src/librustc_mir/hair/pattern/mod.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Code to validate patterns/matches
  12
  13 mod _match;
  14 mod check_match;
  15
  16 pub use self::check_match::check_crate;
  17 pub(crate) use self::check_match::check_match;
  18
  19 use const_eval::{const_field, const_variant_index};
  20
  21 use hair::util::UserAnnotatedTyHelpers;
  22
  23 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability, UserTypeAnnotation};
  24 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  25 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty};
  26 use rustc::ty::subst::{Substs, Kind};
  27 use rustc::hir::{self, PatKind, RangeEnd};
  28 use rustc::hir::def::{Def, CtorKind};
  29 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  30
  31 use rustc_data_structures::indexed_vec::Idx;
  32
  33 use std::cmp::Ordering;
  34 use std::fmt;
  35 use syntax::ast;
  36 use syntax::ptr::P;
  37 use syntax_pos::Span;
  38 use syntax_pos::symbol::Symbol;
  39
  40 #[derive(Clone, Debug)]
  41 pub enum PatternError {
  42     AssociatedConstInPattern(Span),
  43     StaticInPattern(Span),
  44     FloatBug,
  45     NonConstPath(Span),
  46 }
  47
  48 #[derive(Copy, Clone, Debug)]
  49 pub enum BindingMode<'tcx> {
  50     ByValue,
  51     ByRef(Region<'tcx>, BorrowKind),
  52 }
  53
  54 #[derive(Clone, Debug)]
  55 pub struct FieldPattern<'tcx> {
  56     pub field: Field,
  57     pub pattern: Pattern<'tcx>,
  58 }
  59
  60 #[derive(Clone, Debug)]
  61 pub struct Pattern<'tcx> {
  62     pub ty: Ty<'tcx>,
  63     pub span: Span,
  64     pub kind: Box<PatternKind<'tcx>>,
  65 }
  66
  67 #[derive(Copy, Clone, Debug)]
  68 pub struct PatternTypeAnnotation<'tcx>(UserTypeAnnotation<'tcx>);
  69
  70 impl<'tcx> PatternTypeAnnotation<'tcx> {
  71     pub(crate) fn from_c_ty(c_ty: ty::CanonicalTy<'tcx>) -> Self {
  72         Self::from_u_ty(UserTypeAnnotation::Ty(c_ty))
  73     }
  74     pub(crate) fn from_u_ty(u_ty: UserTypeAnnotation<'tcx>) -> Self {
  75         PatternTypeAnnotation(u_ty)
  76     }
  77
  78     pub(crate) fn user_ty(self) -> UserTypeAnnotation<'tcx> { self.0 }
  79 }
  80
  81 #[derive(Clone, Debug)]
  82 pub enum PatternKind<'tcx> {
  83     Wild,
  84
  85     AscribeUserType {
  86         user_ty: PatternTypeAnnotation<'tcx>,
  87         subpattern: Pattern<'tcx>,
  88         user_ty_span: Span,
  89     },
  90
  91     /// x, ref x, x @ P, etc
  92     Binding {
  93         mutability: Mutability,
  94         name: ast::Name,
  95         mode: BindingMode<'tcx>,
  96         var: ast::NodeId,
  97         ty: Ty<'tcx>,
  98         subpattern: Option<Pattern<'tcx>>,
  99     },
 100
 101     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
 102     Variant {
 103         adt_def: &'tcx AdtDef,
 104         substs: &'tcx Substs<'tcx>,
 105         variant_index: usize,
 106         subpatterns: Vec<FieldPattern<'tcx>>,
 107     },
 108
 109     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
 110     Leaf {
 111         subpatterns: Vec<FieldPattern<'tcx>>,
 112     },
 113
 114     /// box P, &P, &mut P, etc
 115     Deref {
 116         subpattern: Pattern<'tcx>,
 117     },
 118
 119     Constant {
 120         value: &'tcx ty::Const<'tcx>,
 121     },
 122
 123     Range {
 124         lo: &'tcx ty::Const<'tcx>,
 125         hi: &'tcx ty::Const<'tcx>,
 126         ty: Ty<'tcx>,
 127         end: RangeEnd,
 128     },
 129
 130     /// matches against a slice, checking the length and extracting elements.
 131     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 132     /// e.g. `&[ref xs..]`.
 133     Slice {
 134         prefix: Vec<Pattern<'tcx>>,
 135         slice: Option<Pattern<'tcx>>,
 136         suffix: Vec<Pattern<'tcx>>,
 137     },
 138
 139     /// fixed match against an array, irrefutable
 140     Array {
 141         prefix: Vec<Pattern<'tcx>>,
 142         slice: Option<Pattern<'tcx>>,
 143         suffix: Vec<Pattern<'tcx>>,
 144     },
 145 }
 146
 147 impl<'tcx> fmt::Display for Pattern<'tcx> {
 148     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 149         match *self.kind {
 150             PatternKind::Wild => write!(f, "_"),
 151             PatternKind::AscribeUserType { ref subpattern, .. } =>
 152                 write!(f, "{}: _", subpattern),
 153             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 154                 let is_mut = match mode {
 155                     BindingMode::ByValue => mutability == Mutability::Mut,
 156                     BindingMode::ByRef(_, bk) => {
 157                         write!(f, "ref ")?;
 158                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 159                     }
 160                 };
 161                 if is_mut {
 162                     write!(f, "mut ")?;
 163                 }
 164                 write!(f, "{}", name)?;
 165                 if let Some(ref subpattern) = *subpattern {
 166                     write!(f, " @ {}", subpattern)?;
 167                 }
 168                 Ok(())
 169             }
 170             PatternKind::Variant { ref subpatterns, .. } |
 171             PatternKind::Leaf { ref subpatterns } => {
 172                 let variant = match *self.kind {
 173                     PatternKind::Variant { adt_def, variant_index, .. } => {
 174                         Some(&adt_def.variants[variant_index])
 175                     }
 176                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 177                         if !adt.is_enum() {
 178                             Some(&adt.variants[0])
 179                         } else {
 180                             None
 181                         }
 182                     } else {
 183                         None
 184                     }
 185                 };
 186
 187                 let mut first = true;
 188                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 189
 190                 if let Some(variant) = variant {
 191                     write!(f, "{}", variant.name)?;
 192
 193                     // Only for Adt we can have `S {...}`,
 194                     // which we handle separately here.
 195                     if variant.ctor_kind == CtorKind::Fictive {
 196                         write!(f, " {{ ")?;
 197
 198                         let mut printed = 0;
 199                         for p in subpatterns {
 200                             if let PatternKind::Wild = *p.pattern.kind {
 201                                 continue;
 202                             }
 203                             let name = variant.fields[p.field.index()].ident;
 204                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 205                             printed += 1;
 206                         }
 207
 208                         if printed < variant.fields.len() {
 209                             write!(f, "{}..", start_or_continue())?;
 210                         }
 211
 212                         return write!(f, " }}");
 213                     }
 214                 }
 215
 216                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 217                 if num_fields != 0 || variant.is_none() {
 218                     write!(f, "(")?;
 219                     for i in 0..num_fields {
 220                         write!(f, "{}", start_or_continue())?;
 221
 222                         // Common case: the field is where we expect it.
 223                         if let Some(p) = subpatterns.get(i) {
 224                             if p.field.index() == i {
 225                                 write!(f, "{}", p.pattern)?;
 226                                 continue;
 227                             }
 228                         }
 229
 230                         // Otherwise, we have to go looking for it.
 231                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 232                             write!(f, "{}", p.pattern)?;
 233                         } else {
 234                             write!(f, "_")?;
 235                         }
 236                     }
 237                     write!(f, ")")?;
 238                 }
 239
 240                 Ok(())
 241             }
 242             PatternKind::Deref { ref subpattern } => {
 243                 match self.ty.sty {
 244                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 245                     ty::Ref(_, _, mutbl) => {
 246                         write!(f, "&")?;
 247                         if mutbl == hir::MutMutable {
 248                             write!(f, "mut ")?;
 249                         }
 250                     }
 251                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 252                 }
 253                 write!(f, "{}", subpattern)
 254             }
 255             PatternKind::Constant { value } => {
 256                 fmt_const_val(f, value)
 257             }
 258             PatternKind::Range { lo, hi, ty: _, end } => {
 259                 fmt_const_val(f, lo)?;
 260                 match end {
 261                     RangeEnd::Included => write!(f, "..=")?,
 262                     RangeEnd::Excluded => write!(f, "..")?,
 263                 }
 264                 fmt_const_val(f, hi)
 265             }
 266             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 267             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 268                 let mut first = true;
 269                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 270                 write!(f, "[")?;
 271                 for p in prefix {
 272                     write!(f, "{}{}", start_or_continue(), p)?;
 273                 }
 274                 if let Some(ref slice) = *slice {
 275                     write!(f, "{}", start_or_continue())?;
 276                     match *slice.kind {
 277                         PatternKind::Wild => {}
 278                         _ => write!(f, "{}", slice)?
 279                     }
 280                     write!(f, "..")?;
 281                 }
 282                 for p in suffix {
 283                     write!(f, "{}{}", start_or_continue(), p)?;
 284                 }
 285                 write!(f, "]")
 286             }
 287         }
 288     }
 289 }
 290
 291 pub struct PatternContext<'a, 'tcx: 'a> {
 292     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 293     pub param_env: ty::ParamEnv<'tcx>,
 294     pub tables: &'a ty::TypeckTables<'tcx>,
 295     pub substs: &'tcx Substs<'tcx>,
 296     pub errors: Vec<PatternError>,
 297 }
 298
 299 impl<'a, 'tcx> Pattern<'tcx> {
 300     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 301                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 302                     tables: &'a ty::TypeckTables<'tcx>,
 303                     pat: &'tcx hir::Pat) -> Self {
 304         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 305         let result = pcx.lower_pattern(pat);
 306         if !pcx.errors.is_empty() {
 307             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 308             tcx.sess.delay_span_bug(pat.span, &msg);
 309         }
 310         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 311         result
 312     }
 313 }
 314
 315 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 316     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 317                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 318                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 319         PatternContext {
 320             tcx,
 321             param_env: param_env_and_substs.param_env,
 322             tables,
 323             substs: param_env_and_substs.value,
 324             errors: vec![]
 325         }
 326     }
 327
 328     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 329         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 330         // pattern has the type that results *after* dereferencing. For example, in this code:
 331         //
 332         // ```
 333         // match &&Some(0i32) {
 334         //     Some(n) => { ... },
 335         //     _ => { ... },
 336         // }
 337         // ```
 338         //
 339         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 340         // determined in rustc_typeck::check::match). The adjustments would be
 341         //
 342         // `vec![&&Option<i32>, &Option<i32>]`.
 343         //
 344         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 345         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 346         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 347         // gets the least-dereferenced type).
 348         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 349         self.tables
 350             .pat_adjustments()
 351             .get(pat.hir_id)
 352             .unwrap_or(&vec![])
 353             .iter()
 354             .rev()
 355             .fold(unadjusted_pat, |pat, ref_ty| {
 356                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 357                     Pattern {
 358                         span: pat.span,
 359                         ty: ref_ty,
 360                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 361                     }
 362                 },
 363             )
 364     }
 365
 366     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 367         let mut ty = self.tables.node_id_to_type(pat.hir_id);
 368
 369         let kind = match pat.node {
 370             PatKind::Wild => PatternKind::Wild,
 371
 372             PatKind::Lit(ref value) => self.lower_lit(value),
 373
 374             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 375                 match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
 376                     (PatternKind::Constant { value: lo },
 377                      PatternKind::Constant { value: hi }) => {
 378                         use std::cmp::Ordering;
 379                         let cmp = compare_const_vals(
 380                             self.tcx,
 381                             lo,
 382                             hi,
 383                             self.param_env.and(ty),
 384                         );
 385                         match (end, cmp) {
 386                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 387                                 PatternKind::Range { lo, hi, ty, end },
 388                             (RangeEnd::Excluded, _) => {
 389                                 span_err!(
 390                                     self.tcx.sess,
 391                                     lo_expr.span,
 392                                     E0579,
 393                                     "lower range bound must be less than upper",
 394                                 );
 395                                 PatternKind::Wild
 396                             }
 397                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 398                                 PatternKind::Constant { value: lo }
 399                             }
 400                             (RangeEnd::Included, Some(Ordering::Less)) => {
 401                                 PatternKind::Range { lo, hi, ty, end }
 402                             }
 403                             (RangeEnd::Included, _) => {
 404                                 let mut err = struct_span_err!(
 405                                     self.tcx.sess,
 406                                     lo_expr.span,
 407                                     E0030,
 408                                     "lower range bound must be less than or equal to upper"
 409                                 );
 410                                 err.span_label(
 411                                     lo_expr.span,
 412                                     "lower bound larger than upper bound",
 413                                 );
 414                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 415                                     err.note("When matching against a range, the compiler \
 416                                               verifies that the range is non-empty. Range \
 417                                               patterns include both end-points, so this is \
 418                                               equivalent to requiring the start of the range \
 419                                               to be less than or equal to the end of the range.");
 420                                 }
 421                                 err.emit();
 422                                 PatternKind::Wild
 423                             }
 424                         }
 425                     }
 426                     _ => PatternKind::Wild
 427                 }
 428             }
 429
 430             PatKind::Path(ref qpath) => {
 431                 return self.lower_path(qpath, pat.hir_id, pat.span);
 432             }
 433
 434             PatKind::Ref(ref subpattern, _) |
 435             PatKind::Box(ref subpattern) => {
 436                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 437             }
 438
 439             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 440                 match ty.sty {
 441                     ty::Ref(_, ty, _) =>
 442                         PatternKind::Deref {
 443                             subpattern: Pattern {
 444                                 ty,
 445                                 span: pat.span,
 446                                 kind: Box::new(self.slice_or_array_pattern(
 447                                     pat.span, ty, prefix, slice, suffix))
 448                             },
 449                         },
 450                     ty::Slice(..) |
 451                     ty::Array(..) =>
 452                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 453                     ty::Error => { // Avoid ICE
 454                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 455                     }
 456                     ref sty =>
 457                         span_bug!(
 458                             pat.span,
 459                             "unexpanded type for vector pattern: {:?}",
 460                             sty),
 461                 }
 462             }
 463
 464             PatKind::Tuple(ref subpatterns, ddpos) => {
 465                 match ty.sty {
 466                     ty::Tuple(ref tys) => {
 467                         let subpatterns =
 468                             subpatterns.iter()
 469                                        .enumerate_and_adjust(tys.len(), ddpos)
 470                                        .map(|(i, subpattern)| FieldPattern {
 471                                             field: Field::new(i),
 472                                             pattern: self.lower_pattern(subpattern)
 473                                        })
 474                                        .collect();
 475
 476                         PatternKind::Leaf { subpatterns: subpatterns }
 477                     }
 478                     ty::Error => { // Avoid ICE (#50577)
 479                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 480                     }
 481                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 482                 }
 483             }
 484
 485             PatKind::Binding(_, id, ident, ref sub) => {
 486                 let var_ty = self.tables.node_id_to_type(pat.hir_id);
 487                 let region = match var_ty.sty {
 488                     ty::Ref(r, _, _) => Some(r),
 489                     ty::Error => { // Avoid ICE
 490                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 491                     }
 492                     _ => None,
 493                 };
 494                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 495                                                          .expect("missing binding mode");
 496                 let (mutability, mode) = match bm {
 497                     ty::BindByValue(hir::MutMutable) =>
 498                         (Mutability::Mut, BindingMode::ByValue),
 499                     ty::BindByValue(hir::MutImmutable) =>
 500                         (Mutability::Not, BindingMode::ByValue),
 501                     ty::BindByReference(hir::MutMutable) =>
 502                         (Mutability::Not, BindingMode::ByRef(
 503                             region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
 504                     ty::BindByReference(hir::MutImmutable) =>
 505                         (Mutability::Not, BindingMode::ByRef(
 506                             region.unwrap(), BorrowKind::Shared)),
 507                 };
 508
 509                 // A ref x pattern is the same node used for x, and as such it has
 510                 // x's type, which is &T, where we want T (the type being matched).
 511                 if let ty::BindByReference(_) = bm {
 512                     if let ty::Ref(_, rty, _) = ty.sty {
 513                         ty = rty;
 514                     } else {
 515                         bug!("`ref {}` has wrong type {}", ident, ty);
 516                     }
 517                 }
 518
 519                 PatternKind::Binding {
 520                     mutability,
 521                     mode,
 522                     name: ident.name,
 523                     var: id,
 524                     ty: var_ty,
 525                     subpattern: self.lower_opt_pattern(sub),
 526                 }
 527             }
 528
 529             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 530                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 531                 let adt_def = match ty.sty {
 532                     ty::Adt(adt_def, _) => adt_def,
 533                     ty::Error => { // Avoid ICE (#50585)
 534                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 535                     }
 536                     _ => span_bug!(pat.span,
 537                                    "tuple struct pattern not applied to an ADT {:?}",
 538                                    ty.sty),
 539                 };
 540                 let variant_def = adt_def.variant_of_def(def);
 541
 542                 let subpatterns =
 543                         subpatterns.iter()
 544                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 545                                    .map(|(i, field)| FieldPattern {
 546                                        field: Field::new(i),
 547                                        pattern: self.lower_pattern(field),
 548                                    })
 549                     .collect();
 550
 551                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 552             }
 553
 554             PatKind::Struct(ref qpath, ref fields, _) => {
 555                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 556                 let subpatterns =
 557                     fields.iter()
 558                           .map(|field| {
 559                               FieldPattern {
 560                                   field: Field::new(self.tcx.field_index(field.node.id,
 561                                                                          self.tables)),
 562                                   pattern: self.lower_pattern(&field.node.pat),
 563                               }
 564                           })
 565                           .collect();
 566
 567                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 568             }
 569         };
 570
 571         Pattern {
 572             span: pat.span,
 573             ty,
 574             kind: Box::new(kind),
 575         }
 576     }
 577
 578     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 579         pats.iter().map(|p| self.lower_pattern(p)).collect()
 580     }
 581
 582     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 583     {
 584         pat.as_ref().map(|p| self.lower_pattern(p))
 585     }
 586
 587     fn flatten_nested_slice_patterns(
 588         &mut self,
 589         prefix: Vec<Pattern<'tcx>>,
 590         slice: Option<Pattern<'tcx>>,
 591         suffix: Vec<Pattern<'tcx>>)
 592         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 593     {
 594         let orig_slice = match slice {
 595             Some(orig_slice) => orig_slice,
 596             None => return (prefix, slice, suffix)
 597         };
 598         let orig_prefix = prefix;
 599         let orig_suffix = suffix;
 600
 601         // dance because of intentional borrow-checker stupidity.
 602         let kind = *orig_slice.kind;
 603         match kind {
 604             PatternKind::Slice { prefix, slice, mut suffix } |
 605             PatternKind::Array { prefix, slice, mut suffix } => {
 606                 let mut orig_prefix = orig_prefix;
 607
 608                 orig_prefix.extend(prefix);
 609                 suffix.extend(orig_suffix);
 610
 611                 (orig_prefix, slice, suffix)
 612             }
 613             _ => {
 614                 (orig_prefix, Some(Pattern {
 615                     kind: box kind, ..orig_slice
 616                 }), orig_suffix)
 617             }
 618         }
 619     }
 620
 621     fn slice_or_array_pattern(
 622         &mut self,
 623         span: Span,
 624         ty: Ty<'tcx>,
 625         prefix: &'tcx [P<hir::Pat>],
 626         slice: &'tcx Option<P<hir::Pat>>,
 627         suffix: &'tcx [P<hir::Pat>])
 628         -> PatternKind<'tcx>
 629     {
 630         let prefix = self.lower_patterns(prefix);
 631         let slice = self.lower_opt_pattern(slice);
 632         let suffix = self.lower_patterns(suffix);
 633         let (prefix, slice, suffix) =
 634             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 635
 636         match ty.sty {
 637             ty::Slice(..) => {
 638                 // matching a slice or fixed-length array
 639                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 640             }
 641
 642             ty::Array(_, len) => {
 643                 // fixed-length array
 644                 let len = len.unwrap_usize(self.tcx);
 645                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 646                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 647             }
 648
 649             _ => {
 650                 span_bug!(span, "bad slice pattern type {:?}", ty);
 651             }
 652         }
 653     }
 654
 655     fn lower_variant_or_leaf(
 656         &mut self,
 657         def: Def,
 658         hir_id: hir::HirId,
 659         span: Span,
 660         ty: Ty<'tcx>,
 661         subpatterns: Vec<FieldPattern<'tcx>>,
 662     ) -> PatternKind<'tcx> {
 663         let mut kind = match def {
 664             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 665                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 666                 let adt_def = self.tcx.adt_def(enum_id);
 667                 if adt_def.is_enum() {
 668                     let substs = match ty.sty {
 669                         ty::Adt(_, substs) |
 670                         ty::FnDef(_, substs) => substs,
 671                         ty::Error => {  // Avoid ICE (#50585)
 672                             return PatternKind::Wild;
 673                         }
 674                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 675                     };
 676                     PatternKind::Variant {
 677                         adt_def,
 678                         substs,
 679                         variant_index: adt_def.variant_index_with_id(variant_id),
 680                         subpatterns,
 681                     }
 682                 } else {
 683                     PatternKind::Leaf { subpatterns: subpatterns }
 684                 }
 685             }
 686
 687             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 688             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) => {
 689                 PatternKind::Leaf { subpatterns: subpatterns }
 690             }
 691
 692             _ => {
 693                 self.errors.push(PatternError::NonConstPath(span));
 694                 PatternKind::Wild
 695             }
 696         };
 697
 698         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 699             let subpattern = Pattern {
 700                 span,
 701                 ty,
 702                 kind: Box::new(kind),
 703             };
 704
 705             debug!("pattern user_ty = {:?} for pattern at {:?}", user_ty, span);
 706
 707             let pat_ty = PatternTypeAnnotation::from_u_ty(user_ty);
 708             kind = PatternKind::AscribeUserType {
 709                 subpattern,
 710                 user_ty: pat_ty,
 711                 user_ty_span: span,
 712             };
 713         }
 714
 715         kind
 716     }
 717
 718     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 719     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 720     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 721     fn lower_path(&mut self,
 722                   qpath: &hir::QPath,
 723                   id: hir::HirId,
 724                   span: Span)
 725                   -> Pattern<'tcx> {
 726         let ty = self.tables.node_id_to_type(id);
 727         let def = self.tables.qpath_def(qpath, id);
 728         let is_associated_const = match def {
 729             Def::AssociatedConst(_) => true,
 730             _ => false,
 731         };
 732         let kind = match def {
 733             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 734                 let substs = self.tables.node_substs(id);
 735                 match ty::Instance::resolve(
 736                     self.tcx,
 737                     self.param_env,
 738                     def_id,
 739                     substs,
 740                 ) {
 741                     Some(instance) => {
 742                         let cid = GlobalId {
 743                             instance,
 744                             promoted: None,
 745                         };
 746                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 747                             Ok(value) => {
 748                                 return self.const_to_pat(instance, value, id, span)
 749                             },
 750                             Err(_) => {
 751                                 self.tcx.sess.span_err(
 752                                     span,
 753                                     "could not evaluate constant pattern",
 754                                 );
 755                                 PatternKind::Wild
 756                             }
 757                         }
 758                     },
 759                     None => {
 760                         self.errors.push(if is_associated_const {
 761                             PatternError::AssociatedConstInPattern(span)
 762                         } else {
 763                             PatternError::StaticInPattern(span)
 764                         });
 765                         PatternKind::Wild
 766                     },
 767                 }
 768             }
 769             _ => self.lower_variant_or_leaf(def, id, span, ty, vec![]),
 770         };
 771
 772         Pattern {
 773             span,
 774             ty,
 775             kind: Box::new(kind),
 776         }
 777     }
 778
 779     /// Converts literals, paths and negation of literals to patterns.
 780     /// The special case for negation exists to allow things like -128i8
 781     /// which would overflow if we tried to evaluate 128i8 and then negate
 782     /// afterwards.
 783     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 784         match expr.node {
 785             hir::ExprKind::Lit(ref lit) => {
 786                 let ty = self.tables.expr_ty(expr);
 787                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 788                     Ok(val) => {
 789                         let instance = ty::Instance::new(
 790                             self.tables.local_id_root.expect("literal outside any scope"),
 791                             self.substs,
 792                         );
 793                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 794                     },
 795                     Err(e) => {
 796                         if e == LitToConstError::UnparseableFloat {
 797                             self.errors.push(PatternError::FloatBug);
 798                         }
 799                         PatternKind::Wild
 800                     },
 801                 }
 802             },
 803             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 804             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 805                 let ty = self.tables.expr_ty(expr);
 806                 let lit = match expr.node {
 807                     hir::ExprKind::Lit(ref lit) => lit,
 808                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 809                 };
 810                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 811                     Ok(val) => {
 812                         let instance = ty::Instance::new(
 813                             self.tables.local_id_root.expect("literal outside any scope"),
 814                             self.substs,
 815                         );
 816                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 817                     },
 818                     Err(e) => {
 819                         if e == LitToConstError::UnparseableFloat {
 820                             self.errors.push(PatternError::FloatBug);
 821                         }
 822                         PatternKind::Wild
 823                     },
 824                 }
 825             }
 826             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 827         }
 828     }
 829
 830     /// Converts an evaluated constant to a pattern (if possible).
 831     /// This means aggregate values (like structs and enums) are converted
 832     /// to a pattern that matches the value (as if you'd compare via eq).
 833     fn const_to_pat(
 834         &self,
 835         instance: ty::Instance<'tcx>,
 836         cv: &'tcx ty::Const<'tcx>,
 837         id: hir::HirId,
 838         span: Span,
 839     ) -> Pattern<'tcx> {
 840         debug!("const_to_pat: cv={:#?}", cv);
 841         let adt_subpattern = |i, variant_opt| {
 842             let field = Field::new(i);
 843             let val = const_field(
 844                 self.tcx, self.param_env, instance,
 845                 variant_opt, field, cv,
 846             ).expect("field access failed");
 847             self.const_to_pat(instance, val, id, span)
 848         };
 849         let adt_subpatterns = |n, variant_opt| {
 850             (0..n).map(|i| {
 851                 let field = Field::new(i);
 852                 FieldPattern {
 853                     field,
 854                     pattern: adt_subpattern(i, variant_opt),
 855                 }
 856             }).collect::<Vec<_>>()
 857         };
 858         let kind = match cv.ty.sty {
 859             ty::Float(_) => {
 860                 let id = self.tcx.hir.hir_to_node_id(id);
 861                 self.tcx.lint_node(
 862                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 863                     id,
 864                     span,
 865                     "floating-point types cannot be used in patterns",
 866                 );
 867                 PatternKind::Constant {
 868                     value: cv,
 869                 }
 870             },
 871             ty::Adt(adt_def, _) if adt_def.is_union() => {
 872                 // Matching on union fields is unsafe, we can't hide it in constants
 873                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 874                 PatternKind::Wild
 875             }
 876             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 877                 let msg = format!("to use a constant of type `{}` in a pattern, \
 878                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 879                                     self.tcx.item_path_str(adt_def.did),
 880                                     self.tcx.item_path_str(adt_def.did));
 881                 self.tcx.sess.span_err(span, &msg);
 882                 PatternKind::Wild
 883             },
 884             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 885                 let variant_index = const_variant_index(
 886                     self.tcx, self.param_env, instance, cv
 887                 ).expect("const_variant_index failed");
 888                 let subpatterns = adt_subpatterns(
 889                     adt_def.variants[variant_index].fields.len(),
 890                     Some(variant_index),
 891                 );
 892                 PatternKind::Variant {
 893                     adt_def,
 894                     substs,
 895                     variant_index,
 896                     subpatterns,
 897                 }
 898             },
 899             ty::Adt(adt_def, _) => {
 900                 let struct_var = adt_def.non_enum_variant();
 901                 PatternKind::Leaf {
 902                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
 903                 }
 904             }
 905             ty::Tuple(fields) => {
 906                 PatternKind::Leaf {
 907                     subpatterns: adt_subpatterns(fields.len(), None),
 908                 }
 909             }
 910             ty::Array(_, n) => {
 911                 PatternKind::Array {
 912                     prefix: (0..n.unwrap_usize(self.tcx))
 913                         .map(|i| adt_subpattern(i as usize, None))
 914                         .collect(),
 915                     slice: None,
 916                     suffix: Vec::new(),
 917                 }
 918             }
 919             _ => {
 920                 PatternKind::Constant {
 921                     value: cv,
 922                 }
 923             },
 924         };
 925
 926         Pattern {
 927             span,
 928             ty: cv.ty,
 929             kind: Box::new(kind),
 930         }
 931     }
 932 }
 933
 934 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
 935     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
 936         self.tcx
 937     }
 938
 939     fn tables(&self) -> &ty::TypeckTables<'tcx> {
 940         self.tables
 941     }
 942 }
 943
 944
 945 pub trait PatternFoldable<'tcx> : Sized {
 946     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 947         self.super_fold_with(folder)
 948     }
 949
 950     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
 951 }
 952
 953 pub trait PatternFolder<'tcx> : Sized {
 954     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
 955         pattern.super_fold_with(self)
 956     }
 957
 958     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
 959         kind.super_fold_with(self)
 960     }
 961 }
 962
 963
 964 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
 965     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 966         let content: T = (**self).fold_with(folder);
 967         box content
 968     }
 969 }
 970
 971 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
 972     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 973         self.iter().map(|t| t.fold_with(folder)).collect()
 974     }
 975 }
 976
 977 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
 978     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
 979         self.as_ref().map(|t| t.fold_with(folder))
 980     }
 981 }
 982
 983 macro_rules! CloneImpls {
 984     (<$lt_tcx:tt> $($ty:ty),+) => {
 985         $(
 986             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
 987                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
 988                     Clone::clone(self)
 989                 }
 990             }
 991         )+
 992     }
 993 }
 994
 995 CloneImpls!{ <'tcx>
 996     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
 997     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
 998     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, UserTypeAnnotation<'tcx>, PatternTypeAnnotation<'tcx>
 999 }
1000
1001 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1002     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1003         FieldPattern {
1004             field: self.field.fold_with(folder),
1005             pattern: self.pattern.fold_with(folder)
1006         }
1007     }
1008 }
1009
1010 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1011     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1012         folder.fold_pattern(self)
1013     }
1014
1015     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1016         Pattern {
1017             ty: self.ty.fold_with(folder),
1018             span: self.span.fold_with(folder),
1019             kind: self.kind.fold_with(folder)
1020         }
1021     }
1022 }
1023
1024 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1025     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1026         folder.fold_pattern_kind(self)
1027     }
1028
1029     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1030         match *self {
1031             PatternKind::Wild => PatternKind::Wild,
1032             PatternKind::AscribeUserType {
1033                 ref subpattern,
1034                 user_ty,
1035                 user_ty_span,
1036             } => PatternKind::AscribeUserType {
1037                 subpattern: subpattern.fold_with(folder),
1038                 user_ty: user_ty.fold_with(folder),
1039                 user_ty_span,
1040             },
1041             PatternKind::Binding {
1042                 mutability,
1043                 name,
1044                 mode,
1045                 var,
1046                 ty,
1047                 ref subpattern,
1048             } => PatternKind::Binding {
1049                 mutability: mutability.fold_with(folder),
1050                 name: name.fold_with(folder),
1051                 mode: mode.fold_with(folder),
1052                 var: var.fold_with(folder),
1053                 ty: ty.fold_with(folder),
1054                 subpattern: subpattern.fold_with(folder),
1055             },
1056             PatternKind::Variant {
1057                 adt_def,
1058                 substs,
1059                 variant_index,
1060                 ref subpatterns,
1061             } => PatternKind::Variant {
1062                 adt_def: adt_def.fold_with(folder),
1063                 substs: substs.fold_with(folder),
1064                 variant_index: variant_index.fold_with(folder),
1065                 subpatterns: subpatterns.fold_with(folder)
1066             },
1067             PatternKind::Leaf {
1068                 ref subpatterns,
1069             } => PatternKind::Leaf {
1070                 subpatterns: subpatterns.fold_with(folder),
1071             },
1072             PatternKind::Deref {
1073                 ref subpattern,
1074             } => PatternKind::Deref {
1075                 subpattern: subpattern.fold_with(folder),
1076             },
1077             PatternKind::Constant {
1078                 value
1079             } => PatternKind::Constant {
1080                 value: value.fold_with(folder)
1081             },
1082             PatternKind::Range {
1083                 lo,
1084                 hi,
1085                 ty,
1086                 end,
1087             } => PatternKind::Range {
1088                 lo: lo.fold_with(folder),
1089                 hi: hi.fold_with(folder),
1090                 ty: ty.fold_with(folder),
1091                 end,
1092             },
1093             PatternKind::Slice {
1094                 ref prefix,
1095                 ref slice,
1096                 ref suffix,
1097             } => PatternKind::Slice {
1098                 prefix: prefix.fold_with(folder),
1099                 slice: slice.fold_with(folder),
1100                 suffix: suffix.fold_with(folder)
1101             },
1102             PatternKind::Array {
1103                 ref prefix,
1104                 ref slice,
1105                 ref suffix
1106             } => PatternKind::Array {
1107                 prefix: prefix.fold_with(folder),
1108                 slice: slice.fold_with(folder),
1109                 suffix: suffix.fold_with(folder)
1110             },
1111         }
1112     }
1113 }
1114
1115 pub fn compare_const_vals<'a, 'tcx>(
1116     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1117     a: &'tcx ty::Const<'tcx>,
1118     b: &'tcx ty::Const<'tcx>,
1119     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1120 ) -> Option<Ordering> {
1121     trace!("compare_const_vals: {:?}, {:?}", a, b);
1122
1123     let from_bool = |v: bool| {
1124         if v {
1125             Some(Ordering::Equal)
1126         } else {
1127             None
1128         }
1129     };
1130
1131     let fallback = || from_bool(a == b);
1132
1133     // Use the fallback if any type differs
1134     if a.ty != b.ty || a.ty != ty.value {
1135         return fallback();
1136     }
1137
1138     // FIXME: This should use assert_bits(ty) instead of use_bits
1139     // but triggers possibly bugs due to mismatching of arrays and slices
1140     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1141         use ::rustc_apfloat::Float;
1142         return match ty.value.sty {
1143             ty::Float(ast::FloatTy::F32) => {
1144                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1145                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1146                 l.partial_cmp(&r)
1147             },
1148             ty::Float(ast::FloatTy::F64) => {
1149                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1150                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1151                 l.partial_cmp(&r)
1152             },
1153             ty::Int(_) => {
1154                 let layout = tcx.layout_of(ty).ok()?;
1155                 assert!(layout.abi.is_signed());
1156                 let a = sign_extend(a, layout.size);
1157                 let b = sign_extend(b, layout.size);
1158                 Some((a as i128).cmp(&(b as i128)))
1159             },
1160             _ => Some(a.cmp(&b)),
1161         }
1162     }
1163
1164     if let ty::Ref(_, rty, _) = ty.value.sty {
1165         if let ty::Str = rty.sty {
1166             match (a.val, b.val) {
1167                 (
1168                     ConstValue::ScalarPair(
1169                         Scalar::Ptr(ptr_a),
1170                         len_a,
1171                     ),
1172                     ConstValue::ScalarPair(
1173                         Scalar::Ptr(ptr_b),
1174                         len_b,
1175                     ),
1176                 ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1177                     if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1178                         if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1179                             if len_a == len_b {
1180                                 let map = tcx.alloc_map.lock();
1181                                 let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1182                                 let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1183                                 if alloc_a.bytes.len() as u128 == len_a {
1184                                     return from_bool(alloc_a == alloc_b);
1185                                 }
1186                             }
1187                         }
1188                     }
1189                 }
1190                 _ => (),
1191             }
1192         }
1193     }
1194
1195     fallback()
1196 }
1197
1198 #[derive(PartialEq)]
1199 enum LitToConstError {
1200     UnparseableFloat,
1201     Propagated,
1202 }
1203
1204 // FIXME: Combine with rustc_mir::hair::cx::const_eval_literal
1205 fn lit_to_const<'a, 'tcx>(lit: &'tcx ast::LitKind,
1206                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
1207                           ty: Ty<'tcx>,
1208                           neg: bool)
1209                           -> Result<&'tcx ty::Const<'tcx>, LitToConstError> {
1210     use syntax::ast::*;
1211
1212     use rustc::mir::interpret::*;
1213     let lit = match *lit {
1214         LitKind::Str(ref s, _) => {
1215             let s = s.as_str();
1216             let id = tcx.allocate_bytes(s.as_bytes());
1217             ConstValue::new_slice(Scalar::Ptr(id.into()), s.len() as u64, tcx)
1218         },
1219         LitKind::ByteStr(ref data) => {
1220             let id = tcx.allocate_bytes(data);
1221             ConstValue::Scalar(Scalar::Ptr(id.into()))
1222         },
1223         LitKind::Byte(n) => ConstValue::Scalar(Scalar::Bits {
1224             bits: n as u128,
1225             size: 1,
1226         }),
1227         LitKind::Int(n, _) => {
1228             enum Int {
1229                 Signed(IntTy),
1230                 Unsigned(UintTy),
1231             }
1232             let ity = match ty.sty {
1233                 ty::Int(IntTy::Isize) => Int::Signed(tcx.sess.target.isize_ty),
1234                 ty::Int(other) => Int::Signed(other),
1235                 ty::Uint(UintTy::Usize) => Int::Unsigned(tcx.sess.target.usize_ty),
1236                 ty::Uint(other) => Int::Unsigned(other),
1237                 ty::Error => { // Avoid ICE (#51963)
1238                     return Err(LitToConstError::Propagated);
1239                 }
1240                 _ => bug!("literal integer type with bad type ({:?})", ty.sty),
1241             };
1242             // This converts from LitKind::Int (which is sign extended) to
1243             // Scalar::Bytes (which is zero extended)
1244             let n = match ity {
1245                 // FIXME(oli-obk): are these casts correct?
1246                 Int::Signed(IntTy::I8) if neg =>
1247                     (n as i8).overflowing_neg().0 as u8 as u128,
1248                 Int::Signed(IntTy::I16) if neg =>
1249                     (n as i16).overflowing_neg().0 as u16 as u128,
1250                 Int::Signed(IntTy::I32) if neg =>
1251                     (n as i32).overflowing_neg().0 as u32 as u128,
1252                 Int::Signed(IntTy::I64) if neg =>
1253                     (n as i64).overflowing_neg().0 as u64 as u128,
1254                 Int::Signed(IntTy::I128) if neg =>
1255                     (n as i128).overflowing_neg().0 as u128,
1256                 Int::Signed(IntTy::I8) | Int::Unsigned(UintTy::U8) => n as u8 as u128,
1257                 Int::Signed(IntTy::I16) | Int::Unsigned(UintTy::U16) => n as u16 as u128,
1258                 Int::Signed(IntTy::I32) | Int::Unsigned(UintTy::U32) => n as u32 as u128,
1259                 Int::Signed(IntTy::I64) | Int::Unsigned(UintTy::U64) => n as u64 as u128,
1260                 Int::Signed(IntTy::I128)| Int::Unsigned(UintTy::U128) => n,
1261                 _ => bug!(),
1262             };
1263             let size = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap().size.bytes() as u8;
1264             ConstValue::Scalar(Scalar::Bits {
1265                 bits: n,
1266                 size,
1267             })
1268         },
1269         LitKind::Float(n, fty) => {
1270             parse_float(n, fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
1271         }
1272         LitKind::FloatUnsuffixed(n) => {
1273             let fty = match ty.sty {
1274                 ty::Float(fty) => fty,
1275                 _ => bug!()
1276             };
1277             parse_float(n, fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
1278         }
1279         LitKind::Bool(b) => ConstValue::Scalar(Scalar::from_bool(b)),
1280         LitKind::Char(c) => ConstValue::Scalar(Scalar::from_char(c)),
1281     };
1282     Ok(ty::Const::from_const_value(tcx, lit, ty))
1283 }
1284
1285 pub fn parse_float<'tcx>(
1286     num: Symbol,
1287     fty: ast::FloatTy,
1288     neg: bool,
1289 ) -> Result<ConstValue<'tcx>, ()> {
1290     let num = num.as_str();
1291     use rustc_apfloat::ieee::{Single, Double};
1292     use rustc_apfloat::Float;
1293     let (bits, size) = match fty {
1294         ast::FloatTy::F32 => {
1295             num.parse::<f32>().map_err(|_| ())?;
1296             let mut f = num.parse::<Single>().unwrap_or_else(|e| {
1297                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
1298             });
1299             if neg {
1300                 f = -f;
1301             }
1302             (f.to_bits(), 4)
1303         }
1304         ast::FloatTy::F64 => {
1305             num.parse::<f64>().map_err(|_| ())?;
1306             let mut f = num.parse::<Double>().unwrap_or_else(|e| {
1307                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
1308             });
1309             if neg {
1310                 f = -f;
1311             }
1312             (f.to_bits(), 8)
1313         }
1314     };
1315
1316     Ok(ConstValue::Scalar(Scalar::Bits { bits, size }))
1317 }