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::middle::const_val::{ConstEvalErr, ConstVal};
  14 use rustc::mir::{Field, BorrowKind, Mutability};
  15 use rustc::ty::{self, TyCtxt, AdtDef, Ty, Region};
  16 use rustc::ty::subst::{Substs, Kind};
  17 use rustc::hir::{self, PatKind, RangeEnd};
  18 use rustc::hir::def::{Def, CtorKind};
  19 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  20
  21 use rustc_data_structures::indexed_vec::Idx;
  22
  23 use std::fmt;
  24 use syntax::ast;
  25 use syntax::ptr::P;
  26 use syntax_pos::Span;
  27
  28 #[derive(Clone, Debug)]
  29 pub enum PatternError<'tcx> {
  30     StaticInPattern(Span),
  31     ConstEval(ConstEvalErr<'tcx>),
  32 }
  33
  34 #[derive(Copy, Clone, Debug)]
  35 pub enum BindingMode<'tcx> {
  36     ByValue,
  37     ByRef(Region<'tcx>, BorrowKind),
  38 }
  39
  40 #[derive(Clone, Debug)]
  41 pub struct FieldPattern<'tcx> {
  42     pub field: Field,
  43     pub pattern: Pattern<'tcx>,
  44 }
  45
  46 #[derive(Clone, Debug)]
  47 pub struct Pattern<'tcx> {
  48     pub ty: Ty<'tcx>,
  49     pub span: Span,
  50     pub kind: Box<PatternKind<'tcx>>,
  51 }
  52
  53 #[derive(Clone, Debug)]
  54 pub enum PatternKind<'tcx> {
  55     Wild,
  56
  57     /// x, ref x, x @ P, etc
  58     Binding {
  59         mutability: Mutability,
  60         name: ast::Name,
  61         mode: BindingMode<'tcx>,
  62         var: ast::NodeId,
  63         ty: Ty<'tcx>,
  64         subpattern: Option<Pattern<'tcx>>,
  65     },
  66
  67     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
  68     Variant {
  69         adt_def: &'tcx AdtDef,
  70         substs: &'tcx Substs<'tcx>,
  71         variant_index: usize,
  72         subpatterns: Vec<FieldPattern<'tcx>>,
  73     },
  74
  75     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
  76     Leaf {
  77         subpatterns: Vec<FieldPattern<'tcx>>,
  78     },
  79
  80     /// box P, &P, &mut P, etc
  81     Deref {
  82         subpattern: Pattern<'tcx>,
  83     },
  84
  85     Constant {
  86         value: ConstVal<'tcx>,
  87     },
  88
  89     Range {
  90         lo: ConstVal<'tcx>,
  91         hi: ConstVal<'tcx>,
  92         end: RangeEnd,
  93     },
  94
  95     /// matches against a slice, checking the length and extracting elements
  96     Slice {
  97         prefix: Vec<Pattern<'tcx>>,
  98         slice: Option<Pattern<'tcx>>,
  99         suffix: Vec<Pattern<'tcx>>,
 100     },
 101
 102     /// fixed match against an array, irrefutable
 103     Array {
 104         prefix: Vec<Pattern<'tcx>>,
 105         slice: Option<Pattern<'tcx>>,
 106         suffix: Vec<Pattern<'tcx>>,
 107     },
 108 }
 109
 110 fn print_const_val(value: &ConstVal, f: &mut fmt::Formatter) -> fmt::Result {
 111     match *value {
 112         ConstVal::Float(ref x) => write!(f, "{}", x),
 113         ConstVal::Integral(ref i) => write!(f, "{}", i),
 114         ConstVal::Str(ref s) => write!(f, "{:?}", &s[..]),
 115         ConstVal::ByteStr(ref b) => write!(f, "{:?}", &b[..]),
 116         ConstVal::Bool(b) => write!(f, "{:?}", b),
 117         ConstVal::Char(c) => write!(f, "{:?}", c),
 118         ConstVal::Variant(_) |
 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, 'tcx: 'a> {
 270     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 271     pub param_env: ty::ParamEnv<'tcx>,
 272     pub tables: &'a ty::TypeckTables<'tcx>,
 273     pub substs: &'tcx Substs<'tcx>,
 274     pub errors: Vec<PatternError<'tcx>>,
 275 }
 276
 277 impl<'a, 'tcx> Pattern<'tcx> {
 278     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 279                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 280                     tables: &'a ty::TypeckTables<'tcx>,
 281                     pat: &hir::Pat) -> Self {
 282         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 283         let result = pcx.lower_pattern(pat);
 284         if !pcx.errors.is_empty() {
 285             span_bug!(pat.span, "encountered errors lowering pattern: {:?}", pcx.errors)
 286         }
 287         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 288         result
 289     }
 290 }
 291
 292 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 293     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 294                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 295                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 296         PatternContext {
 297             tcx,
 298             param_env: param_env_and_substs.param_env,
 299             tables,
 300             substs: param_env_and_substs.value,
 301             errors: vec![]
 302         }
 303     }
 304
 305     pub fn lower_pattern(&mut self, pat: &hir::Pat) -> Pattern<'tcx> {
 306         let mut ty = self.tables.node_id_to_type(pat.id);
 307
 308         let kind = match pat.node {
 309             PatKind::Wild => PatternKind::Wild,
 310
 311             PatKind::Lit(ref value) => self.lower_lit(value),
 312
 313             PatKind::Range(ref lo, ref hi, ref end) => {
 314                 match (self.lower_lit(lo), self.lower_lit(hi)) {
 315                     (PatternKind::Constant { value: lo },
 316                      PatternKind::Constant { value: hi }) => {
 317                         PatternKind::Range { lo: lo, hi: hi, end: end.clone() }
 318                     }
 319                     _ => PatternKind::Wild
 320                 }
 321             }
 322
 323             PatKind::Path(ref qpath) => {
 324                 return self.lower_path(qpath, pat.id, pat.id, pat.span);
 325             }
 326
 327             PatKind::Ref(ref subpattern, _) |
 328             PatKind::Box(ref subpattern) => {
 329                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 330             }
 331
 332             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 333                 let ty = self.tables.node_id_to_type(pat.id);
 334                 match ty.sty {
 335                     ty::TyRef(_, mt) =>
 336                         PatternKind::Deref {
 337                             subpattern: Pattern {
 338                                 ty: mt.ty,
 339                                 span: pat.span,
 340                                 kind: Box::new(self.slice_or_array_pattern(
 341                                     pat.span, mt.ty, prefix, slice, suffix))
 342                             },
 343                         },
 344
 345                     ty::TySlice(..) |
 346                     ty::TyArray(..) =>
 347                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 348
 349                     ref sty =>
 350                         span_bug!(
 351                             pat.span,
 352                             "unexpanded type for vector pattern: {:?}",
 353                             sty),
 354                 }
 355             }
 356
 357             PatKind::Tuple(ref subpatterns, ddpos) => {
 358                 let ty = self.tables.node_id_to_type(pat.id);
 359                 match ty.sty {
 360                     ty::TyTuple(ref tys, _) => {
 361                         let subpatterns =
 362                             subpatterns.iter()
 363                                        .enumerate_and_adjust(tys.len(), ddpos)
 364                                        .map(|(i, subpattern)| FieldPattern {
 365                                             field: Field::new(i),
 366                                             pattern: self.lower_pattern(subpattern)
 367                                        })
 368                                        .collect();
 369
 370                         PatternKind::Leaf { subpatterns: subpatterns }
 371                     }
 372
 373                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 374                 }
 375             }
 376
 377             PatKind::Binding(bm, def_id, ref ident, ref sub) => {
 378                 let id = self.tcx.hir.as_local_node_id(def_id).unwrap();
 379                 let var_ty = self.tables.node_id_to_type(pat.id);
 380                 let region = match var_ty.sty {
 381                     ty::TyRef(r, _) => Some(r),
 382                     _ => None,
 383                 };
 384                 let (mutability, mode) = match bm {
 385                     hir::BindByValue(hir::MutMutable) =>
 386                         (Mutability::Mut, BindingMode::ByValue),
 387                     hir::BindByValue(hir::MutImmutable) =>
 388                         (Mutability::Not, BindingMode::ByValue),
 389                     hir::BindByRef(hir::MutMutable) =>
 390                         (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Mut)),
 391                     hir::BindByRef(hir::MutImmutable) =>
 392                         (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Shared)),
 393                 };
 394
 395                 // A ref x pattern is the same node used for x, and as such it has
 396                 // x's type, which is &T, where we want T (the type being matched).
 397                 if let hir::BindByRef(_) = bm {
 398                     if let ty::TyRef(_, mt) = ty.sty {
 399                         ty = mt.ty;
 400                     } else {
 401                         bug!("`ref {}` has wrong type {}", ident.node, ty);
 402                     }
 403                 }
 404
 405                 PatternKind::Binding {
 406                     mutability: mutability,
 407                     mode: mode,
 408                     name: ident.node,
 409                     var: id,
 410                     ty: var_ty,
 411                     subpattern: self.lower_opt_pattern(sub),
 412                 }
 413             }
 414
 415             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 416                 let def = self.tables.qpath_def(qpath, pat.id);
 417                 let adt_def = match ty.sty {
 418                     ty::TyAdt(adt_def, _) => adt_def,
 419                     _ => span_bug!(pat.span, "tuple struct pattern not applied to an ADT"),
 420                 };
 421                 let variant_def = adt_def.variant_of_def(def);
 422
 423                 let subpatterns =
 424                         subpatterns.iter()
 425                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 426                                    .map(|(i, field)| FieldPattern {
 427                                        field: Field::new(i),
 428                                        pattern: self.lower_pattern(field),
 429                                    })
 430                                    .collect();
 431                 self.lower_variant_or_leaf(def, ty, subpatterns)
 432             }
 433
 434             PatKind::Struct(ref qpath, ref fields, _) => {
 435                 let def = self.tables.qpath_def(qpath, pat.id);
 436                 let adt_def = match ty.sty {
 437                     ty::TyAdt(adt_def, _) => adt_def,
 438                     _ => {
 439                         span_bug!(
 440                             pat.span,
 441                             "struct pattern not applied to an ADT");
 442                     }
 443                 };
 444                 let variant_def = adt_def.variant_of_def(def);
 445
 446                 let subpatterns =
 447                     fields.iter()
 448                           .map(|field| {
 449                               let index = variant_def.index_of_field_named(field.node.name);
 450                               let index = index.unwrap_or_else(|| {
 451                                   span_bug!(
 452                                       pat.span,
 453                                       "no field with name {:?}",
 454                                       field.node.name);
 455                               });
 456                               FieldPattern {
 457                                   field: Field::new(index),
 458                                   pattern: self.lower_pattern(&field.node.pat),
 459                               }
 460                           })
 461                           .collect();
 462
 463                 self.lower_variant_or_leaf(def, ty, subpatterns)
 464             }
 465         };
 466
 467         Pattern {
 468             span: pat.span,
 469             ty: ty,
 470             kind: Box::new(kind),
 471         }
 472     }
 473
 474     fn lower_patterns(&mut self, pats: &[P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 475         pats.iter().map(|p| self.lower_pattern(p)).collect()
 476     }
 477
 478     fn lower_opt_pattern(&mut self, pat: &Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 479     {
 480         pat.as_ref().map(|p| self.lower_pattern(p))
 481     }
 482
 483     fn flatten_nested_slice_patterns(
 484         &mut self,
 485         prefix: Vec<Pattern<'tcx>>,
 486         slice: Option<Pattern<'tcx>>,
 487         suffix: Vec<Pattern<'tcx>>)
 488         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 489     {
 490         let orig_slice = match slice {
 491             Some(orig_slice) => orig_slice,
 492             None => return (prefix, slice, suffix)
 493         };
 494         let orig_prefix = prefix;
 495         let orig_suffix = suffix;
 496
 497         // dance because of intentional borrow-checker stupidity.
 498         let kind = *orig_slice.kind;
 499         match kind {
 500             PatternKind::Slice { prefix, slice, mut suffix } |
 501             PatternKind::Array { prefix, slice, mut suffix } => {
 502                 let mut orig_prefix = orig_prefix;
 503
 504                 orig_prefix.extend(prefix);
 505                 suffix.extend(orig_suffix);
 506
 507                 (orig_prefix, slice, suffix)
 508             }
 509             _ => {
 510                 (orig_prefix, Some(Pattern {
 511                     kind: box kind, ..orig_slice
 512                 }), orig_suffix)
 513             }
 514         }
 515     }
 516
 517     fn slice_or_array_pattern(
 518         &mut self,
 519         span: Span,
 520         ty: Ty<'tcx>,
 521         prefix: &[P<hir::Pat>],
 522         slice: &Option<P<hir::Pat>>,
 523         suffix: &[P<hir::Pat>])
 524         -> PatternKind<'tcx>
 525     {
 526         let prefix = self.lower_patterns(prefix);
 527         let slice = self.lower_opt_pattern(slice);
 528         let suffix = self.lower_patterns(suffix);
 529         let (prefix, slice, suffix) =
 530             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 531
 532         match ty.sty {
 533             ty::TySlice(..) => {
 534                 // matching a slice or fixed-length array
 535                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 536             }
 537
 538             ty::TyArray(_, len) => {
 539                 // fixed-length array
 540                 assert!(len >= prefix.len() + suffix.len());
 541                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 542             }
 543
 544             _ => {
 545                 span_bug!(span, "bad slice pattern type {:?}", ty);
 546             }
 547         }
 548     }
 549
 550     fn lower_variant_or_leaf(
 551         &mut self,
 552         def: Def,
 553         ty: Ty<'tcx>,
 554         subpatterns: Vec<FieldPattern<'tcx>>)
 555         -> PatternKind<'tcx>
 556     {
 557         match def {
 558             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 559                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 560                 let adt_def = self.tcx.adt_def(enum_id);
 561                 if adt_def.variants.len() > 1 {
 562                     let substs = match ty.sty {
 563                         ty::TyAdt(_, substs) |
 564                         ty::TyFnDef(_, substs) => substs,
 565                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 566                     };
 567                     PatternKind::Variant {
 568                         adt_def: adt_def,
 569                         substs: substs,
 570                         variant_index: adt_def.variant_index_with_id(variant_id),
 571                         subpatterns: subpatterns,
 572                     }
 573                 } else {
 574                     PatternKind::Leaf { subpatterns: subpatterns }
 575                 }
 576             }
 577
 578             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 579             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
 580                 PatternKind::Leaf { subpatterns: subpatterns }
 581             }
 582
 583             _ => bug!()
 584         }
 585     }
 586
 587     fn lower_path(&mut self,
 588                   qpath: &hir::QPath,
 589                   id: ast::NodeId,
 590                   pat_id: ast::NodeId,
 591                   span: Span)
 592                   -> Pattern<'tcx> {
 593         let ty = self.tables.node_id_to_type(id);
 594         let def = self.tables.qpath_def(qpath, id);
 595         let kind = match def {
 596             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 597                 let substs = self.tables.node_substs(id);
 598                 match eval::lookup_const_by_id(self.tcx, self.param_env.and((def_id, substs))) {
 599                     Some((def_id, substs)) => {
 600                         // Enter the inlined constant's tables&substs temporarily.
 601                         let old_tables = self.tables;
 602                         let old_substs = self.substs;
 603                         self.tables = self.tcx.typeck_tables_of(def_id);
 604                         self.substs = substs;
 605                         let body = if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
 606                             self.tcx.hir.body(self.tcx.hir.body_owned_by(id))
 607                         } else {
 608                             self.tcx.sess.cstore.item_body(self.tcx, def_id)
 609                         };
 610                         let pat = self.lower_const_expr(&body.value, pat_id, span);
 611                         self.tables = old_tables;
 612                         self.substs = old_substs;
 613                         return pat;
 614                     }
 615                     None => {
 616                         self.errors.push(PatternError::StaticInPattern(span));
 617                         PatternKind::Wild
 618                     }
 619                 }
 620             }
 621             _ => self.lower_variant_or_leaf(def, ty, vec![]),
 622         };
 623
 624         Pattern {
 625             span: span,
 626             ty: ty,
 627             kind: Box::new(kind),
 628         }
 629     }
 630
 631     fn lower_lit(&mut self, expr: &hir::Expr) -> PatternKind<'tcx> {
 632         let const_cx = eval::ConstContext::new(self.tcx,
 633                                                self.param_env.and(self.substs),
 634                                                self.tables);
 635         match const_cx.eval(expr) {
 636             Ok(value) => {
 637                 if let ConstVal::Variant(def_id) = value {
 638                     let ty = self.tables.expr_ty(expr);
 639                     self.lower_variant_or_leaf(Def::Variant(def_id), ty, vec![])
 640                 } else {
 641                     PatternKind::Constant { value: value }
 642                 }
 643             }
 644             Err(e) => {
 645                 self.errors.push(PatternError::ConstEval(e));
 646                 PatternKind::Wild
 647             }
 648         }
 649     }
 650
 651     fn lower_const_expr(&mut self,
 652                         expr: &hir::Expr,
 653                         pat_id: ast::NodeId,
 654                         span: Span)
 655                         -> Pattern<'tcx> {
 656         let pat_ty = self.tables.expr_ty(expr);
 657         debug!("expr={:?} pat_ty={:?} pat_id={}", expr, pat_ty, pat_id);
 658         match pat_ty.sty {
 659             ty::TyFloat(_) => {
 660                 self.tcx.sess.span_err(span, "floating point constants cannot be used in patterns");
 661             }
 662             ty::TyAdt(adt_def, _) if adt_def.is_union() => {
 663                 // Matching on union fields is unsafe, we can't hide it in constants
 664                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 665             }
 666             ty::TyAdt(adt_def, _) => {
 667                 if !self.tcx.has_attr(adt_def.did, "structural_match") {
 668                     let msg = format!("to use a constant of type `{}` in a pattern, \
 669                                        `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 670                                       self.tcx.item_path_str(adt_def.did),
 671                                       self.tcx.item_path_str(adt_def.did));
 672                     self.tcx.sess.span_err(span, &msg);
 673                 }
 674             }
 675             _ => { }
 676         }
 677         let kind = match expr.node {
 678             hir::ExprTup(ref exprs) => {
 679                 PatternKind::Leaf {
 680                     subpatterns: exprs.iter().enumerate().map(|(i, expr)| {
 681                         FieldPattern {
 682                             field: Field::new(i),
 683                             pattern: self.lower_const_expr(expr, pat_id, span)
 684                         }
 685                     }).collect()
 686                 }
 687             }
 688
 689             hir::ExprCall(ref callee, ref args) => {
 690                 let qpath = match callee.node {
 691                     hir::ExprPath(ref qpath) => qpath,
 692                     _ => bug!()
 693                 };
 694                 let ty = self.tables.node_id_to_type(callee.id);
 695                 let def = self.tables.qpath_def(qpath, callee.id);
 696                 match def {
 697                     Def::Fn(..) | Def::Method(..) => self.lower_lit(expr),
 698                     _ => {
 699                         let subpatterns = args.iter().enumerate().map(|(i, expr)| {
 700                             FieldPattern {
 701                                 field: Field::new(i),
 702                                 pattern: self.lower_const_expr(expr, pat_id, span)
 703                             }
 704                         }).collect();
 705                         self.lower_variant_or_leaf(def, ty, subpatterns)
 706                     }
 707                 }
 708             }
 709
 710             hir::ExprStruct(ref qpath, ref fields, None) => {
 711                 let def = self.tables.qpath_def(qpath, expr.id);
 712                 let adt_def = match pat_ty.sty {
 713                     ty::TyAdt(adt_def, _) => adt_def,
 714                     _ => {
 715                         span_bug!(
 716                             expr.span,
 717                             "struct expr without ADT type");
 718                     }
 719                 };
 720                 let variant_def = adt_def.variant_of_def(def);
 721
 722                 let subpatterns =
 723                     fields.iter()
 724                           .map(|field| {
 725                               let index = variant_def.index_of_field_named(field.name.node);
 726                               let index = index.unwrap_or_else(|| {
 727                                   span_bug!(
 728                                       expr.span,
 729                                       "no field with name {:?}",
 730                                       field.name);
 731                               });
 732                               FieldPattern {
 733                                   field: Field::new(index),
 734                                   pattern: self.lower_const_expr(&field.expr, pat_id, span),
 735                               }
 736                           })
 737                           .collect();
 738
 739                 self.lower_variant_or_leaf(def, pat_ty, subpatterns)
 740             }
 741
 742             hir::ExprArray(ref exprs) => {
 743                 let pats = exprs.iter()
 744                                 .map(|expr| self.lower_const_expr(expr, pat_id, span))
 745                                 .collect();
 746                 PatternKind::Array {
 747                     prefix: pats,
 748                     slice: None,
 749                     suffix: vec![]
 750                 }
 751             }
 752
 753             hir::ExprPath(ref qpath) => {
 754                 return self.lower_path(qpath, expr.id, pat_id, span);
 755             }
 756
 757             _ => self.lower_lit(expr)
 758         };
 759
 760         Pattern {
 761             span: span,
 762             ty: pat_ty,
 763             kind: Box::new(kind),
 764         }
 765     }
 766 }
 767
 768 pub trait PatternFoldable<'tcx> : Sized {
 769     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 770         self.super_fold_with(folder)
 771     }
 772
 773     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
 774 }
 775
 776 pub trait PatternFolder<'tcx> : Sized {
 777     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
 778         pattern.super_fold_with(self)
 779     }
 780
 781     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
 782         kind.super_fold_with(self)
 783     }
 784 }
 785
 786
 787 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
 788     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 789         let content: T = (**self).fold_with(folder);
 790         box content
 791     }
 792 }
 793
 794 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
 795     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 796         self.iter().map(|t| t.fold_with(folder)).collect()
 797     }
 798 }
 799
 800 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
 801     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
 802         self.as_ref().map(|t| t.fold_with(folder))
 803     }
 804 }
 805
 806 macro_rules! CloneImpls {
 807     (<$lt_tcx:tt> $($ty:ty),+) => {
 808         $(
 809             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
 810                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
 811                     Clone::clone(self)
 812                 }
 813             }
 814         )+
 815     }
 816 }
 817
 818 CloneImpls!{ <'tcx>
 819     Span, Field, Mutability, ast::Name, ast::NodeId, usize, ConstVal<'tcx>, Region<'tcx>,
 820     Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
 821     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>
 822 }
 823
 824 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
 825     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 826         FieldPattern {
 827             field: self.field.fold_with(folder),
 828             pattern: self.pattern.fold_with(folder)
 829         }
 830     }
 831 }
 832
 833 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
 834     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 835         folder.fold_pattern(self)
 836     }
 837
 838     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 839         Pattern {
 840             ty: self.ty.fold_with(folder),
 841             span: self.span.fold_with(folder),
 842             kind: self.kind.fold_with(folder)
 843         }
 844     }
 845 }
 846
 847 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
 848     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 849         folder.fold_pattern_kind(self)
 850     }
 851
 852     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
 853         match *self {
 854             PatternKind::Wild => PatternKind::Wild,
 855             PatternKind::Binding {
 856                 mutability,
 857                 name,
 858                 mode,
 859                 var,
 860                 ty,
 861                 ref subpattern,
 862             } => PatternKind::Binding {
 863                 mutability: mutability.fold_with(folder),
 864                 name: name.fold_with(folder),
 865                 mode: mode.fold_with(folder),
 866                 var: var.fold_with(folder),
 867                 ty: ty.fold_with(folder),
 868                 subpattern: subpattern.fold_with(folder),
 869             },
 870             PatternKind::Variant {
 871                 adt_def,
 872                 substs,
 873                 variant_index,
 874                 ref subpatterns,
 875             } => PatternKind::Variant {
 876                 adt_def: adt_def.fold_with(folder),
 877                 substs: substs.fold_with(folder),
 878                 variant_index: variant_index.fold_with(folder),
 879                 subpatterns: subpatterns.fold_with(folder)
 880             },
 881             PatternKind::Leaf {
 882                 ref subpatterns,
 883             } => PatternKind::Leaf {
 884                 subpatterns: subpatterns.fold_with(folder),
 885             },
 886             PatternKind::Deref {
 887                 ref subpattern,
 888             } => PatternKind::Deref {
 889                 subpattern: subpattern.fold_with(folder),
 890             },
 891             PatternKind::Constant {
 892                 ref value
 893             } => PatternKind::Constant {
 894                 value: value.fold_with(folder)
 895             },
 896             PatternKind::Range {
 897                 ref lo,
 898                 ref hi,
 899                 ref end,
 900             } => PatternKind::Range {
 901                 lo: lo.fold_with(folder),
 902                 hi: hi.fold_with(folder),
 903                 end: end.clone(),
 904             },
 905             PatternKind::Slice {
 906                 ref prefix,
 907                 ref slice,
 908                 ref suffix,
 909             } => PatternKind::Slice {
 910                 prefix: prefix.fold_with(folder),
 911                 slice: slice.fold_with(folder),
 912                 suffix: suffix.fold_with(folder)
 913             },
 914             PatternKind::Array {
 915                 ref prefix,
 916                 ref slice,
 917                 ref suffix
 918             } => PatternKind::Array {
 919                 prefix: prefix.fold_with(folder),
 920                 slice: slice.fold_with(folder),
 921                 suffix: suffix.fold_with(folder)
 922             },
 923         }
 924     }
 925 }