 743
 744             ty::Array(_, len) => {
 745                 // fixed-length array
 746                 let len = len.unwrap_usize(self.tcx);
 747                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 748                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 749             }
 750
 751             _ => {
 752                 span_bug!(span, "bad slice pattern type {:?}", ty);
 753             }
 754         }
 755     }
 756
 757     fn lower_variant_or_leaf(
 758         &mut self,
 759         def: Def,
 760         hir_id: hir::HirId,
 761         span: Span,
 762         ty: Ty<'tcx>,
 763         subpatterns: Vec<FieldPattern<'tcx>>,
 764     ) -> PatternKind<'tcx> {
 765         let mut kind = match def {
 766             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 767                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 768                 let adt_def = self.tcx.adt_def(enum_id);
 769                 if adt_def.is_enum() {
 770                     let substs = match ty.sty {
 771                         ty::Adt(_, substs) |
 772                         ty::FnDef(_, substs) => substs,
 773                         ty::Error => {  // Avoid ICE (#50585)
 774                             return PatternKind::Wild;
 775                         }
 776                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 777                     };
 778                     PatternKind::Variant {
 779                         adt_def,
 780                         substs,
 781                         variant_index: adt_def.variant_index_with_id(variant_id),
 782                         subpatterns,
 783                     }
 784                 } else {
 785                     PatternKind::Leaf { subpatterns }
 786                 }
 787             }
 788
 789             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 790             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) => {
 791                 PatternKind::Leaf { subpatterns }
 792             }
 793
 794             _ => {
 795                 self.errors.push(PatternError::NonConstPath(span));
 796                 PatternKind::Wild
 797             }
 798         };
 799
 800         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 801             debug!("lower_variant_or_leaf: kind={:?} user_ty={:?} span={:?}", kind, user_ty, span);
 802             kind = PatternKind::AscribeUserType {
 803                 subpattern: Pattern {
 804                     span,
 805                     ty,
 806                     kind: Box::new(kind),
 807                 },
 808                 user_ty: PatternTypeProjection::from_user_type(user_ty),
 809                 user_ty_span: span,
 810             };
 811         }
 812
 813         kind
 814     }
 815
 816     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 817     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 818     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 819     fn lower_path(&mut self,
 820                   qpath: &hir::QPath,
 821                   id: hir::HirId,
 822                   span: Span)
 823                   -> Pattern<'tcx> {
 824         let ty = self.tables.node_id_to_type(id);
 825         let def = self.tables.qpath_def(qpath, id);
 826         let is_associated_const = match def {
 827             Def::AssociatedConst(_) => true,
 828             _ => false,
 829         };
 830         let kind = match def {
 831             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 832                 let substs = self.tables.node_substs(id);
 833                 match ty::Instance::resolve(
 834                     self.tcx,
 835                     self.param_env,
 836                     def_id,
 837                     substs,
 838                 ) {
 839                     Some(instance) => {
 840                         let cid = GlobalId {
 841                             instance,
 842                             promoted: None,
 843                         };
 844                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 845                             Ok(value) => {
 846                                 let pattern = self.const_to_pat(instance, value, id, span);
 847                                 if !is_associated_const {
 848                                     return pattern;
 849                                 }
 850
 851                                 let user_provided_types = self.tables().user_provided_types();
 852                                 return if let Some(u_ty) = user_provided_types.get(id) {
 853                                     let user_ty = PatternTypeProjection::from_user_type(*u_ty);
 854                                     Pattern {
 855                                         span,
 856                                         kind: Box::new(
 857                                             PatternKind::AscribeUserType {
 858                                                 subpattern: pattern,
 859                                                 user_ty,
 860                                                 user_ty_span: span,
 861                                             }
 862                                         ),
 863                                         ty: value.ty,
 864                                     }
 865                                 } else {
 866                                     pattern
 867                                 }
 868                             },
 869                             Err(_) => {
 870                                 self.tcx.sess.span_err(
 871                                     span,
 872                                     "could not evaluate constant pattern",
 873                                 );
 874                                 PatternKind::Wild
 875                             }
 876                         }
 877                     },
 878                     None => {
 879                         self.errors.push(if is_associated_const {
 880                             PatternError::AssociatedConstInPattern(span)
 881                         } else {
 882                             PatternError::StaticInPattern(span)
 883                         });
 884                         PatternKind::Wild
 885                     },
 886                 }
 887             }
 888             _ => self.lower_variant_or_leaf(def, id, span, ty, vec![]),
 889         };
 890
 891         Pattern {
 892             span,
 893             ty,
 894             kind: Box::new(kind),
 895         }
 896     }
 897
 898     /// Converts literals, paths and negation of literals to patterns.
 899     /// The special case for negation exists to allow things like -128i8
 900     /// which would overflow if we tried to evaluate 128i8 and then negate
 901     /// afterwards.
 902     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 903         match expr.node {
 904             hir::ExprKind::Lit(ref lit) => {
 905                 let ty = self.tables.expr_ty(expr);
 906                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 907                     Ok(val) => {
 908                         let instance = ty::Instance::new(
 909                             self.tables.local_id_root.expect("literal outside any scope"),
 910                             self.substs,
 911                         );
 912                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 913                     },
 914                     Err(LitToConstError::UnparseableFloat) => {
 915                         self.errors.push(PatternError::FloatBug);
 916                         PatternKind::Wild
 917                     },
 918                     Err(LitToConstError::Reported) => PatternKind::Wild,
 919                 }
 920             },
 921             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 922             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 923                 let ty = self.tables.expr_ty(expr);
 924                 let lit = match expr.node {
 925                     hir::ExprKind::Lit(ref lit) => lit,
 926                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 927                 };
 928                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 929                     Ok(val) => {
 930                         let instance = ty::Instance::new(
 931                             self.tables.local_id_root.expect("literal outside any scope"),
 932                             self.substs,
 933                         );
 934                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 935                     },
 936                     Err(LitToConstError::UnparseableFloat) => {
 937                         self.errors.push(PatternError::FloatBug);
 938                         PatternKind::Wild
 939                     },
 940                     Err(LitToConstError::Reported) => PatternKind::Wild,
 941                 }
 942             }
 943             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 944         }
 945     }
 946
 947     /// Converts an evaluated constant to a pattern (if possible).
 948     /// This means aggregate values (like structs and enums) are converted
 949     /// to a pattern that matches the value (as if you'd compare via eq).
 950     fn const_to_pat(
 951         &self,
 952         instance: ty::Instance<'tcx>,
 953         cv: &'tcx ty::Const<'tcx>,
 954         id: hir::HirId,
 955         span: Span,
 956     ) -> Pattern<'tcx> {
 957         debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
 958         let adt_subpattern = |i, variant_opt| {
 959             let field = Field::new(i);
 960             let val = const_field(
 961                 self.tcx, self.param_env, instance,
 962                 variant_opt, field, cv,
 963             ).expect("field access failed");
 964             self.const_to_pat(instance, val, id, span)
 965         };
 966         let adt_subpatterns = |n, variant_opt| {
 967             (0..n).map(|i| {
 968                 let field = Field::new(i);
 969                 FieldPattern {
 970                     field,
 971                     pattern: adt_subpattern(i, variant_opt),
 972                 }
 973             }).collect::<Vec<_>>()
 974         };
 975         debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
 976         let kind = match cv.ty.sty {
 977             ty::Float(_) => {
 978                 let id = self.tcx.hir().hir_to_node_id(id);
 979                 self.tcx.lint_node(
 980                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 981                     id,
 982                     span,
 983                     "floating-point types cannot be used in patterns",
 984                 );
 985                 PatternKind::Constant {
 986                     value: cv,
 987                 }
 988             },
 989             ty::Adt(adt_def, _) if adt_def.is_union() => {
 990                 // Matching on union fields is unsafe, we can't hide it in constants
 991                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 992                 PatternKind::Wild
 993             }
 994             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 995                 let msg = format!("to use a constant of type `{}` in a pattern, \
 996                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 997                                     self.tcx.item_path_str(adt_def.did),
 998                                     self.tcx.item_path_str(adt_def.did));
 999                 self.tcx.sess.span_err(span, &msg);
1000                 PatternKind::Wild
1001             },
1002             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
1003                 let variant_index = const_variant_index(
1004                     self.tcx, self.param_env, instance, cv
1005                 ).expect("const_variant_index failed");
1006                 let subpatterns = adt_subpatterns(
1007                     adt_def.variants[variant_index].fields.len(),
1008                     Some(variant_index),
1009                 );
1010                 PatternKind::Variant {
1011                     adt_def,
1012                     substs,
1013                     variant_index,
1014                     subpatterns,
1015                 }
1016             },
1017             ty::Adt(adt_def, _) => {
1018                 let struct_var = adt_def.non_enum_variant();
1019                 PatternKind::Leaf {
1020                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
1021                 }
1022             }
1023             ty::Tuple(fields) => {
1024                 PatternKind::Leaf {
1025                     subpatterns: adt_subpatterns(fields.len(), None),
1026                 }
1027             }
1028             ty::Array(_, n) => {
1029                 PatternKind::Array {
1030                     prefix: (0..n.unwrap_usize(self.tcx))
1031                         .map(|i| adt_subpattern(i as usize, None))
1032                         .collect(),
1033                     slice: None,
1034                     suffix: Vec::new(),
1035                 }
1036             }
1037             _ => {
1038                 PatternKind::Constant {
1039                     value: cv,
1040                 }
1041             },
1042         };
1043
1044         Pattern {
1045             span,
1046             ty: cv.ty,
1047             kind: Box::new(kind),
1048         }
1049     }
1050 }
1051
1052 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
1053     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
1054         self.tcx
1055     }
1056
1057     fn tables(&self) -> &ty::TypeckTables<'tcx> {
1058         self.tables
1059     }
1060 }
1061
1062
1063 pub trait PatternFoldable<'tcx> : Sized {
1064     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1065         self.super_fold_with(folder)
1066     }
1067
1068     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
1069 }
1070
1071 pub trait PatternFolder<'tcx> : Sized {
1072     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
1073         pattern.super_fold_with(self)
1074     }
1075
1076     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
1077         kind.super_fold_with(self)
1078     }
1079 }
1080
1081
1082 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
1083     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1084         let content: T = (**self).fold_with(folder);
1085         box content
1086     }
1087 }
1088
1089 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1090     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1091         self.iter().map(|t| t.fold_with(folder)).collect()
1092     }
1093 }
1094
1095 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1096     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1097         self.as_ref().map(|t| t.fold_with(folder))
1098     }
1099 }
1100
1101 macro_rules! CloneImpls {
1102     (<$lt_tcx:tt> $($ty:ty),+) => {
1103         $(
1104             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1105                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1106                     Clone::clone(self)
1107                 }
1108             }
1109         )+
1110     }
1111 }
1112
1113 CloneImpls!{ <'tcx>
1114     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
1115     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
1116     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, UserTypeAnnotation<'tcx>,
1117     UserTypeProjection<'tcx>, PatternTypeProjection<'tcx>
1118 }
1119
1120 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1121     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1122         FieldPattern {
1123             field: self.field.fold_with(folder),
1124             pattern: self.pattern.fold_with(folder)
1125         }
1126     }
1127 }
1128
1129 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1130     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1131         folder.fold_pattern(self)
1132     }
1133
1134     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1135         Pattern {
1136             ty: self.ty.fold_with(folder),
1137             span: self.span.fold_with(folder),
1138             kind: self.kind.fold_with(folder)
1139         }
1140     }
1141 }
1142
1143 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1144     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1145         folder.fold_pattern_kind(self)
1146     }
1147
1148     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1149         match *self {
1150             PatternKind::Wild => PatternKind::Wild,
1151             PatternKind::AscribeUserType {
1152                 ref subpattern,
1153                 ref user_ty,
1154                 user_ty_span,
1155             } => PatternKind::AscribeUserType {
1156                 subpattern: subpattern.fold_with(folder),
1157                 user_ty: user_ty.fold_with(folder),
1158                 user_ty_span,
1159             },
1160             PatternKind::Binding {
1161                 mutability,
1162                 name,
1163                 mode,
1164                 var,
1165                 ty,
1166                 ref subpattern,
1167             } => PatternKind::Binding {
1168                 mutability: mutability.fold_with(folder),
1169                 name: name.fold_with(folder),
1170                 mode: mode.fold_with(folder),
1171                 var: var.fold_with(folder),
1172                 ty: ty.fold_with(folder),
1173                 subpattern: subpattern.fold_with(folder),
1174             },
1175             PatternKind::Variant {
1176                 adt_def,
1177                 substs,
1178                 variant_index,
1179                 ref subpatterns,
1180             } => PatternKind::Variant {
1181                 adt_def: adt_def.fold_with(folder),
1182                 substs: substs.fold_with(folder),
1183                 variant_index,
1184                 subpatterns: subpatterns.fold_with(folder)
1185             },
1186             PatternKind::Leaf {
1187                 ref subpatterns,
1188             } => PatternKind::Leaf {
1189                 subpatterns: subpatterns.fold_with(folder),
1190             },
1191             PatternKind::Deref {
1192                 ref subpattern,
1193             } => PatternKind::Deref {
1194                 subpattern: subpattern.fold_with(folder),
1195             },
1196             PatternKind::Constant {
1197                 value
1198             } => PatternKind::Constant {
1199                 value: value.fold_with(folder)
1200             },
1201             PatternKind::Range(PatternRange {
1202                 lo,
1203                 hi,
1204                 ty,
1205                 end,
1206             }) => PatternKind::Range(PatternRange {
1207                 lo: lo.fold_with(folder),
1208                 hi: hi.fold_with(folder),
1209                 ty: ty.fold_with(folder),
1210                 end,
1211             }),
1212             PatternKind::Slice {
1213                 ref prefix,
1214                 ref slice,
1215                 ref suffix,
1216             } => PatternKind::Slice {
1217                 prefix: prefix.fold_with(folder),
1218                 slice: slice.fold_with(folder),
1219                 suffix: suffix.fold_with(folder)
1220             },
1221             PatternKind::Array {
1222                 ref prefix,
1223                 ref slice,
1224                 ref suffix
1225             } => PatternKind::Array {
1226                 prefix: prefix.fold_with(folder),
1227                 slice: slice.fold_with(folder),
1228                 suffix: suffix.fold_with(folder)
1229             },
1230         }
1231     }
1232 }
1233
1234 pub fn compare_const_vals<'a, 'gcx, 'tcx>(
1235     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1236     a: &'tcx ty::Const<'tcx>,
1237     b: &'tcx ty::Const<'tcx>,
1238     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1239 ) -> Option<Ordering> {
1240     trace!("compare_const_vals: {:?}, {:?}", a, b);
1241
1242     let from_bool = |v: bool| {
1243         if v {
1244             Some(Ordering::Equal)
1245         } else {
1246             None
1247         }
1248     };
1249
1250     let fallback = || from_bool(a == b);
1251
1252     // Use the fallback if any type differs
1253     if a.ty != b.ty || a.ty != ty.value {
1254         return fallback();
1255     }
1256
1257     let tcx = tcx.global_tcx();
1258     let (a, b, ty) = (a, b, ty).lift_to_tcx(tcx).unwrap();
1259
1260     // FIXME: This should use assert_bits(ty) instead of use_bits
1261     // but triggers possibly bugs due to mismatching of arrays and slices
1262     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1263         use ::rustc_apfloat::Float;
1264         return match ty.value.sty {
1265             ty::Float(ast::FloatTy::F32) => {
1266                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1267                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1268                 l.partial_cmp(&r)
1269             },
1270             ty::Float(ast::FloatTy::F64) => {
1271                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1272                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1273                 l.partial_cmp(&r)
1274             },
1275             ty::Int(_) => {
1276                 let layout = tcx.layout_of(ty).ok()?;
1277                 assert!(layout.abi.is_signed());
1278                 let a = sign_extend(a, layout.size);
1279                 let b = sign_extend(b, layout.size);
1280                 Some((a as i128).cmp(&(b as i128)))
1281             },
1282             _ => Some(a.cmp(&b)),
1283         }
1284     }
1285
1286     if let ty::Str = ty.value.sty {
1287         match (a.val, b.val) {
1288             (
1289                 ConstValue::ScalarPair(
1290                     Scalar::Ptr(ptr_a),
1291                     len_a,
1292                 ),
1293                 ConstValue::ScalarPair(
1294                     Scalar::Ptr(ptr_b),
1295                     len_b,
1296                 ),
1297             ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1298                 if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1299                     if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1300                         if len_a == len_b {
1301                             let map = tcx.alloc_map.lock();
1302                             let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1303                             let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1304                             if alloc_a.bytes.len() as u128 == len_a {
1305                                 return from_bool(alloc_a == alloc_b);
1306                             }
1307                         }
1308                     }
1309                 }
1310             }
1311             _ => (),
1312         }
1313     }
1314
1315     fallback()
1316 }