src/librustc_const_eval/pattern.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 use eval;
  12
  13 use rustc::lint;
  14 use rustc::middle::const_val::{ConstEvalErr, ConstVal};
  15 use rustc::mir::{Field, BorrowKind, Mutability};
  16 use rustc::ty::{self, TyCtxt, AdtDef, Ty, TypeVariants, Region};
  17 use rustc::ty::subst::{Substs, Kind};
  18 use rustc::hir::{self, PatKind, RangeEnd};
  19 use rustc::hir::def::{Def, CtorKind};
  20 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  21
  22 use rustc_data_structures::indexed_vec::Idx;
  23
  24 use std::fmt;
  25 use syntax::ast;
  26 use syntax::ptr::P;
  27 use syntax_pos::Span;
  28
  29 #[derive(Clone, Debug)]
  30 pub enum PatternError<'tcx> {
  31     StaticInPattern(Span),
  32     ConstEval(ConstEvalErr<'tcx>),
  33 }
  34
  35 #[derive(Copy, Clone, Debug)]
  36 pub enum BindingMode<'tcx> {
  37     ByValue,
  38     ByRef(&'tcx Region, BorrowKind),
  39 }
  40
  41 #[derive(Clone, Debug)]
  42 pub struct FieldPattern<'tcx> {
  43     pub field: Field,
  44     pub pattern: Pattern<'tcx>,
  45 }
  46
  47 #[derive(Clone, Debug)]
  48 pub struct Pattern<'tcx> {
  49     pub ty: Ty<'tcx>,
  50     pub span: Span,
  51     pub kind: Box<PatternKind<'tcx>>,
  52 }
  53
  54 #[derive(Clone, Debug)]
  55 pub enum PatternKind<'tcx> {
  56     Wild,
  57
  58     /// x, ref x, x @ P, etc
  59     Binding {
  60         mutability: Mutability,
  61         name: ast::Name,
  62         mode: BindingMode<'tcx>,
  63         var: ast::NodeId,
  64         ty: Ty<'tcx>,
  65         subpattern: Option<Pattern<'tcx>>,
  66     },
  67
  68     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
  69     Variant {
  70         adt_def: &'tcx AdtDef,
  71         substs: &'tcx Substs<'tcx>,
  72         variant_index: usize,
  73         subpatterns: Vec<FieldPattern<'tcx>>,
  74     },
  75
  76     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
  77     Leaf {
  78         subpatterns: Vec<FieldPattern<'tcx>>,
  79     },
  80
  81     /// box P, &P, &mut P, etc
  82     Deref {
  83         subpattern: Pattern<'tcx>,
  84     },
  85
  86     Constant {
  87         value: ConstVal<'tcx>,
  88     },
  89
  90     Range {
  91         lo: ConstVal<'tcx>,
  92         hi: ConstVal<'tcx>,
  93         end: RangeEnd,
  94     },
  95
  96     /// matches against a slice, checking the length and extracting elements
  97     Slice {
  98         prefix: Vec<Pattern<'tcx>>,
  99         slice: Option<Pattern<'tcx>>,
 100         suffix: Vec<Pattern<'tcx>>,
 101     },
 102
 103     /// fixed match against an array, irrefutable
 104     Array {
 105         prefix: Vec<Pattern<'tcx>>,
 106         slice: Option<Pattern<'tcx>>,
 107         suffix: Vec<Pattern<'tcx>>,
 108     },
 109 }
 110
 111 fn print_const_val(value: &ConstVal, f: &mut fmt::Formatter) -> fmt::Result {
 112     match *value {
 113         ConstVal::Float(ref x) => write!(f, "{}", x),
 114         ConstVal::Integral(ref i) => write!(f, "{}", i),
 115         ConstVal::Str(ref s) => write!(f, "{:?}", &s[..]),
 116         ConstVal::ByteStr(ref b) => write!(f, "{:?}", &b[..]),
 117         ConstVal::Bool(b) => write!(f, "{:?}", b),
 118         ConstVal::Char(c) => write!(f, "{:?}", c),
 119         ConstVal::Struct(_) |
 120         ConstVal::Tuple(_) |
 121         ConstVal::Function(..) |
 122         ConstVal::Array(..) |
 123         ConstVal::Repeat(..) => bug!("{:?} not printable in a pattern", value)
 124     }
 125 }
 126
 127 impl<'tcx> fmt::Display for Pattern<'tcx> {
 128     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 129         match *self.kind {
 130             PatternKind::Wild => write!(f, "_"),
 131             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 132                 let is_mut = match mode {
 133                     BindingMode::ByValue => mutability == Mutability::Mut,
 134                     BindingMode::ByRef(_, bk) => {
 135                         write!(f, "ref ")?;
 136                         bk == BorrowKind::Mut
 137                     }
 138                 };
 139                 if is_mut {
 140                     write!(f, "mut ")?;
 141                 }
 142                 write!(f, "{}", name)?;
 143                 if let Some(ref subpattern) = *subpattern {
 144                     write!(f, " @ {}", subpattern)?;
 145                 }
 146                 Ok(())
 147             }
 148             PatternKind::Variant { ref subpatterns, .. } |
 149             PatternKind::Leaf { ref subpatterns } => {
 150                 let variant = match *self.kind {
 151                     PatternKind::Variant { adt_def, variant_index, .. } => {
 152                         Some(&adt_def.variants[variant_index])
 153                     }
 154                     _ => if let ty::TyAdt(adt, _) = self.ty.sty {
 155                         if adt.is_univariant() {
 156                             Some(&adt.variants[0])
 157                         } else {
 158                             None
 159                         }
 160                     } else {
 161                         None
 162                     }
 163                 };
 164
 165                 let mut first = true;
 166                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 167
 168                 if let Some(variant) = variant {
 169                     write!(f, "{}", variant.name)?;
 170
 171                     // Only for TyAdt we can have `S {...}`,
 172                     // which we handle separately here.
 173                     if variant.ctor_kind == CtorKind::Fictive {
 174                         write!(f, " {{ ")?;
 175
 176                         let mut printed = 0;
 177                         for p in subpatterns {
 178                             if let PatternKind::Wild = *p.pattern.kind {
 179                                 continue;
 180                             }
 181                             let name = variant.fields[p.field.index()].name;
 182                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 183                             printed += 1;
 184                         }
 185
 186                         if printed < variant.fields.len() {
 187                             write!(f, "{}..", start_or_continue())?;
 188                         }
 189
 190                         return write!(f, " }}");
 191                     }
 192                 }
 193
 194                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 195                 if num_fields != 0 || variant.is_none() {
 196                     write!(f, "(")?;
 197                     for i in 0..num_fields {
 198                         write!(f, "{}", start_or_continue())?;
 199
 200                         // Common case: the field is where we expect it.
 201                         if let Some(p) = subpatterns.get(i) {
 202                             if p.field.index() == i {
 203                                 write!(f, "{}", p.pattern)?;
 204                                 continue;
 205                             }
 206                         }
 207
 208                         // Otherwise, we have to go looking for it.
 209                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 210                             write!(f, "{}", p.pattern)?;
 211                         } else {
 212                             write!(f, "_")?;
 213                         }
 214                     }
 215                     write!(f, ")")?;
 216                 }
 217
 218                 Ok(())
 219             }
 220             PatternKind::Deref { ref subpattern } => {
 221                 match self.ty.sty {
 222                     ty::TyAdt(def, _) if def.is_box() => write!(f, "box ")?,
 223                     ty::TyRef(_, mt) => {
 224                         write!(f, "&")?;
 225                         if mt.mutbl == hir::MutMutable {
 226                             write!(f, "mut ")?;
 227                         }
 228                     }
 229                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 230                 }
 231                 write!(f, "{}", subpattern)
 232             }
 233             PatternKind::Constant { ref value } => {
 234                 print_const_val(value, f)
 235             }
 236             PatternKind::Range { ref lo, ref hi, ref end } => {
 237                 print_const_val(lo, f)?;
 238                 match *end {
 239                     RangeEnd::Included => write!(f, "...")?,
 240                     RangeEnd::Excluded => write!(f, "..")?,
 241                 }
 242                 print_const_val(hi, f)
 243             }
 244             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 245             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 246                 let mut first = true;
 247                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 248                 write!(f, "[")?;
 249                 for p in prefix {
 250                     write!(f, "{}{}", start_or_continue(), p)?;
 251                 }
 252                 if let Some(ref slice) = *slice {
 253                     write!(f, "{}", start_or_continue())?;
 254                     match *slice.kind {
 255                         PatternKind::Wild => {}
 256                         _ => write!(f, "{}", slice)?
 257                     }
 258                     write!(f, "..")?;
 259                 }
 260                 for p in suffix {
 261                     write!(f, "{}{}", start_or_continue(), p)?;
 262                 }
 263                 write!(f, "]")
 264             }
 265         }
 266     }
 267 }
 268
 269 pub struct PatternContext<'a, 'gcx: 'tcx, 'tcx: 'a> {
 270     pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
 271     pub tables: &'a ty::TypeckTables<'gcx>,
 272     pub errors: Vec<PatternError<'tcx>>,
 273 }
 274
 275 impl<'a, 'gcx, 'tcx> Pattern<'tcx> {
 276     pub fn from_hir(tcx: TyCtxt<'a, 'gcx, 'tcx>,
 277                     tables: &'a ty::TypeckTables<'gcx>,
 278                     pat: &hir::Pat) -> Self {
 279         let mut pcx = PatternContext::new(tcx, tables);
 280         let result = pcx.lower_pattern(pat);
 281         if !pcx.errors.is_empty() {
 282             span_bug!(pat.span, "encountered errors lowering pattern: {:?}", pcx.errors)
 283         }
 284         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 285         result
 286     }
 287 }
 288
 289 impl<'a, 'gcx, 'tcx> PatternContext<'a, 'gcx, 'tcx> {
 290     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, tables: &'a ty::TypeckTables<'gcx>) -> Self {
 291         PatternContext { tcx: tcx, tables: tables, errors: vec![] }
 292     }
 293
 294     pub fn lower_pattern(&mut self, pat: &hir::Pat) -> Pattern<'tcx> {
 295         let mut ty = self.tables.node_id_to_type(pat.id);
 296
 297         let kind = match pat.node {
 298             PatKind::Wild => PatternKind::Wild,
 299
 300             PatKind::Lit(ref value) => self.lower_lit(value),
 301
 302             PatKind::Range(ref lo, ref hi, ref end) => {
 303                 match (self.lower_lit(lo), self.lower_lit(hi)) {
 304                     (PatternKind::Constant { value: lo },
 305                      PatternKind::Constant { value: hi }) => {
 306                         PatternKind::Range { lo: lo, hi: hi, end: end.clone() }
 307                     }
 308                     _ => PatternKind::Wild
 309                 }
 310             }
 311
 312             PatKind::Path(ref qpath) => {
 313                 return self.lower_path(qpath, pat.id, pat.id, pat.span);
 314             }
 315
 316             PatKind::Ref(ref subpattern, _) |
 317             PatKind::Box(ref subpattern) => {
 318                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 319             }
 320
 321             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 322                 let ty = self.tables.node_id_to_type(pat.id);
 323                 match ty.sty {
 324                     ty::TyRef(_, mt) =>
 325                         PatternKind::Deref {
 326                             subpattern: Pattern {
 327                                 ty: mt.ty,
 328                                 span: pat.span,
 329                                 kind: Box::new(self.slice_or_array_pattern(
 330                                     pat.span, mt.ty, prefix, slice, suffix))
 331                             },
 332                         },
 333
 334                     ty::TySlice(..) |
 335                     ty::TyArray(..) =>
 336                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 337
 338                     ref sty =>
 339                         span_bug!(
 340                             pat.span,
 341                             "unexpanded type for vector pattern: {:?}",
 342                             sty),
 343                 }
 344             }
 345
 346             PatKind::Tuple(ref subpatterns, ddpos) => {
 347                 let ty = self.tables.node_id_to_type(pat.id);
 348                 match ty.sty {
 349                     ty::TyTuple(ref tys, _) => {
 350                         let subpatterns =
 351                             subpatterns.iter()
 352                                        .enumerate_and_adjust(tys.len(), ddpos)
 353                                        .map(|(i, subpattern)| FieldPattern {
 354                                             field: Field::new(i),
 355                                             pattern: self.lower_pattern(subpattern)
 356                                        })
 357                                        .collect();
 358
 359                         PatternKind::Leaf { subpatterns: subpatterns }
 360                     }
 361
 362                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 363                 }
 364             }
 365
 366             PatKind::Binding(bm, def_id, ref ident, ref sub) => {
 367                 let id = self.tcx.hir.as_local_node_id(def_id).unwrap();
 368                 let var_ty = self.tables.node_id_to_type(pat.id);
 369                 let region = match var_ty.sty {
 370                     ty::TyRef(r, _) => Some(r),
 371                     _ => None,
 372                 };
 373                 let (mutability, mode) = match bm {
 374                     hir::BindByValue(hir::MutMutable) =>
 375                         (Mutability::Mut, BindingMode::ByValue),
 376                     hir::BindByValue(hir::MutImmutable) =>
 377                         (Mutability::Not, BindingMode::ByValue),
 378                     hir::BindByRef(hir::MutMutable) =>
 379                         (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Mut)),
 380                     hir::BindByRef(hir::MutImmutable) =>
 381                         (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Shared)),
 382                 };
 383
 384                 // A ref x pattern is the same node used for x, and as such it has
 385                 // x's type, which is &T, where we want T (the type being matched).
 386                 if let hir::BindByRef(_) = bm {
 387                     if let ty::TyRef(_, mt) = ty.sty {
 388                         ty = mt.ty;
 389                     } else {
 390                         bug!("`ref {}` has wrong type {}", ident.node, ty);
 391                     }
 392                 }
 393
 394                 PatternKind::Binding {
 395                     mutability: mutability,
 396                     mode: mode,
 397                     name: ident.node,
 398                     var: id,
 399                     ty: var_ty,
 400                     subpattern: self.lower_opt_pattern(sub),
 401                 }
 402             }
 403
 404             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 405                 let def = self.tables.qpath_def(qpath, pat.id);
 406                 let adt_def = match ty.sty {
 407                     ty::TyAdt(adt_def, _) => adt_def,
 408                     _ => span_bug!(pat.span, "tuple struct pattern not applied to an ADT"),
 409                 };
 410                 let variant_def = adt_def.variant_of_def(def);
 411
 412                 let subpatterns =
 413                         subpatterns.iter()
 414                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 415                                    .map(|(i, field)| FieldPattern {
 416                                        field: Field::new(i),
 417                                        pattern: self.lower_pattern(field),
 418                                    })
 419                                    .collect();
 420                 self.lower_variant_or_leaf(def, ty, subpatterns)
 421             }
 422
 423             PatKind::Struct(ref qpath, ref fields, _) => {
 424                 let def = self.tables.qpath_def(qpath, pat.id);
 425                 let adt_def = match ty.sty {
 426                     ty::TyAdt(adt_def, _) => adt_def,
 427                     _ => {
 428                         span_bug!(
 429                             pat.span,
 430                             "struct pattern not applied to an ADT");
 431                     }
 432                 };
 433                 let variant_def = adt_def.variant_of_def(def);
 434
 435                 let subpatterns =
 436                     fields.iter()
 437                           .map(|field| {
 438                               let index = variant_def.index_of_field_named(field.node.name);
 439                               let index = index.unwrap_or_else(|| {
 440                                   span_bug!(
 441                                       pat.span,
 442                                       "no field with name {:?}",
 443                                       field.node.name);
 444                               });
 445                               FieldPattern {
 446                                   field: Field::new(index),
 447                                   pattern: self.lower_pattern(&field.node.pat),
 448                               }
 449                           })
 450                           .collect();
 451
 452                 self.lower_variant_or_leaf(def, ty, subpatterns)
 453             }
 454         };
 455
 456         Pattern {
 457             span: pat.span,
 458             ty: ty,
 459             kind: Box::new(kind),
 460         }
 461     }
 462
 463     fn lower_patterns(&mut self, pats: &[P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 464         pats.iter().map(|p| self.lower_pattern(p)).collect()
 465     }
 466
 467     fn lower_opt_pattern(&mut self, pat: &Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 468     {
 469         pat.as_ref().map(|p| self.lower_pattern(p))
 470     }
 471
 472     fn flatten_nested_slice_patterns(
 473         &mut self,
 474         prefix: Vec<Pattern<'tcx>>,
 475         slice: Option<Pattern<'tcx>>,
 476         suffix: Vec<Pattern<'tcx>>)
 477         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 478     {
 479         let orig_slice = match slice {
 480             Some(orig_slice) => orig_slice,
 481             None => return (prefix, slice, suffix)
 482         };
 483         let orig_prefix = prefix;
 484         let orig_suffix = suffix;
 485
 486         // dance because of intentional borrow-checker stupidity.
 487         let kind = *orig_slice.kind;
 488         match kind {
 489             PatternKind::Slice { prefix, slice, mut suffix } |
 490             PatternKind::Array { prefix, slice, mut suffix } => {
 491                 let mut orig_prefix = orig_prefix;
 492
 493                 orig_prefix.extend(prefix);
 494                 suffix.extend(orig_suffix);
 495
 496                 (orig_prefix, slice, suffix)
 497             }
 498             _ => {
 499                 (orig_prefix, Some(Pattern {
 500                     kind: box kind, ..orig_slice
 501                 }), orig_suffix)
 502             }
 503         }
 504     }
 505
 506     fn slice_or_array_pattern(
 507         &mut self,
 508         span: Span,
 509         ty: Ty<'tcx>,
 510         prefix: &[P<hir::Pat>],
 511         slice: &Option<P<hir::Pat>>,
 512         suffix: &[P<hir::Pat>])
 513         -> PatternKind<'tcx>
 514     {
 515         let prefix = self.lower_patterns(prefix);
 516         let slice = self.lower_opt_pattern(slice);
 517         let suffix = self.lower_patterns(suffix);
 518         let (prefix, slice, suffix) =
 519             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 520
 521         match ty.sty {
 522             ty::TySlice(..) => {
 523                 // matching a slice or fixed-length array
 524                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 525             }
 526
 527             ty::TyArray(_, len) => {
 528                 // fixed-length array
 529                 assert!(len >= prefix.len() + suffix.len());
 530                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 531             }
 532
 533             _ => {
 534                 span_bug!(span, "bad slice pattern type {:?}", ty);
 535             }
 536         }
 537     }
 538
 539     fn lower_variant_or_leaf(
 540         &mut self,
 541         def: Def,
 542         ty: Ty<'tcx>,
 543         subpatterns: Vec<FieldPattern<'tcx>>)
 544         -> PatternKind<'tcx>
 545     {
 546         match def {
 547             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 548                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 549                 let adt_def = self.tcx.lookup_adt_def(enum_id);
 550                 if adt_def.variants.len() > 1 {
 551                     let substs = match ty.sty {
 552                         TypeVariants::TyAdt(_, substs) => substs,
 553                         TypeVariants::TyFnDef(_, substs, _) => substs,
 554                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 555                     };
 556                     PatternKind::Variant {
 557                         adt_def: adt_def,
 558                         substs: substs,
 559                         variant_index: adt_def.variant_index_with_id(variant_id),
 560                         subpatterns: subpatterns,
 561                     }
 562                 } else {
 563                     PatternKind::Leaf { subpatterns: subpatterns }
 564                 }
 565             }
 566
 567             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 568             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 569                 PatternKind::Leaf { subpatterns: subpatterns }
 570             }
 571
 572             _ => bug!()
 573         }
 574     }
 575
 576     fn lower_path(&mut self,
 577                   qpath: &hir::QPath,
 578                   id: ast::NodeId,
 579                   pat_id: ast::NodeId,
 580                   span: Span)
 581                   -> Pattern<'tcx> {
 582         let ty = self.tables.node_id_to_type(id);
 583         let def = self.tables.qpath_def(qpath, id);
 584         let kind = match def {
 585             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 586                 let tcx = self.tcx.global_tcx();
 587                 let substs = self.tables.node_id_item_substs(id)
 588                     .unwrap_or_else(|| tcx.intern_substs(&[]));
 589                 match eval::lookup_const_by_id(tcx, def_id, substs) {
 590                     Some((const_expr, const_tables)) => {
 591                         // Enter the inlined constant's tables temporarily.
 592                         let old_tables = self.tables;
 593                         self.tables = const_tables;
 594                         let pat = self.lower_const_expr(const_expr, pat_id, span);
 595                         self.tables = old_tables;
 596                         return pat;
 597                     }
 598                     None => {
 599                         self.errors.push(PatternError::StaticInPattern(span));
 600                         PatternKind::Wild
 601                     }
 602                 }
 603             }
 604             _ => self.lower_variant_or_leaf(def, ty, vec![]),
 605         };
 606
 607         Pattern {
 608             span: span,
 609             ty: ty,
 610             kind: Box::new(kind),
 611         }
 612     }
 613
 614     fn lower_lit(&mut self, expr: &hir::Expr) -> PatternKind<'tcx> {
 615         let const_cx = eval::ConstContext::with_tables(self.tcx.global_tcx(), self.tables);
 616         match const_cx.eval(expr) {
 617             Ok(value) => {
 618                 PatternKind::Constant { value: value }
 619             }
 620             Err(e) => {
 621                 self.errors.push(PatternError::ConstEval(e));
 622                 PatternKind::Wild
 623             }
 624         }
 625     }
 626
 627     fn lower_const_expr(&mut self,
 628                         expr: &hir::Expr,
 629                         pat_id: ast::NodeId,
 630                         span: Span)
 631                         -> Pattern<'tcx> {
 632         let pat_ty = self.tables.expr_ty(expr);
 633         debug!("expr={:?} pat_ty={:?} pat_id={}", expr, pat_ty, pat_id);
 634         match pat_ty.sty {
 635             ty::TyFloat(_) => {
 636                 self.tcx.sess.add_lint(
 637                     lint::builtin::ILLEGAL_FLOATING_POINT_CONSTANT_PATTERN,
 638                     pat_id,
 639                     span,
 640                     format!("floating point constants cannot be used in patterns"));
 641             }
 642             ty::TyAdt(adt_def, _) if adt_def.is_union() => {
 643                 // Matching on union fields is unsafe, we can't hide it in constants
 644                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 645             }
 646             ty::TyAdt(adt_def, _) => {
 647                 if !self.tcx.has_attr(adt_def.did, "structural_match") {
 648                     self.tcx.sess.add_lint(
 649                         lint::builtin::ILLEGAL_STRUCT_OR_ENUM_CONSTANT_PATTERN,
 650                         pat_id,
 651                         span,
 652                         format!("to use a constant of type `{}` \
 653                                  in a pattern, \
 654                                  `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 655                                 self.tcx.item_path_str(adt_def.did),
 656                                 self.tcx.item_path_str(adt_def.did)));
 657                 }
 658             }
 659             _ => { }
 660         }
 661         let kind = match expr.node {
 662             hir::ExprTup(ref exprs) => {
 663                 PatternKind::Leaf {
 664                     subpatterns: exprs.iter().enumerate().map(|(i, expr)| {
 665                         FieldPattern {
 666                             field: Field::new(i),
 667                             pattern: self.lower_const_expr(expr, pat_id, span)
 668                         }
 669                     }).collect()
 670                 }
 671             }
 672
 673             hir::ExprCall(ref callee, ref args) => {
 674                 let qpath = match callee.node {
 675                     hir::ExprPath(ref qpath) => qpath,
 676                     _ => bug!()
 677                 };
 678                 let ty = self.tables.node_id_to_type(callee.id);
 679                 let def = self.tables.qpath_def(qpath, callee.id);
 680                 match def {
 681                     Def::Fn(..) | Def::Method(..) => self.lower_lit(expr),
 682                     _ => {
 683                         let subpatterns = args.iter().enumerate().map(|(i, expr)| {
 684                             FieldPattern {
 685                                 field: Field::new(i),
 686                                 pattern: self.lower_const_expr(expr, pat_id, span)
 687                             }
 688                         }).collect();
 689                         self.lower_variant_or_leaf(def, ty, subpatterns)
 690                     }
 691                 }
 692             }
 693
 694             hir::ExprStruct(ref qpath, ref fields, None) => {
 695                 let def = self.tables.qpath_def(qpath, expr.id);
 696                 let adt_def = match pat_ty.sty {
 697                     ty::TyAdt(adt_def, _) => adt_def,
 698                     _ => {
 699                         span_bug!(
 700                             expr.span,
 701                             "struct expr without ADT type");
 702                     }
 703                 };
 704                 let variant_def = adt_def.variant_of_def(def);
 705
 706                 let subpatterns =
 707                     fields.iter()
 708                           .map(|field| {
 709                               let index = variant_def.index_of_field_named(field.name.node);
 710                               let index = index.unwrap_or_else(|| {
 711                                   span_bug!(
 712                                       expr.span,
 713                                       "no field with name {:?}",
 714                                       field.name);
 715                               });
 716                               FieldPattern {
 717                                   field: Field::new(index),
 718                                   pattern: self.lower_const_expr(&field.expr, pat_id, span),
 719                               }
 720                           })
 721                           .collect();
 722
 723                 self.lower_variant_or_leaf(def, pat_ty, subpatterns)
 724             }
 725
 726             hir::ExprArray(ref exprs) => {
 727                 let pats = exprs.iter()
 728                                 .map(|expr| self.lower_const_expr(expr, pat_id, span))
 729                                 .collect();
 730                 PatternKind::Array {
 731                     prefix: pats,
 732                     slice: None,
 733                     suffix: vec![]
 734                 }
 735             }
 736
 737             hir::ExprPath(ref qpath) => {
 738                 return self.lower_path(qpath, expr.id, pat_id, span);
 739             }
 740
 741             _ => self.lower_lit(expr)
 742         };
 743
 744         Pattern {
 745             span: span,
 746             ty: pat_ty,
 747             kind: Box::new(kind),
 748         }
 749     }
 750 }
 751
 752 pub trait PatternFoldable<'tcx> : Sized {
 753     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 754         self.super_fold_with(folder)
 755     }
 756
 757     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
 758 }
 759
 760 pub trait PatternFolder<'tcx> : Sized {
 761     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
 762         pattern.super_fold_with(self)
 763     }
 764
 765     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
 766         kind.super_fold_with(self)
 767     }
 768 }
 769
 770
 771 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
 772     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 773         let content: T = (**self).fold_with(folder);
 774         box content
 775     }
 776 }
 777
 778 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
 779     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 780         self.iter().map(|t| t.fold_with(folder)).collect()
 781     }
 782 }
 783
 784 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
 785     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
 786         self.as_ref().map(|t| t.fold_with(folder))
 787     }
 788 }
 789
 790 macro_rules! CloneImpls {
 791     (<$lt_tcx:tt> $($ty:ty),+) => {
 792         $(
 793             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
 794                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
 795                     Clone::clone(self)
 796                 }
 797             }
 798         )+
 799     }
 800 }
 801
 802 CloneImpls!{ <'tcx>
 803     Span, Field, Mutability, ast::Name, ast::NodeId, usize, ConstVal<'tcx>, Region,
 804     Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
 805     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>
 806 }
 807
 808 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
 809     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 810         FieldPattern {
 811             field: self.field.fold_with(folder),
 812             pattern: self.pattern.fold_with(folder)
 813         }
 814     }
 815 }
 816
 817 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
 818     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 819         folder.fold_pattern(self)
 820     }
 821
 822     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 823         Pattern {
 824             ty: self.ty.fold_with(folder),
 825             span: self.span.fold_with(folder),
 826             kind: self.kind.fold_with(folder)
 827         }
 828     }
 829 }
 830
 831 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
 832     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 833         folder.fold_pattern_kind(self)
 834     }
 835
 836     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 837         match *self {
 838             PatternKind::Wild => PatternKind::Wild,
 839             PatternKind::Binding {
 840                 mutability,
 841                 name,
 842                 mode,
 843                 var,
 844                 ty,
 845                 ref subpattern,
 846             } => PatternKind::Binding {
 847                 mutability: mutability.fold_with(folder),
 848                 name: name.fold_with(folder),
 849                 mode: mode.fold_with(folder),
 850                 var: var.fold_with(folder),
 851                 ty: ty.fold_with(folder),
 852                 subpattern: subpattern.fold_with(folder),
 853             },
 854             PatternKind::Variant {
 855                 adt_def,
 856                 substs,
 857                 variant_index,
 858                 ref subpatterns,
 859             } => PatternKind::Variant {
 860                 adt_def: adt_def.fold_with(folder),
 861                 substs: substs.fold_with(folder),
 862                 variant_index: variant_index.fold_with(folder),
 863                 subpatterns: subpatterns.fold_with(folder)
 864             },
 865             PatternKind::Leaf {
 866                 ref subpatterns,
 867             } => PatternKind::Leaf {
 868                 subpatterns: subpatterns.fold_with(folder),
 869             },
 870             PatternKind::Deref {
 871                 ref subpattern,
 872             } => PatternKind::Deref {
 873                 subpattern: subpattern.fold_with(folder),
 874             },
 875             PatternKind::Constant {
 876                 ref value
 877             } => PatternKind::Constant {
 878                 value: value.fold_with(folder)
 879             },
 880             PatternKind::Range {
 881                 ref lo,
 882                 ref hi,
 883                 ref end,
 884             } => PatternKind::Range {
 885                 lo: lo.fold_with(folder),
 886                 hi: hi.fold_with(folder),
 887                 end: end.clone(),
 888             },
 889             PatternKind::Slice {
 890                 ref prefix,
 891                 ref slice,
 892                 ref suffix,
 893             } => PatternKind::Slice {
 894                 prefix: prefix.fold_with(folder),
 895                 slice: slice.fold_with(folder),
 896                 suffix: suffix.fold_with(folder)
 897             },
 898             PatternKind::Array {
 899                 ref prefix,
 900                 ref slice,
 901                 ref suffix
 902             } => PatternKind::Array {
 903                 prefix: prefix.fold_with(folder),
 904                 slice: slice.fold_with(folder),
 905                 suffix: suffix.fold_with(folder)
 906             },
 907         }
 908     }
 909 }