src/librustc_mir/hair/pattern/mod.rs

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