src/librustc_mir/hair/pattern/mod.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Code to validate patterns/matches
  12
  13 mod _match;
  14 mod check_match;
  15
  16 pub use self::check_match::check_crate;
  17 pub(crate) use self::check_match::check_match;
  18
  19 use const_eval::{const_field, const_variant_index};
  20
  21 use hair::util::UserAnnotatedTyHelpers;
  22 use hair::constant::*;
  23
  24 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability};
  25 use rustc::mir::{ProjectionElem, UserTypeAnnotation, UserTypeProjection, UserTypeProjections};
  26 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  27 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, Lift};
  28 use rustc::ty::subst::{Substs, Kind};
  29 use rustc::ty::layout::VariantIdx;
  30 use rustc::hir::{self, PatKind, RangeEnd};
  31 use rustc::hir::def::{Def, CtorKind};
  32 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  33
  34 use rustc_data_structures::indexed_vec::Idx;
  35
  36 use std::cmp::Ordering;
  37 use std::fmt;
  38 use syntax::ast;
  39 use syntax::ptr::P;
  40 use syntax_pos::Span;
  41
  42 #[derive(Clone, Debug)]
  43 pub enum PatternError {
  44     AssociatedConstInPattern(Span),
  45     StaticInPattern(Span),
  46     FloatBug,
  47     NonConstPath(Span),
  48 }
  49
  50 #[derive(Copy, Clone, Debug)]
  51 pub enum BindingMode<'tcx> {
  52     ByValue,
  53     ByRef(Region<'tcx>, BorrowKind),
  54 }
  55
  56 #[derive(Clone, Debug)]
  57 pub struct FieldPattern<'tcx> {
  58     pub field: Field,
  59     pub pattern: Pattern<'tcx>,
  60 }
  61
  62 #[derive(Clone, Debug)]
  63 pub struct Pattern<'tcx> {
  64     pub ty: Ty<'tcx>,
  65     pub span: Span,
  66     pub kind: Box<PatternKind<'tcx>>,
  67 }
  68
  69
  70 #[derive(Clone, Debug)]
  71 pub(crate) struct PatternTypeProjections<'tcx> {
  72     contents: Vec<(PatternTypeProjection<'tcx>, Span)>,
  73 }
  74
  75 impl<'tcx> PatternTypeProjections<'tcx> {
  76     pub(crate) fn user_ty(self) -> UserTypeProjections<'tcx> {
  77         UserTypeProjections::from_projections(
  78             self.contents.into_iter().map(|(pat_ty_proj, span)| (pat_ty_proj.user_ty(), span)))
  79     }
  80
  81     pub(crate) fn none() -> Self {
  82         PatternTypeProjections { contents: vec![] }
  83     }
  84
  85     pub(crate) fn ref_binding(&self) -> Self {
  86         // FIXME(#47184): ignore for now
  87         PatternTypeProjections { contents: vec![] }
  88     }
  89
  90     fn map_projs(&self,
  91                  mut f: impl FnMut(&PatternTypeProjection<'tcx>) -> PatternTypeProjection<'tcx>)
  92                  -> Self
  93     {
  94         PatternTypeProjections {
  95             contents: self.contents
  96                 .iter()
  97                 .map(|(proj, span)| (f(proj), *span))
  98                 .collect(), }
  99     }
 100
 101     pub(crate) fn index(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.index()) }
 102
 103     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
 104         self.map_projs(|pat_ty_proj| pat_ty_proj.subslice(from, to))
 105     }
 106
 107     pub(crate) fn deref(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.deref()) }
 108
 109     pub(crate) fn leaf(&self, field: Field) -> Self {
 110         self.map_projs(|pat_ty_proj| pat_ty_proj.leaf(field))
 111     }
 112
 113     pub(crate) fn variant(&self,
 114                           adt_def: &'tcx AdtDef,
 115                           variant_index: VariantIdx,
 116                           field: Field) -> Self {
 117         self.map_projs(|pat_ty_proj| pat_ty_proj.variant(adt_def, variant_index, field))
 118     }
 119
 120     pub(crate) fn add_user_type(&self, user_ty: &PatternTypeProjection<'tcx>, sp: Span) -> Self {
 121         let mut new = self.clone();
 122         new.contents.push((user_ty.clone(), sp));
 123         new
 124     }
 125 }
 126
 127 #[derive(Clone, Debug)]
 128 pub struct PatternTypeProjection<'tcx>(UserTypeProjection<'tcx>);
 129
 130 impl<'tcx> PatternTypeProjection<'tcx> {
 131     pub(crate) fn index(&self) -> Self {
 132         let mut new = self.clone();
 133         new.0.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.0.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.0.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.0.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.0.projs.push(ProjectionElem::Downcast(adt_def, variant_index));
 161         new.0.projs.push(ProjectionElem::Field(field, ()));
 162         new
 163     }
 164
 165     pub(crate) fn from_canonical_ty(c_ty: ty::CanonicalTy<'tcx>) -> Self {
 166         Self::from_user_type(UserTypeAnnotation::Ty(c_ty))
 167     }
 168
 169     pub(crate) fn from_user_type(u_ty: UserTypeAnnotation<'tcx>) -> Self {
 170         Self::from_user_type_proj(UserTypeProjection { base: u_ty, projs: vec![], })
 171     }
 172
 173     pub(crate) fn from_user_type_proj(u_ty: UserTypeProjection<'tcx>) -> Self {
 174         PatternTypeProjection(u_ty)
 175     }
 176
 177     pub(crate) fn user_ty(self) -> UserTypeProjection<'tcx> { self.0 }
 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.name)?;
 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             let subpattern = Pattern {
 802                 span,
 803                 ty,
 804                 kind: Box::new(kind),
 805             };
 806
 807             debug!("pattern user_ty = {:?} for pattern at {:?}", user_ty, span);
 808
 809             let pat_ty = PatternTypeProjection::from_user_type(user_ty);
 810             kind = PatternKind::AscribeUserType {
 811                 subpattern,
 812                 user_ty: pat_ty,
 813                 user_ty_span: span,
 814             };
 815         }
 816
 817         kind
 818     }
 819
 820     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 821     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 822     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 823     fn lower_path(&mut self,
 824                   qpath: &hir::QPath,
 825                   id: hir::HirId,
 826                   span: Span)
 827                   -> Pattern<'tcx> {
 828         let ty = self.tables.node_id_to_type(id);
 829         let def = self.tables.qpath_def(qpath, id);
 830         let is_associated_const = match def {
 831             Def::AssociatedConst(_) => true,
 832             _ => false,
 833         };
 834         let kind = match def {
 835             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 836                 let substs = self.tables.node_substs(id);
 837                 match ty::Instance::resolve(
 838                     self.tcx,
 839                     self.param_env,
 840                     def_id,
 841                     substs,
 842                 ) {
 843                     Some(instance) => {
 844                         let cid = GlobalId {
 845                             instance,
 846                             promoted: None,
 847                         };
 848                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 849                             Ok(value) => {
 850                                 return self.const_to_pat(instance, value, id, span)
 851                             },
 852                             Err(_) => {
 853                                 self.tcx.sess.span_err(
 854                                     span,
 855                                     "could not evaluate constant pattern",
 856                                 );
 857                                 PatternKind::Wild
 858                             }
 859                         }
 860                     },
 861                     None => {
 862                         self.errors.push(if is_associated_const {
 863                             PatternError::AssociatedConstInPattern(span)
 864                         } else {
 865                             PatternError::StaticInPattern(span)
 866                         });
 867                         PatternKind::Wild
 868                     },
 869                 }
 870             }
 871             _ => self.lower_variant_or_leaf(def, id, span, ty, vec![]),
 872         };
 873
 874         Pattern {
 875             span,
 876             ty,
 877             kind: Box::new(kind),
 878         }
 879     }
 880
 881     /// Converts literals, paths and negation of literals to patterns.
 882     /// The special case for negation exists to allow things like -128i8
 883     /// which would overflow if we tried to evaluate 128i8 and then negate
 884     /// afterwards.
 885     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 886         match expr.node {
 887             hir::ExprKind::Lit(ref lit) => {
 888                 let ty = self.tables.expr_ty(expr);
 889                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 890                     Ok(val) => {
 891                         let instance = ty::Instance::new(
 892                             self.tables.local_id_root.expect("literal outside any scope"),
 893                             self.substs,
 894                         );
 895                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 896                     },
 897                     Err(LitToConstError::UnparseableFloat) => {
 898                         self.errors.push(PatternError::FloatBug);
 899                         PatternKind::Wild
 900                     },
 901                     Err(LitToConstError::Reported) => PatternKind::Wild,
 902                 }
 903             },
 904             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 905             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 906                 let ty = self.tables.expr_ty(expr);
 907                 let lit = match expr.node {
 908                     hir::ExprKind::Lit(ref lit) => lit,
 909                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 910                 };
 911                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 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             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 927         }
 928     }
 929
 930     /// Converts an evaluated constant to a pattern (if possible).
 931     /// This means aggregate values (like structs and enums) are converted
 932     /// to a pattern that matches the value (as if you'd compare via eq).
 933     fn const_to_pat(
 934         &self,
 935         instance: ty::Instance<'tcx>,
 936         cv: &'tcx ty::Const<'tcx>,
 937         id: hir::HirId,
 938         span: Span,
 939     ) -> Pattern<'tcx> {
 940         debug!("const_to_pat: cv={:#?}", cv);
 941         let adt_subpattern = |i, variant_opt| {
 942             let field = Field::new(i);
 943             let val = const_field(
 944                 self.tcx, self.param_env, instance,
 945                 variant_opt, field, cv,
 946             ).expect("field access failed");
 947             self.const_to_pat(instance, val, id, span)
 948         };
 949         let adt_subpatterns = |n, variant_opt| {
 950             (0..n).map(|i| {
 951                 let field = Field::new(i);
 952                 FieldPattern {
 953                     field,
 954                     pattern: adt_subpattern(i, variant_opt),
 955                 }
 956             }).collect::<Vec<_>>()
 957         };
 958         let kind = match cv.ty.sty {
 959             ty::Float(_) => {
 960                 let id = self.tcx.hir().hir_to_node_id(id);
 961                 self.tcx.lint_node(
 962                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 963                     id,
 964                     span,
 965                     "floating-point types cannot be used in patterns",
 966                 );
 967                 PatternKind::Constant {
 968                     value: cv,
 969                 }
 970             },
 971             ty::Adt(adt_def, _) if adt_def.is_union() => {
 972                 // Matching on union fields is unsafe, we can't hide it in constants
 973                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 974                 PatternKind::Wild
 975             }
 976             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 977                 let msg = format!("to use a constant of type `{}` in a pattern, \
 978                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 979                                     self.tcx.item_path_str(adt_def.did),
 980                                     self.tcx.item_path_str(adt_def.did));
 981                 self.tcx.sess.span_err(span, &msg);
 982                 PatternKind::Wild
 983             },
 984             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 985                 let variant_index = const_variant_index(
 986                     self.tcx, self.param_env, instance, cv
 987                 ).expect("const_variant_index failed");
 988                 let subpatterns = adt_subpatterns(
 989                     adt_def.variants[variant_index].fields.len(),
 990                     Some(variant_index),
 991                 );
 992                 PatternKind::Variant {
 993                     adt_def,
 994                     substs,
 995                     variant_index,
 996                     subpatterns,
 997                 }
 998             },
 999             ty::Adt(adt_def, _) => {
1000                 let struct_var = adt_def.non_enum_variant();
1001                 PatternKind::Leaf {
1002                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
1003                 }
1004             }
1005             ty::Tuple(fields) => {
1006                 PatternKind::Leaf {
1007                     subpatterns: adt_subpatterns(fields.len(), None),
1008                 }
1009             }
1010             ty::Array(_, n) => {
1011                 PatternKind::Array {
1012                     prefix: (0..n.unwrap_usize(self.tcx))
1013                         .map(|i| adt_subpattern(i as usize, None))
1014                         .collect(),
1015                     slice: None,
1016                     suffix: Vec::new(),
1017                 }
1018             }
1019             _ => {
1020                 PatternKind::Constant {
1021                     value: cv,
1022                 }
1023             },
1024         };
1025
1026         Pattern {
1027             span,
1028             ty: cv.ty,
1029             kind: Box::new(kind),
1030         }
1031     }
1032 }
1033
1034 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
1035     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
1036         self.tcx
1037     }
1038
1039     fn tables(&self) -> &ty::TypeckTables<'tcx> {
1040         self.tables
1041     }
1042 }
1043
1044
1045 pub trait PatternFoldable<'tcx> : Sized {
1046     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1047         self.super_fold_with(folder)
1048     }
1049
1050     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
1051 }
1052
1053 pub trait PatternFolder<'tcx> : Sized {
1054     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
1055         pattern.super_fold_with(self)
1056     }
1057
1058     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
1059         kind.super_fold_with(self)
1060     }
1061 }
1062
1063
1064 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
1065     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1066         let content: T = (**self).fold_with(folder);
1067         box content
1068     }
1069 }
1070
1071 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1072     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1073         self.iter().map(|t| t.fold_with(folder)).collect()
1074     }
1075 }
1076
1077 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1078     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1079         self.as_ref().map(|t| t.fold_with(folder))
1080     }
1081 }
1082
1083 macro_rules! CloneImpls {
1084     (<$lt_tcx:tt> $($ty:ty),+) => {
1085         $(
1086             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1087                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1088                     Clone::clone(self)
1089                 }
1090             }
1091         )+
1092     }
1093 }
1094
1095 CloneImpls!{ <'tcx>
1096     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
1097     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
1098     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, UserTypeAnnotation<'tcx>,
1099     UserTypeProjection<'tcx>, PatternTypeProjection<'tcx>
1100 }
1101
1102 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1103     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1104         FieldPattern {
1105             field: self.field.fold_with(folder),
1106             pattern: self.pattern.fold_with(folder)
1107         }
1108     }
1109 }
1110
1111 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1112     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1113         folder.fold_pattern(self)
1114     }
1115
1116     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1117         Pattern {
1118             ty: self.ty.fold_with(folder),
1119             span: self.span.fold_with(folder),
1120             kind: self.kind.fold_with(folder)
1121         }
1122     }
1123 }
1124
1125 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1126     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1127         folder.fold_pattern_kind(self)
1128     }
1129
1130     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1131         match *self {
1132             PatternKind::Wild => PatternKind::Wild,
1133             PatternKind::AscribeUserType {
1134                 ref subpattern,
1135                 ref user_ty,
1136                 user_ty_span,
1137             } => PatternKind::AscribeUserType {
1138                 subpattern: subpattern.fold_with(folder),
1139                 user_ty: user_ty.fold_with(folder),
1140                 user_ty_span,
1141             },
1142             PatternKind::Binding {
1143                 mutability,
1144                 name,
1145                 mode,
1146                 var,
1147                 ty,
1148                 ref subpattern,
1149             } => PatternKind::Binding {
1150                 mutability: mutability.fold_with(folder),
1151                 name: name.fold_with(folder),
1152                 mode: mode.fold_with(folder),
1153                 var: var.fold_with(folder),
1154                 ty: ty.fold_with(folder),
1155                 subpattern: subpattern.fold_with(folder),
1156             },
1157             PatternKind::Variant {
1158                 adt_def,
1159                 substs,
1160                 variant_index,
1161                 ref subpatterns,
1162             } => PatternKind::Variant {
1163                 adt_def: adt_def.fold_with(folder),
1164                 substs: substs.fold_with(folder),
1165                 variant_index,
1166                 subpatterns: subpatterns.fold_with(folder)
1167             },
1168             PatternKind::Leaf {
1169                 ref subpatterns,
1170             } => PatternKind::Leaf {
1171                 subpatterns: subpatterns.fold_with(folder),
1172             },
1173             PatternKind::Deref {
1174                 ref subpattern,
1175             } => PatternKind::Deref {
1176                 subpattern: subpattern.fold_with(folder),
1177             },
1178             PatternKind::Constant {
1179                 value
1180             } => PatternKind::Constant {
1181                 value: value.fold_with(folder)
1182             },
1183             PatternKind::Range(PatternRange {
1184                 lo,
1185                 hi,
1186                 ty,
1187                 end,
1188             }) => PatternKind::Range(PatternRange {
1189                 lo: lo.fold_with(folder),
1190                 hi: hi.fold_with(folder),
1191                 ty: ty.fold_with(folder),
1192                 end,
1193             }),
1194             PatternKind::Slice {
1195                 ref prefix,
1196                 ref slice,
1197                 ref suffix,
1198             } => PatternKind::Slice {
1199                 prefix: prefix.fold_with(folder),
1200                 slice: slice.fold_with(folder),
1201                 suffix: suffix.fold_with(folder)
1202             },
1203             PatternKind::Array {
1204                 ref prefix,
1205                 ref slice,
1206                 ref suffix
1207             } => PatternKind::Array {
1208                 prefix: prefix.fold_with(folder),
1209                 slice: slice.fold_with(folder),
1210                 suffix: suffix.fold_with(folder)
1211             },
1212         }
1213     }
1214 }
1215
1216 pub fn compare_const_vals<'a, 'gcx, 'tcx>(
1217     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1218     a: &'tcx ty::Const<'tcx>,
1219     b: &'tcx ty::Const<'tcx>,
1220     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1221 ) -> Option<Ordering> {
1222     trace!("compare_const_vals: {:?}, {:?}", a, b);
1223
1224     let from_bool = |v: bool| {
1225         if v {
1226             Some(Ordering::Equal)
1227         } else {
1228             None
1229         }
1230     };
1231
1232     let fallback = || from_bool(a == b);
1233
1234     // Use the fallback if any type differs
1235     if a.ty != b.ty || a.ty != ty.value {
1236         return fallback();
1237     }
1238
1239     let tcx = tcx.global_tcx();
1240     let (a, b, ty) = (a, b, ty).lift_to_tcx(tcx).unwrap();
1241
1242     // FIXME: This should use assert_bits(ty) instead of use_bits
1243     // but triggers possibly bugs due to mismatching of arrays and slices
1244     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1245         use ::rustc_apfloat::Float;
1246         return match ty.value.sty {
1247             ty::Float(ast::FloatTy::F32) => {
1248                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1249                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1250                 l.partial_cmp(&r)
1251             },
1252             ty::Float(ast::FloatTy::F64) => {
1253                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1254                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1255                 l.partial_cmp(&r)
1256             },
1257             ty::Int(_) => {
1258                 let layout = tcx.layout_of(ty).ok()?;
1259                 assert!(layout.abi.is_signed());
1260                 let a = sign_extend(a, layout.size);
1261                 let b = sign_extend(b, layout.size);
1262                 Some((a as i128).cmp(&(b as i128)))
1263             },
1264             _ => Some(a.cmp(&b)),
1265         }
1266     }
1267
1268     if let ty::Str = ty.value.sty {
1269         match (a.val, b.val) {
1270             (
1271                 ConstValue::ScalarPair(
1272                     Scalar::Ptr(ptr_a),
1273                     len_a,
1274                 ),
1275                 ConstValue::ScalarPair(
1276                     Scalar::Ptr(ptr_b),
1277                     len_b,
1278                 ),
1279             ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1280                 if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1281                     if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1282                         if len_a == len_b {
1283                             let map = tcx.alloc_map.lock();
1284                             let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1285                             let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1286                             if alloc_a.bytes.len() as u128 == len_a {
1287                                 return from_bool(alloc_a == alloc_b);
1288                             }
1289                         }
1290                     }
1291                 }
1292             }
1293             _ => (),
1294         }
1295     }
1296
1297     fallback()
1298 }