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 interpret::{const_field, const_variant_index};
  20
  21 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability};
  22 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  23 use rustc::ty::{self, CanonicalTy, TyCtxt, AdtDef, Ty, Region};
  24 use rustc::ty::subst::{Substs, Kind};
  25 use rustc::hir::{self, PatKind, RangeEnd};
  26 use rustc::hir::def::{Def, CtorKind};
  27 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  28
  29 use rustc_data_structures::indexed_vec::Idx;
  30
  31 use std::cmp::Ordering;
  32 use std::fmt;
  33 use syntax::ast;
  34 use syntax::ptr::P;
  35 use syntax_pos::Span;
  36 use syntax_pos::symbol::Symbol;
  37
  38 #[derive(Clone, Debug)]
  39 pub enum PatternError {
  40     AssociatedConstInPattern(Span),
  41     StaticInPattern(Span),
  42     FloatBug,
  43     NonConstPath(Span),
  44 }
  45
  46 #[derive(Copy, Clone, Debug)]
  47 pub enum BindingMode<'tcx> {
  48     ByValue,
  49     ByRef(Region<'tcx>, BorrowKind),
  50 }
  51
  52 #[derive(Clone, Debug)]
  53 pub struct FieldPattern<'tcx> {
  54     pub field: Field,
  55     pub pattern: Pattern<'tcx>,
  56 }
  57
  58 #[derive(Clone, Debug)]
  59 pub struct Pattern<'tcx> {
  60     pub ty: Ty<'tcx>,
  61     pub span: Span,
  62     pub kind: Box<PatternKind<'tcx>>,
  63 }
  64
  65 #[derive(Clone, Debug)]
  66 pub enum PatternKind<'tcx> {
  67     Wild,
  68
  69     AscribeUserType {
  70         user_ty: CanonicalTy<'tcx>,
  71         subpattern: Pattern<'tcx>,
  72     },
  73
  74     /// x, ref x, x @ P, etc
  75     Binding {
  76         mutability: Mutability,
  77         name: ast::Name,
  78         mode: BindingMode<'tcx>,
  79         var: ast::NodeId,
  80         ty: Ty<'tcx>,
  81         subpattern: Option<Pattern<'tcx>>,
  82     },
  83
  84     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
  85     Variant {
  86         adt_def: &'tcx AdtDef,
  87         substs: &'tcx Substs<'tcx>,
  88         variant_index: usize,
  89         subpatterns: Vec<FieldPattern<'tcx>>,
  90     },
  91
  92     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
  93     Leaf {
  94         subpatterns: Vec<FieldPattern<'tcx>>,
  95     },
  96
  97     /// box P, &P, &mut P, etc
  98     Deref {
  99         subpattern: Pattern<'tcx>,
 100     },
 101
 102     Constant {
 103         value: &'tcx ty::Const<'tcx>,
 104     },
 105
 106     Range {
 107         lo: &'tcx ty::Const<'tcx>,
 108         hi: &'tcx ty::Const<'tcx>,
 109         ty: Ty<'tcx>,
 110         end: RangeEnd,
 111     },
 112
 113     /// matches against a slice, checking the length and extracting elements.
 114     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 115     /// e.g. `&[ref xs..]`.
 116     Slice {
 117         prefix: Vec<Pattern<'tcx>>,
 118         slice: Option<Pattern<'tcx>>,
 119         suffix: Vec<Pattern<'tcx>>,
 120     },
 121
 122     /// fixed match against an array, irrefutable
 123     Array {
 124         prefix: Vec<Pattern<'tcx>>,
 125         slice: Option<Pattern<'tcx>>,
 126         suffix: Vec<Pattern<'tcx>>,
 127     },
 128 }
 129
 130 impl<'tcx> fmt::Display for Pattern<'tcx> {
 131     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 132         match *self.kind {
 133             PatternKind::Wild => write!(f, "_"),
 134             PatternKind::AscribeUserType { ref subpattern, .. } =>
 135                 write!(f, "{}: _", subpattern),
 136             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 137                 let is_mut = match mode {
 138                     BindingMode::ByValue => mutability == Mutability::Mut,
 139                     BindingMode::ByRef(_, bk) => {
 140                         write!(f, "ref ")?;
 141                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 142                     }
 143                 };
 144                 if is_mut {
 145                     write!(f, "mut ")?;
 146                 }
 147                 write!(f, "{}", name)?;
 148                 if let Some(ref subpattern) = *subpattern {
 149                     write!(f, " @ {}", subpattern)?;
 150                 }
 151                 Ok(())
 152             }
 153             PatternKind::Variant { ref subpatterns, .. } |
 154             PatternKind::Leaf { ref subpatterns } => {
 155                 let variant = match *self.kind {
 156                     PatternKind::Variant { adt_def, variant_index, .. } => {
 157                         Some(&adt_def.variants[variant_index])
 158                     }
 159                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 160                         if !adt.is_enum() {
 161                             Some(&adt.variants[0])
 162                         } else {
 163                             None
 164                         }
 165                     } else {
 166                         None
 167                     }
 168                 };
 169
 170                 let mut first = true;
 171                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 172
 173                 if let Some(variant) = variant {
 174                     write!(f, "{}", variant.name)?;
 175
 176                     // Only for Adt we can have `S {...}`,
 177                     // which we handle separately here.
 178                     if variant.ctor_kind == CtorKind::Fictive {
 179                         write!(f, " {{ ")?;
 180
 181                         let mut printed = 0;
 182                         for p in subpatterns {
 183                             if let PatternKind::Wild = *p.pattern.kind {
 184                                 continue;
 185                             }
 186                             let name = variant.fields[p.field.index()].ident;
 187                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 188                             printed += 1;
 189                         }
 190
 191                         if printed < variant.fields.len() {
 192                             write!(f, "{}..", start_or_continue())?;
 193                         }
 194
 195                         return write!(f, " }}");
 196                     }
 197                 }
 198
 199                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 200                 if num_fields != 0 || variant.is_none() {
 201                     write!(f, "(")?;
 202                     for i in 0..num_fields {
 203                         write!(f, "{}", start_or_continue())?;
 204
 205                         // Common case: the field is where we expect it.
 206                         if let Some(p) = subpatterns.get(i) {
 207                             if p.field.index() == i {
 208                                 write!(f, "{}", p.pattern)?;
 209                                 continue;
 210                             }
 211                         }
 212
 213                         // Otherwise, we have to go looking for it.
 214                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 215                             write!(f, "{}", p.pattern)?;
 216                         } else {
 217                             write!(f, "_")?;
 218                         }
 219                     }
 220                     write!(f, ")")?;
 221                 }
 222
 223                 Ok(())
 224             }
 225             PatternKind::Deref { ref subpattern } => {
 226                 match self.ty.sty {
 227                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 228                     ty::Ref(_, _, mutbl) => {
 229                         write!(f, "&")?;
 230                         if mutbl == hir::MutMutable {
 231                             write!(f, "mut ")?;
 232                         }
 233                     }
 234                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 235                 }
 236                 write!(f, "{}", subpattern)
 237             }
 238             PatternKind::Constant { value } => {
 239                 fmt_const_val(f, value)
 240             }
 241             PatternKind::Range { lo, hi, ty: _, end } => {
 242                 fmt_const_val(f, lo)?;
 243                 match end {
 244                     RangeEnd::Included => write!(f, "..=")?,
 245                     RangeEnd::Excluded => write!(f, "..")?,
 246                 }
 247                 fmt_const_val(f, hi)
 248             }
 249             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 250             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 251                 let mut first = true;
 252                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 253                 write!(f, "[")?;
 254                 for p in prefix {
 255                     write!(f, "{}{}", start_or_continue(), p)?;
 256                 }
 257                 if let Some(ref slice) = *slice {
 258                     write!(f, "{}", start_or_continue())?;
 259                     match *slice.kind {
 260                         PatternKind::Wild => {}
 261                         _ => write!(f, "{}", slice)?
 262                     }
 263                     write!(f, "..")?;
 264                 }
 265                 for p in suffix {
 266                     write!(f, "{}{}", start_or_continue(), p)?;
 267                 }
 268                 write!(f, "]")
 269             }
 270         }
 271     }
 272 }
 273
 274 pub struct PatternContext<'a, 'tcx: 'a> {
 275     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 276     pub param_env: ty::ParamEnv<'tcx>,
 277     pub tables: &'a ty::TypeckTables<'tcx>,
 278     pub substs: &'tcx Substs<'tcx>,
 279     pub errors: Vec<PatternError>,
 280 }
 281
 282 impl<'a, 'tcx> Pattern<'tcx> {
 283     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 284                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 285                     tables: &'a ty::TypeckTables<'tcx>,
 286                     pat: &'tcx hir::Pat) -> Self {
 287         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 288         let result = pcx.lower_pattern(pat);
 289         if !pcx.errors.is_empty() {
 290             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 291             tcx.sess.delay_span_bug(pat.span, &msg);
 292         }
 293         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 294         result
 295     }
 296 }
 297
 298 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 299     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 300                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 301                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 302         PatternContext {
 303             tcx,
 304             param_env: param_env_and_substs.param_env,
 305             tables,
 306             substs: param_env_and_substs.value,
 307             errors: vec![]
 308         }
 309     }
 310
 311     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 312         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 313         // pattern has the type that results *after* dereferencing. For example, in this code:
 314         //
 315         // ```
 316         // match &&Some(0i32) {
 317         //     Some(n) => { ... },
 318         //     _ => { ... },
 319         // }
 320         // ```
 321         //
 322         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 323         // determined in rustc_typeck::check::match). The adjustments would be
 324         //
 325         // `vec![&&Option<i32>, &Option<i32>]`.
 326         //
 327         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 328         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 329         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 330         // gets the least-dereferenced type).
 331         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 332         self.tables
 333             .pat_adjustments()
 334             .get(pat.hir_id)
 335             .unwrap_or(&vec![])
 336             .iter()
 337             .rev()
 338             .fold(unadjusted_pat, |pat, ref_ty| {
 339                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 340                     Pattern {
 341                         span: pat.span,
 342                         ty: ref_ty,
 343                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 344                     }
 345                 },
 346             )
 347     }
 348
 349     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 350         let mut ty = self.tables.node_id_to_type(pat.hir_id);
 351
 352         let kind = match pat.node {
 353             PatKind::Wild => PatternKind::Wild,
 354
 355             PatKind::Lit(ref value) => self.lower_lit(value),
 356
 357             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 358                 match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
 359                     (PatternKind::Constant { value: lo },
 360                      PatternKind::Constant { value: hi }) => {
 361                         use std::cmp::Ordering;
 362                         let cmp = compare_const_vals(
 363                             self.tcx,
 364                             lo,
 365                             hi,
 366                             self.param_env.and(ty),
 367                         );
 368                         match (end, cmp) {
 369                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 370                                 PatternKind::Range { lo, hi, ty, end },
 371                             (RangeEnd::Excluded, _) => {
 372                                 span_err!(
 373                                     self.tcx.sess,
 374                                     lo_expr.span,
 375                                     E0579,
 376                                     "lower range bound must be less than upper",
 377                                 );
 378                                 PatternKind::Wild
 379                             }
 380                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 381                                 PatternKind::Constant { value: lo }
 382                             }
 383                             (RangeEnd::Included, Some(Ordering::Less)) => {
 384                                 PatternKind::Range { lo, hi, ty, end }
 385                             }
 386                             (RangeEnd::Included, _) => {
 387                                 let mut err = struct_span_err!(
 388                                     self.tcx.sess,
 389                                     lo_expr.span,
 390                                     E0030,
 391                                     "lower range bound must be less than or equal to upper"
 392                                 );
 393                                 err.span_label(
 394                                     lo_expr.span,
 395                                     "lower bound larger than upper bound",
 396                                 );
 397                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 398                                     err.note("When matching against a range, the compiler \
 399                                               verifies that the range is non-empty. Range \
 400                                               patterns include both end-points, so this is \
 401                                               equivalent to requiring the start of the range \
 402                                               to be less than or equal to the end of the range.");
 403                                 }
 404                                 err.emit();
 405                                 PatternKind::Wild
 406                             }
 407                         }
 408                     }
 409                     _ => PatternKind::Wild
 410                 }
 411             }
 412
 413             PatKind::Path(ref qpath) => {
 414                 return self.lower_path(qpath, pat.hir_id, pat.span);
 415             }
 416
 417             PatKind::Ref(ref subpattern, _) |
 418             PatKind::Box(ref subpattern) => {
 419                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 420             }
 421
 422             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 423                 match ty.sty {
 424                     ty::Ref(_, ty, _) =>
 425                         PatternKind::Deref {
 426                             subpattern: Pattern {
 427                                 ty,
 428                                 span: pat.span,
 429                                 kind: Box::new(self.slice_or_array_pattern(
 430                                     pat.span, ty, prefix, slice, suffix))
 431                             },
 432                         },
 433                     ty::Slice(..) |
 434                     ty::Array(..) =>
 435                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 436                     ty::Error => { // Avoid ICE
 437                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 438                     }
 439                     ref sty =>
 440                         span_bug!(
 441                             pat.span,
 442                             "unexpanded type for vector pattern: {:?}",
 443                             sty),
 444                 }
 445             }
 446
 447             PatKind::Tuple(ref subpatterns, ddpos) => {
 448                 match ty.sty {
 449                     ty::Tuple(ref tys) => {
 450                         let subpatterns =
 451                             subpatterns.iter()
 452                                        .enumerate_and_adjust(tys.len(), ddpos)
 453                                        .map(|(i, subpattern)| FieldPattern {
 454                                             field: Field::new(i),
 455                                             pattern: self.lower_pattern(subpattern)
 456                                        })
 457                                        .collect();
 458
 459                         PatternKind::Leaf { subpatterns: subpatterns }
 460                     }
 461                     ty::Error => { // Avoid ICE (#50577)
 462                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 463                     }
 464                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 465                 }
 466             }
 467
 468             PatKind::Binding(_, id, ident, ref sub) => {
 469                 let var_ty = self.tables.node_id_to_type(pat.hir_id);
 470                 let region = match var_ty.sty {
 471                     ty::Ref(r, _, _) => Some(r),
 472                     ty::Error => { // Avoid ICE
 473                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 474                     }
 475                     _ => None,
 476                 };
 477                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 478                                                          .expect("missing binding mode");
 479                 let (mutability, mode) = match bm {
 480                     ty::BindByValue(hir::MutMutable) =>
 481                         (Mutability::Mut, BindingMode::ByValue),
 482                     ty::BindByValue(hir::MutImmutable) =>
 483                         (Mutability::Not, BindingMode::ByValue),
 484                     ty::BindByReference(hir::MutMutable) =>
 485                         (Mutability::Not, BindingMode::ByRef(
 486                             region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
 487                     ty::BindByReference(hir::MutImmutable) =>
 488                         (Mutability::Not, BindingMode::ByRef(
 489                             region.unwrap(), BorrowKind::Shared)),
 490                 };
 491
 492                 // A ref x pattern is the same node used for x, and as such it has
 493                 // x's type, which is &T, where we want T (the type being matched).
 494                 if let ty::BindByReference(_) = bm {
 495                     if let ty::Ref(_, rty, _) = ty.sty {
 496                         ty = rty;
 497                     } else {
 498                         bug!("`ref {}` has wrong type {}", ident, ty);
 499                     }
 500                 }
 501
 502                 PatternKind::Binding {
 503                     mutability,
 504                     mode,
 505                     name: ident.name,
 506                     var: id,
 507                     ty: var_ty,
 508                     subpattern: self.lower_opt_pattern(sub),
 509                 }
 510             }
 511
 512             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 513                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 514                 let adt_def = match ty.sty {
 515                     ty::Adt(adt_def, _) => adt_def,
 516                     ty::Error => { // Avoid ICE (#50585)
 517                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 518                     }
 519                     _ => span_bug!(pat.span,
 520                                    "tuple struct pattern not applied to an ADT {:?}",
 521                                    ty.sty),
 522                 };
 523                 let variant_def = adt_def.variant_of_def(def);
 524
 525                 let subpatterns =
 526                         subpatterns.iter()
 527                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 528                                    .map(|(i, field)| FieldPattern {
 529                                        field: Field::new(i),
 530                                        pattern: self.lower_pattern(field),
 531                                    })
 532                                    .collect();
 533                 self.lower_variant_or_leaf(def, pat.span, ty, subpatterns)
 534             }
 535
 536             PatKind::Struct(ref qpath, ref fields, _) => {
 537                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 538                 let subpatterns =
 539                     fields.iter()
 540                           .map(|field| {
 541                               FieldPattern {
 542                                   field: Field::new(self.tcx.field_index(field.node.id,
 543                                                                          self.tables)),
 544                                   pattern: self.lower_pattern(&field.node.pat),
 545                               }
 546                           })
 547                           .collect();
 548
 549                 self.lower_variant_or_leaf(def, pat.span, ty, subpatterns)
 550             }
 551         };
 552
 553         Pattern {
 554             span: pat.span,
 555             ty,
 556             kind: Box::new(kind),
 557         }
 558     }
 559
 560     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 561         pats.iter().map(|p| self.lower_pattern(p)).collect()
 562     }
 563
 564     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 565     {
 566         pat.as_ref().map(|p| self.lower_pattern(p))
 567     }
 568
 569     fn flatten_nested_slice_patterns(
 570         &mut self,
 571         prefix: Vec<Pattern<'tcx>>,
 572         slice: Option<Pattern<'tcx>>,
 573         suffix: Vec<Pattern<'tcx>>)
 574         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 575     {
 576         let orig_slice = match slice {
 577             Some(orig_slice) => orig_slice,
 578             None => return (prefix, slice, suffix)
 579         };
 580         let orig_prefix = prefix;
 581         let orig_suffix = suffix;
 582
 583         // dance because of intentional borrow-checker stupidity.
 584         let kind = *orig_slice.kind;
 585         match kind {
 586             PatternKind::Slice { prefix, slice, mut suffix } |
 587             PatternKind::Array { prefix, slice, mut suffix } => {
 588                 let mut orig_prefix = orig_prefix;
 589
 590                 orig_prefix.extend(prefix);
 591                 suffix.extend(orig_suffix);
 592
 593                 (orig_prefix, slice, suffix)
 594             }
 595             _ => {
 596                 (orig_prefix, Some(Pattern {
 597                     kind: box kind, ..orig_slice
 598                 }), orig_suffix)
 599             }
 600         }
 601     }
 602
 603     fn slice_or_array_pattern(
 604         &mut self,
 605         span: Span,
 606         ty: Ty<'tcx>,
 607         prefix: &'tcx [P<hir::Pat>],
 608         slice: &'tcx Option<P<hir::Pat>>,
 609         suffix: &'tcx [P<hir::Pat>])
 610         -> PatternKind<'tcx>
 611     {
 612         let prefix = self.lower_patterns(prefix);
 613         let slice = self.lower_opt_pattern(slice);
 614         let suffix = self.lower_patterns(suffix);
 615         let (prefix, slice, suffix) =
 616             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 617
 618         match ty.sty {
 619             ty::Slice(..) => {
 620                 // matching a slice or fixed-length array
 621                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 622             }
 623
 624             ty::Array(_, len) => {
 625                 // fixed-length array
 626                 let len = len.unwrap_usize(self.tcx);
 627                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 628                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 629             }
 630
 631             _ => {
 632                 span_bug!(span, "bad slice pattern type {:?}", ty);
 633             }
 634         }
 635     }
 636
 637     fn lower_variant_or_leaf(
 638         &mut self,
 639         def: Def,
 640         span: Span,
 641         ty: Ty<'tcx>,
 642         subpatterns: Vec<FieldPattern<'tcx>>)
 643         -> PatternKind<'tcx>
 644     {
 645         match def {
 646             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 647                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 648                 let adt_def = self.tcx.adt_def(enum_id);
 649                 if adt_def.is_enum() {
 650                     let substs = match ty.sty {
 651                         ty::Adt(_, substs) |
 652                         ty::FnDef(_, substs) => substs,
 653                         ty::Error => {  // Avoid ICE (#50585)
 654                             return PatternKind::Wild;
 655                         }
 656                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 657                     };
 658                     PatternKind::Variant {
 659                         adt_def,
 660                         substs,
 661                         variant_index: adt_def.variant_index_with_id(variant_id),
 662                         subpatterns,
 663                     }
 664                 } else {
 665                     PatternKind::Leaf { subpatterns: subpatterns }
 666                 }
 667             }
 668
 669             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 670             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 671                 PatternKind::Leaf { subpatterns: subpatterns }
 672             }
 673
 674             _ => {
 675                 self.errors.push(PatternError::NonConstPath(span));
 676                 PatternKind::Wild
 677             }
 678         }
 679     }
 680
 681     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 682     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 683     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 684     fn lower_path(&mut self,
 685                   qpath: &hir::QPath,
 686                   id: hir::HirId,
 687                   span: Span)
 688                   -> Pattern<'tcx> {
 689         let ty = self.tables.node_id_to_type(id);
 690         let def = self.tables.qpath_def(qpath, id);
 691         let is_associated_const = match def {
 692             Def::AssociatedConst(_) => true,
 693             _ => false,
 694         };
 695         let kind = match def {
 696             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 697                 let substs = self.tables.node_substs(id);
 698                 match ty::Instance::resolve(
 699                     self.tcx,
 700                     self.param_env,
 701                     def_id,
 702                     substs,
 703                 ) {
 704                     Some(instance) => {
 705                         let cid = GlobalId {
 706                             instance,
 707                             promoted: None,
 708                         };
 709                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 710                             Ok(value) => {
 711                                 return self.const_to_pat(instance, value, id, span)
 712                             },
 713                             Err(err) => {
 714                                 err.report_as_error(
 715                                     self.tcx.at(span),
 716                                     "could not evaluate constant pattern",
 717                                 );
 718                                 PatternKind::Wild
 719                             },
 720                         }
 721                     },
 722                     None => {
 723                         self.errors.push(if is_associated_const {
 724                             PatternError::AssociatedConstInPattern(span)
 725                         } else {
 726                             PatternError::StaticInPattern(span)
 727                         });
 728                         PatternKind::Wild
 729                     },
 730                 }
 731             }
 732             _ => self.lower_variant_or_leaf(def, span, ty, vec![]),
 733         };
 734
 735         Pattern {
 736             span,
 737             ty,
 738             kind: Box::new(kind),
 739         }
 740     }
 741
 742     /// Converts literals, paths and negation of literals to patterns.
 743     /// The special case for negation exists to allow things like -128i8
 744     /// which would overflow if we tried to evaluate 128i8 and then negate
 745     /// afterwards.
 746     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 747         match expr.node {
 748             hir::ExprKind::Lit(ref lit) => {
 749                 let ty = self.tables.expr_ty(expr);
 750                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 751                     Ok(val) => {
 752                         let instance = ty::Instance::new(
 753                             self.tables.local_id_root.expect("literal outside any scope"),
 754                             self.substs,
 755                         );
 756                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 757                     },
 758                     Err(e) => {
 759                         if e == LitToConstError::UnparseableFloat {
 760                             self.errors.push(PatternError::FloatBug);
 761                         }
 762                         PatternKind::Wild
 763                     },
 764                 }
 765             },
 766             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 767             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 768                 let ty = self.tables.expr_ty(expr);
 769                 let lit = match expr.node {
 770                     hir::ExprKind::Lit(ref lit) => lit,
 771                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 772                 };
 773                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 774                     Ok(val) => {
 775                         let instance = ty::Instance::new(
 776                             self.tables.local_id_root.expect("literal outside any scope"),
 777                             self.substs,
 778                         );
 779                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 780                     },
 781                     Err(e) => {
 782                         if e == LitToConstError::UnparseableFloat {
 783                             self.errors.push(PatternError::FloatBug);
 784                         }
 785                         PatternKind::Wild
 786                     },
 787                 }
 788             }
 789             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 790         }
 791     }
 792
 793     /// Converts an evaluated constant to a pattern (if possible).
 794     /// This means aggregate values (like structs and enums) are converted
 795     /// to a pattern that matches the value (as if you'd compare via eq).
 796     fn const_to_pat(
 797         &self,
 798         instance: ty::Instance<'tcx>,
 799         cv: &'tcx ty::Const<'tcx>,
 800         id: hir::HirId,
 801         span: Span,
 802     ) -> Pattern<'tcx> {
 803         debug!("const_to_pat: cv={:#?}", cv);
 804         let adt_subpattern = |i, variant_opt| {
 805             let field = Field::new(i);
 806             let val = const_field(
 807                 self.tcx, self.param_env, instance,
 808                 variant_opt, field, cv,
 809             ).expect("field access failed");
 810             self.const_to_pat(instance, val, id, span)
 811         };
 812         let adt_subpatterns = |n, variant_opt| {
 813             (0..n).map(|i| {
 814                 let field = Field::new(i);
 815                 FieldPattern {
 816                     field,
 817                     pattern: adt_subpattern(i, variant_opt),
 818                 }
 819             }).collect::<Vec<_>>()
 820         };
 821         let kind = match cv.ty.sty {
 822             ty::Float(_) => {
 823                 let id = self.tcx.hir.hir_to_node_id(id);
 824                 self.tcx.lint_node(
 825                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 826                     id,
 827                     span,
 828                     "floating-point types cannot be used in patterns",
 829                 );
 830                 PatternKind::Constant {
 831                     value: cv,
 832                 }
 833             },
 834             ty::Adt(adt_def, _) if adt_def.is_union() => {
 835                 // Matching on union fields is unsafe, we can't hide it in constants
 836                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 837                 PatternKind::Wild
 838             }
 839             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 840                 let msg = format!("to use a constant of type `{}` in a pattern, \
 841                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 842                                     self.tcx.item_path_str(adt_def.did),
 843                                     self.tcx.item_path_str(adt_def.did));
 844                 self.tcx.sess.span_err(span, &msg);
 845                 PatternKind::Wild
 846             },
 847             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 848                 let variant_index = const_variant_index(
 849                     self.tcx, self.param_env, instance, cv
 850                 ).expect("const_variant_index failed");
 851                 let subpatterns = adt_subpatterns(
 852                     adt_def.variants[variant_index].fields.len(),
 853                     Some(variant_index),
 854                 );
 855                 PatternKind::Variant {
 856                     adt_def,
 857                     substs,
 858                     variant_index,
 859                     subpatterns,
 860                 }
 861             },
 862             ty::Adt(adt_def, _) => {
 863                 let struct_var = adt_def.non_enum_variant();
 864                 PatternKind::Leaf {
 865                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
 866                 }
 867             }
 868             ty::Tuple(fields) => {
 869                 PatternKind::Leaf {
 870                     subpatterns: adt_subpatterns(fields.len(), None),
 871                 }
 872             }
 873             ty::Array(_, n) => {
 874                 PatternKind::Array {
 875                     prefix: (0..n.unwrap_usize(self.tcx))
 876                         .map(|i| adt_subpattern(i as usize, None))
 877                         .collect(),
 878                     slice: None,
 879                     suffix: Vec::new(),
 880                 }
 881             }
 882             _ => {
 883                 PatternKind::Constant {
 884                     value: cv,
 885                 }
 886             },
 887         };
 888
 889         Pattern {
 890             span,
 891             ty: cv.ty,
 892             kind: Box::new(kind),
 893         }
 894     }
 895 }
 896
 897 pub trait PatternFoldable<'tcx> : Sized {
 898     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 899         self.super_fold_with(folder)
 900     }
 901
 902     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
 903 }
 904
 905 pub trait PatternFolder<'tcx> : Sized {
 906     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
 907         pattern.super_fold_with(self)
 908     }
 909
 910     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
 911         kind.super_fold_with(self)
 912     }
 913 }
 914
 915
 916 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
 917     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 918         let content: T = (**self).fold_with(folder);
 919         box content
 920     }
 921 }
 922
 923 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
 924     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 925         self.iter().map(|t| t.fold_with(folder)).collect()
 926     }
 927 }
 928
 929 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
 930     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
 931         self.as_ref().map(|t| t.fold_with(folder))
 932     }
 933 }
 934
 935 macro_rules! CloneImpls {
 936     (<$lt_tcx:tt> $($ty:ty),+) => {
 937         $(
 938             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
 939                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
 940                     Clone::clone(self)
 941                 }
 942             }
 943         )+
 944     }
 945 }
 946
 947 CloneImpls!{ <'tcx>
 948     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
 949     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
 950     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, CanonicalTy<'tcx>
 951 }
 952
 953 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
 954     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 955         FieldPattern {
 956             field: self.field.fold_with(folder),
 957             pattern: self.pattern.fold_with(folder)
 958         }
 959     }
 960 }
 961
 962 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
 963     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 964         folder.fold_pattern(self)
 965     }
 966
 967     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 968         Pattern {
 969             ty: self.ty.fold_with(folder),
 970             span: self.span.fold_with(folder),
 971             kind: self.kind.fold_with(folder)
 972         }
 973     }
 974 }
 975
 976 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
 977     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 978         folder.fold_pattern_kind(self)
 979     }
 980
 981     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 982         match *self {
 983             PatternKind::Wild => PatternKind::Wild,
 984             PatternKind::AscribeUserType {
 985                 ref subpattern,
 986                 user_ty,
 987             } => PatternKind::AscribeUserType {
 988                 subpattern: subpattern.fold_with(folder),
 989                 user_ty: user_ty.fold_with(folder),
 990             },
 991             PatternKind::Binding {
 992                 mutability,
 993                 name,
 994                 mode,
 995                 var,
 996                 ty,
 997                 ref subpattern,
 998             } => PatternKind::Binding {
 999                 mutability: mutability.fold_with(folder),
1000                 name: name.fold_with(folder),
1001                 mode: mode.fold_with(folder),
1002                 var: var.fold_with(folder),
1003                 ty: ty.fold_with(folder),
1004                 subpattern: subpattern.fold_with(folder),
1005             },
1006             PatternKind::Variant {
1007                 adt_def,
1008                 substs,
1009                 variant_index,
1010                 ref subpatterns,
1011             } => PatternKind::Variant {
1012                 adt_def: adt_def.fold_with(folder),
1013                 substs: substs.fold_with(folder),
1014                 variant_index: variant_index.fold_with(folder),
1015                 subpatterns: subpatterns.fold_with(folder)
1016             },
1017             PatternKind::Leaf {
1018                 ref subpatterns,
1019             } => PatternKind::Leaf {
1020                 subpatterns: subpatterns.fold_with(folder),
1021             },
1022             PatternKind::Deref {
1023                 ref subpattern,
1024             } => PatternKind::Deref {
1025                 subpattern: subpattern.fold_with(folder),
1026             },
1027             PatternKind::Constant {
1028                 value
1029             } => PatternKind::Constant {
1030                 value: value.fold_with(folder)
1031             },
1032             PatternKind::Range {
1033                 lo,
1034                 hi,
1035                 ty,
1036                 end,
1037             } => PatternKind::Range {
1038                 lo: lo.fold_with(folder),
1039                 hi: hi.fold_with(folder),
1040                 ty: ty.fold_with(folder),
1041                 end,
1042             },
1043             PatternKind::Slice {
1044                 ref prefix,
1045                 ref slice,
1046                 ref suffix,
1047             } => PatternKind::Slice {
1048                 prefix: prefix.fold_with(folder),
1049                 slice: slice.fold_with(folder),
1050                 suffix: suffix.fold_with(folder)
1051             },
1052             PatternKind::Array {
1053                 ref prefix,
1054                 ref slice,
1055                 ref suffix
1056             } => PatternKind::Array {
1057                 prefix: prefix.fold_with(folder),
1058                 slice: slice.fold_with(folder),
1059                 suffix: suffix.fold_with(folder)
1060             },
1061         }
1062     }
1063 }
1064
1065 pub fn compare_const_vals<'a, 'tcx>(
1066     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1067     a: &'tcx ty::Const<'tcx>,
1068     b: &'tcx ty::Const<'tcx>,
1069     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1070 ) -> Option<Ordering> {
1071     trace!("compare_const_vals: {:?}, {:?}", a, b);
1072
1073     let from_bool = |v: bool| {
1074         if v {
1075             Some(Ordering::Equal)
1076         } else {
1077             None
1078         }
1079     };
1080
1081     let fallback = || from_bool(a == b);
1082
1083     // Use the fallback if any type differs
1084     if a.ty != b.ty || a.ty != ty.value {
1085         return fallback();
1086     }
1087
1088     // FIXME: This should use assert_bits(ty) instead of use_bits
1089     // but triggers possibly bugs due to mismatching of arrays and slices
1090     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1091         use ::rustc_apfloat::Float;
1092         return match ty.value.sty {
1093             ty::Float(ast::FloatTy::F32) => {
1094                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1095                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1096                 l.partial_cmp(&r)
1097             },
1098             ty::Float(ast::FloatTy::F64) => {
1099                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1100                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1101                 l.partial_cmp(&r)
1102             },
1103             ty::Int(_) => {
1104                 let layout = tcx.layout_of(ty).ok()?;
1105                 assert!(layout.abi.is_signed());
1106                 let a = sign_extend(a, layout.size);
1107                 let b = sign_extend(b, layout.size);
1108                 Some((a as i128).cmp(&(b as i128)))
1109             },
1110             _ => Some(a.cmp(&b)),
1111         }
1112     }
1113
1114     if let ty::Ref(_, rty, _) = ty.value.sty {
1115         if let ty::Str = rty.sty {
1116             match (a.val, b.val) {
1117                 (
1118                     ConstValue::ScalarPair(
1119                         Scalar::Ptr(ptr_a),
1120                         len_a,
1121                     ),
1122                     ConstValue::ScalarPair(
1123                         Scalar::Ptr(ptr_b),
1124                         len_b,
1125                     ),
1126                 ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1127                     let len_a = len_a.not_undef().ok();
1128                     let len_b = len_b.not_undef().ok();
1129                     if len_a.is_none() || len_b.is_none() {
1130                         tcx.sess.struct_err("str slice len is undef").delay_as_bug();
1131                     }
1132                     let len_a = len_a?;
1133                     let len_b = len_b?;
1134                     if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1135                         if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1136                             if len_a == len_b {
1137                                 let map = tcx.alloc_map.lock();
1138                                 let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1139                                 let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1140                                 if alloc_a.bytes.len() as u128 == len_a {
1141                                     return from_bool(alloc_a == alloc_b);
1142                                 }
1143                             }
1144                         }
1145                     }
1146                 }
1147                 _ => (),
1148             }
1149         }
1150     }
1151
1152     fallback()
1153 }
1154
1155 #[derive(PartialEq)]
1156 enum LitToConstError {
1157     UnparseableFloat,
1158     Propagated,
1159 }
1160
1161 // FIXME: Combine with rustc_mir::hair::cx::const_eval_literal
1162 fn lit_to_const<'a, 'tcx>(lit: &'tcx ast::LitKind,
1163                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
1164                           ty: Ty<'tcx>,
1165                           neg: bool)
1166                           -> Result<&'tcx ty::Const<'tcx>, LitToConstError> {
1167     use syntax::ast::*;
1168
1169     use rustc::mir::interpret::*;
1170     let lit = match *lit {
1171         LitKind::Str(ref s, _) => {
1172             let s = s.as_str();
1173             let id = tcx.allocate_bytes(s.as_bytes());
1174             ConstValue::new_slice(Scalar::Ptr(id.into()), s.len() as u64, tcx)
1175         },
1176         LitKind::ByteStr(ref data) => {
1177             let id = tcx.allocate_bytes(data);
1178             ConstValue::Scalar(Scalar::Ptr(id.into()))
1179         },
1180         LitKind::Byte(n) => ConstValue::Scalar(Scalar::Bits {
1181             bits: n as u128,
1182             size: 1,
1183         }),
1184         LitKind::Int(n, _) => {
1185             enum Int {
1186                 Signed(IntTy),
1187                 Unsigned(UintTy),
1188             }
1189             let ity = match ty.sty {
1190                 ty::Int(IntTy::Isize) => Int::Signed(tcx.sess.target.isize_ty),
1191                 ty::Int(other) => Int::Signed(other),
1192                 ty::Uint(UintTy::Usize) => Int::Unsigned(tcx.sess.target.usize_ty),
1193                 ty::Uint(other) => Int::Unsigned(other),
1194                 ty::Error => { // Avoid ICE (#51963)
1195                     return Err(LitToConstError::Propagated);
1196                 }
1197                 _ => bug!("literal integer type with bad type ({:?})", ty.sty),
1198             };
1199             // This converts from LitKind::Int (which is sign extended) to
1200             // Scalar::Bytes (which is zero extended)
1201             let n = match ity {
1202                 // FIXME(oli-obk): are these casts correct?
1203                 Int::Signed(IntTy::I8) if neg =>
1204                     (n as i8).overflowing_neg().0 as u8 as u128,
1205                 Int::Signed(IntTy::I16) if neg =>
1206                     (n as i16).overflowing_neg().0 as u16 as u128,
1207                 Int::Signed(IntTy::I32) if neg =>
1208                     (n as i32).overflowing_neg().0 as u32 as u128,
1209                 Int::Signed(IntTy::I64) if neg =>
1210                     (n as i64).overflowing_neg().0 as u64 as u128,
1211                 Int::Signed(IntTy::I128) if neg =>
1212                     (n as i128).overflowing_neg().0 as u128,
1213                 Int::Signed(IntTy::I8) | Int::Unsigned(UintTy::U8) => n as u8 as u128,
1214                 Int::Signed(IntTy::I16) | Int::Unsigned(UintTy::U16) => n as u16 as u128,
1215                 Int::Signed(IntTy::I32) | Int::Unsigned(UintTy::U32) => n as u32 as u128,
1216                 Int::Signed(IntTy::I64) | Int::Unsigned(UintTy::U64) => n as u64 as u128,
1217                 Int::Signed(IntTy::I128)| Int::Unsigned(UintTy::U128) => n,
1218                 _ => bug!(),
1219             };
1220             let size = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap().size.bytes() as u8;
1221             ConstValue::Scalar(Scalar::Bits {
1222                 bits: n,
1223                 size,
1224             })
1225         },
1226         LitKind::Float(n, fty) => {
1227             parse_float(n, fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
1228         }
1229         LitKind::FloatUnsuffixed(n) => {
1230             let fty = match ty.sty {
1231                 ty::Float(fty) => fty,
1232                 _ => bug!()
1233             };
1234             parse_float(n, fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
1235         }
1236         LitKind::Bool(b) => ConstValue::Scalar(Scalar::from_bool(b)),
1237         LitKind::Char(c) => ConstValue::Scalar(Scalar::from_char(c)),
1238     };
1239     Ok(ty::Const::from_const_value(tcx, lit, ty))
1240 }
1241
1242 pub fn parse_float<'tcx>(
1243     num: Symbol,
1244     fty: ast::FloatTy,
1245     neg: bool,
1246 ) -> Result<ConstValue<'tcx>, ()> {
1247     let num = num.as_str();
1248     use rustc_apfloat::ieee::{Single, Double};
1249     use rustc_apfloat::Float;
1250     let (bits, size) = match fty {
1251         ast::FloatTy::F32 => {
1252             num.parse::<f32>().map_err(|_| ())?;
1253             let mut f = num.parse::<Single>().unwrap_or_else(|e| {
1254                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
1255             });
1256             if neg {
1257                 f = -f;
1258             }
1259             (f.to_bits(), 4)
1260         }
1261         ast::FloatTy::F64 => {
1262             num.parse::<f64>().map_err(|_| ())?;
1263             let mut f = num.parse::<Double>().unwrap_or_else(|e| {
1264                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
1265             });
1266             if neg {
1267                 f = -f;
1268             }
1269             (f.to_bits(), 8)
1270         }
1271     };
1272
1273     Ok(ConstValue::Scalar(Scalar::Bits { bits, size }))
1274 }