src/librustc/ty/fast_reject.rs

   1 // Copyright 2014 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 hir::def_id::DefId;
  12 use ich::StableHashingContext;
  13 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
  14                                            HashStable};
  15 use std::fmt::Debug;
  16 use std::hash::Hash;
  17 use std::mem;
  18 use syntax::ast;
  19 use ty::{self, Ty, TyCtxt};
  20
  21 use self::SimplifiedTypeGen::*;
  22
  23 pub type SimplifiedType = SimplifiedTypeGen<DefId>;
  24
  25 /// See `simplify_type`
  26 ///
  27 /// Note that we keep this type generic over the type of identifier it uses
  28 /// because we sometimes need to use SimplifiedTypeGen values as stable sorting
  29 /// keys (in which case we use a DefPathHash as id-type) but in the general case
  30 /// the non-stable but fast to construct DefId-version is the better choice.
  31 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
  32 pub enum SimplifiedTypeGen<D>
  33     where D: Copy + Debug + Ord + Eq + Hash
  34 {
  35     BoolSimplifiedType,
  36     CharSimplifiedType,
  37     IntSimplifiedType(ast::IntTy),
  38     UintSimplifiedType(ast::UintTy),
  39     FloatSimplifiedType(ast::FloatTy),
  40     AdtSimplifiedType(D),
  41     StrSimplifiedType,
  42     ArraySimplifiedType,
  43     PtrSimplifiedType,
  44     NeverSimplifiedType,
  45     TupleSimplifiedType(usize),
  46     TraitSimplifiedType(D),
  47     ClosureSimplifiedType(D),
  48     GeneratorSimplifiedType(D),
  49     AnonSimplifiedType(D),
  50     FunctionSimplifiedType(usize),
  51     ParameterSimplifiedType,
  52     ForeignSimplifiedType(DefId),
  53 }
  54
  55 /// Tries to simplify a type by dropping type parameters, deref'ing away any reference types, etc.
  56 /// The idea is to get something simple that we can use to quickly decide if two types could unify
  57 /// during method lookup.
  58 ///
  59 /// If `can_simplify_params` is false, then we will fail to simplify type parameters entirely. This
  60 /// is useful when those type parameters would be instantiated with fresh type variables, since
  61 /// then we can't say much about whether two types would unify. Put another way,
  62 /// `can_simplify_params` should be true if type parameters appear free in `ty` and `false` if they
  63 /// are to be considered bound.
  64 pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
  65                                      ty: Ty,
  66                                      can_simplify_params: bool)
  67                                      -> Option<SimplifiedType>
  68 {
  69     match ty.sty {
  70         ty::TyBool => Some(BoolSimplifiedType),
  71         ty::TyChar => Some(CharSimplifiedType),
  72         ty::TyInt(int_type) => Some(IntSimplifiedType(int_type)),
  73         ty::TyUint(uint_type) => Some(UintSimplifiedType(uint_type)),
  74         ty::TyFloat(float_type) => Some(FloatSimplifiedType(float_type)),
  75         ty::TyAdt(def, _) => Some(AdtSimplifiedType(def.did)),
  76         ty::TyStr => Some(StrSimplifiedType),
  77         ty::TyArray(..) | ty::TySlice(_) => Some(ArraySimplifiedType),
  78         ty::TyRawPtr(_) => Some(PtrSimplifiedType),
  79         ty::TyDynamic(ref trait_info, ..) => {
  80             trait_info.principal().map(|p| TraitSimplifiedType(p.def_id()))
  81         }
  82         ty::TyRef(_, mt) => {
  83             // since we introduce auto-refs during method lookup, we
  84             // just treat &T and T as equivalent from the point of
  85             // view of possibly unifying
  86             simplify_type(tcx, mt.ty, can_simplify_params)
  87         }
  88         ty::TyFnDef(def_id, _) |
  89         ty::TyClosure(def_id, _) => {
  90             Some(ClosureSimplifiedType(def_id))
  91         }
  92         ty::TyGenerator(def_id, _, _) => {
  93             Some(GeneratorSimplifiedType(def_id))
  94         }
  95         ty::TyNever => Some(NeverSimplifiedType),
  96         ty::TyTuple(ref tys, _) => {
  97             Some(TupleSimplifiedType(tys.len()))
  98         }
  99         ty::TyFnPtr(ref f) => {
 100             Some(FunctionSimplifiedType(f.skip_binder().inputs().len()))
 101         }
 102         ty::TyProjection(_) | ty::TyParam(_) => {
 103             if can_simplify_params {
 104                 // In normalized types, projections don't unify with
 105                 // anything. when lazy normalization happens, this
 106                 // will change. It would still be nice to have a way
 107                 // to deal with known-not-to-unify-with-anything
 108                 // projections (e.g. the likes of <__S as Encoder>::Error).
 109                 Some(ParameterSimplifiedType)
 110             } else {
 111                 None
 112             }
 113         }
 114         ty::TyAnon(def_id, _) => {
 115             Some(AnonSimplifiedType(def_id))
 116         }
 117         ty::TyForeign(def_id) => {
 118             Some(ForeignSimplifiedType(def_id))
 119         }
 120         ty::TyInfer(_) | ty::TyError => None,
 121     }
 122 }
 123
 124 impl<D: Copy + Debug + Ord + Eq + Hash> SimplifiedTypeGen<D> {
 125     pub fn map_def<U, F>(self, map: F) -> SimplifiedTypeGen<U>
 126         where F: Fn(D) -> U,
 127               U: Copy + Debug + Ord + Eq + Hash,
 128     {
 129         match self {
 130             BoolSimplifiedType => BoolSimplifiedType,
 131             CharSimplifiedType => CharSimplifiedType,
 132             IntSimplifiedType(t) => IntSimplifiedType(t),
 133             UintSimplifiedType(t) => UintSimplifiedType(t),
 134             FloatSimplifiedType(t) => FloatSimplifiedType(t),
 135             AdtSimplifiedType(d) => AdtSimplifiedType(map(d)),
 136             StrSimplifiedType => StrSimplifiedType,
 137             ArraySimplifiedType => ArraySimplifiedType,
 138             PtrSimplifiedType => PtrSimplifiedType,
 139             NeverSimplifiedType => NeverSimplifiedType,
 140             TupleSimplifiedType(n) => TupleSimplifiedType(n),
 141             TraitSimplifiedType(d) => TraitSimplifiedType(map(d)),
 142             ClosureSimplifiedType(d) => ClosureSimplifiedType(map(d)),
 143             GeneratorSimplifiedType(d) => GeneratorSimplifiedType(map(d)),
 144             AnonSimplifiedType(d) => AnonSimplifiedType(map(d)),
 145             FunctionSimplifiedType(n) => FunctionSimplifiedType(n),
 146             ParameterSimplifiedType => ParameterSimplifiedType,
 147             ForeignSimplifiedType(d) => ForeignSimplifiedType(d),
 148         }
 149     }
 150 }
 151
 152 impl<'gcx, D> HashStable<StableHashingContext<'gcx>> for SimplifiedTypeGen<D>
 153     where D: Copy + Debug + Ord + Eq + Hash +
 154              HashStable<StableHashingContext<'gcx>>,
 155 {
 156     fn hash_stable<W: StableHasherResult>(&self,
 157                                           hcx: &mut StableHashingContext<'gcx>,
 158                                           hasher: &mut StableHasher<W>) {
 159         mem::discriminant(self).hash_stable(hcx, hasher);
 160         match *self {
 161             BoolSimplifiedType |
 162             CharSimplifiedType |
 163             StrSimplifiedType |
 164             ArraySimplifiedType |
 165             PtrSimplifiedType |
 166             NeverSimplifiedType |
 167             ParameterSimplifiedType => {
 168                 // nothing to do
 169             }
 170             IntSimplifiedType(t) => t.hash_stable(hcx, hasher),
 171             UintSimplifiedType(t) => t.hash_stable(hcx, hasher),
 172             FloatSimplifiedType(t) => t.hash_stable(hcx, hasher),
 173             AdtSimplifiedType(d) => d.hash_stable(hcx, hasher),
 174             TupleSimplifiedType(n) => n.hash_stable(hcx, hasher),
 175             TraitSimplifiedType(d) => d.hash_stable(hcx, hasher),
 176             ClosureSimplifiedType(d) => d.hash_stable(hcx, hasher),
 177             GeneratorSimplifiedType(d) => d.hash_stable(hcx, hasher),
 178             AnonSimplifiedType(d) => d.hash_stable(hcx, hasher),
 179             FunctionSimplifiedType(n) => n.hash_stable(hcx, hasher),
 180             ForeignSimplifiedType(d) => d.hash_stable(hcx, hasher),
 181         }
 182     }
 183 }