src/librustc_middle/ty/fast_reject.rs

   1 use crate::ich::StableHashingContext;
   2 use crate::ty::{self, Ty, TyCtxt};
   3 use rustc_ast as ast;
   4 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
   5 use rustc_hir::def_id::DefId;
   6 use std::fmt::Debug;
   7 use std::hash::Hash;
   8 use std::mem;
   9
  10 use self::SimplifiedTypeGen::*;
  11
  12 pub type SimplifiedType = SimplifiedTypeGen<DefId>;
  13
  14 /// See `simplify_type`
  15 ///
  16 /// Note that we keep this type generic over the type of identifier it uses
  17 /// because we sometimes need to use SimplifiedTypeGen values as stable sorting
  18 /// keys (in which case we use a DefPathHash as id-type) but in the general case
  19 /// the non-stable but fast to construct DefId-version is the better choice.
  20 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, TyEncodable, TyDecodable)]
  21 pub enum SimplifiedTypeGen<D>
  22 where
  23     D: Copy + Debug + Ord + Eq,
  24 {
  25     BoolSimplifiedType,
  26     CharSimplifiedType,
  27     IntSimplifiedType(ast::IntTy),
  28     UintSimplifiedType(ast::UintTy),
  29     FloatSimplifiedType(ast::FloatTy),
  30     AdtSimplifiedType(D),
  31     StrSimplifiedType,
  32     ArraySimplifiedType,
  33     PtrSimplifiedType,
  34     NeverSimplifiedType,
  35     TupleSimplifiedType(usize),
  36     /// A trait object, all of whose components are markers
  37     /// (e.g., `dyn Send + Sync`).
  38     MarkerTraitObjectSimplifiedType,
  39     TraitSimplifiedType(D),
  40     ClosureSimplifiedType(D),
  41     GeneratorSimplifiedType(D),
  42     GeneratorWitnessSimplifiedType(usize),
  43     OpaqueSimplifiedType(D),
  44     FunctionSimplifiedType(usize),
  45     ParameterSimplifiedType,
  46     ForeignSimplifiedType(DefId),
  47 }
  48
  49 /// Tries to simplify a type by dropping type parameters, deref'ing away any reference types, etc.
  50 /// The idea is to get something simple that we can use to quickly decide if two types could unify
  51 /// during method lookup.
  52 ///
  53 /// If `can_simplify_params` is false, then we will fail to simplify type parameters entirely. This
  54 /// is useful when those type parameters would be instantiated with fresh type variables, since
  55 /// then we can't say much about whether two types would unify. Put another way,
  56 /// `can_simplify_params` should be true if type parameters appear free in `ty` and `false` if they
  57 /// are to be considered bound.
  58 pub fn simplify_type(
  59     tcx: TyCtxt<'_>,
  60     ty: Ty<'_>,
  61     can_simplify_params: bool,
  62 ) -> Option<SimplifiedType> {
  63     match ty.kind {
  64         ty::Bool => Some(BoolSimplifiedType),
  65         ty::Char => Some(CharSimplifiedType),
  66         ty::Int(int_type) => Some(IntSimplifiedType(int_type)),
  67         ty::Uint(uint_type) => Some(UintSimplifiedType(uint_type)),
  68         ty::Float(float_type) => Some(FloatSimplifiedType(float_type)),
  69         ty::Adt(def, _) => Some(AdtSimplifiedType(def.did)),
  70         ty::Str => Some(StrSimplifiedType),
  71         ty::Array(..) | ty::Slice(_) => Some(ArraySimplifiedType),
  72         ty::RawPtr(_) => Some(PtrSimplifiedType),
  73         ty::Dynamic(ref trait_info, ..) => match trait_info.principal_def_id() {
  74             Some(principal_def_id) if !tcx.trait_is_auto(principal_def_id) => {
  75                 Some(TraitSimplifiedType(principal_def_id))
  76             }
  77             _ => Some(MarkerTraitObjectSimplifiedType),
  78         },
  79         ty::Ref(_, ty, _) => {
  80             // since we introduce auto-refs during method lookup, we
  81             // just treat &T and T as equivalent from the point of
  82             // view of possibly unifying
  83             simplify_type(tcx, ty, can_simplify_params)
  84         }
  85         ty::FnDef(def_id, _) | ty::Closure(def_id, _) => Some(ClosureSimplifiedType(def_id)),
  86         ty::Generator(def_id, _, _) => Some(GeneratorSimplifiedType(def_id)),
  87         ty::GeneratorWitness(ref tys) => {
  88             Some(GeneratorWitnessSimplifiedType(tys.skip_binder().len()))
  89         }
  90         ty::Never => Some(NeverSimplifiedType),
  91         ty::Tuple(ref tys) => Some(TupleSimplifiedType(tys.len())),
  92         ty::FnPtr(ref f) => Some(FunctionSimplifiedType(f.skip_binder().inputs().len())),
  93         ty::Projection(_) | ty::Param(_) => {
  94             if can_simplify_params {
  95                 // In normalized types, projections don't unify with
  96                 // anything. when lazy normalization happens, this
  97                 // will change. It would still be nice to have a way
  98                 // to deal with known-not-to-unify-with-anything
  99                 // projections (e.g., the likes of <__S as Encoder>::Error).
 100                 Some(ParameterSimplifiedType)
 101             } else {
 102                 None
 103             }
 104         }
 105         ty::Opaque(def_id, _) => Some(OpaqueSimplifiedType(def_id)),
 106         ty::Foreign(def_id) => Some(ForeignSimplifiedType(def_id)),
 107         ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) | ty::Error(_) => None,
 108     }
 109 }
 110
 111 impl<D: Copy + Debug + Ord + Eq> SimplifiedTypeGen<D> {
 112     pub fn map_def<U, F>(self, map: F) -> SimplifiedTypeGen<U>
 113     where
 114         F: Fn(D) -> U,
 115         U: Copy + Debug + Ord + Eq,
 116     {
 117         match self {
 118             BoolSimplifiedType => BoolSimplifiedType,
 119             CharSimplifiedType => CharSimplifiedType,
 120             IntSimplifiedType(t) => IntSimplifiedType(t),
 121             UintSimplifiedType(t) => UintSimplifiedType(t),
 122             FloatSimplifiedType(t) => FloatSimplifiedType(t),
 123             AdtSimplifiedType(d) => AdtSimplifiedType(map(d)),
 124             StrSimplifiedType => StrSimplifiedType,
 125             ArraySimplifiedType => ArraySimplifiedType,
 126             PtrSimplifiedType => PtrSimplifiedType,
 127             NeverSimplifiedType => NeverSimplifiedType,
 128             MarkerTraitObjectSimplifiedType => MarkerTraitObjectSimplifiedType,
 129             TupleSimplifiedType(n) => TupleSimplifiedType(n),
 130             TraitSimplifiedType(d) => TraitSimplifiedType(map(d)),
 131             ClosureSimplifiedType(d) => ClosureSimplifiedType(map(d)),
 132             GeneratorSimplifiedType(d) => GeneratorSimplifiedType(map(d)),
 133             GeneratorWitnessSimplifiedType(n) => GeneratorWitnessSimplifiedType(n),
 134             OpaqueSimplifiedType(d) => OpaqueSimplifiedType(map(d)),
 135             FunctionSimplifiedType(n) => FunctionSimplifiedType(n),
 136             ParameterSimplifiedType => ParameterSimplifiedType,
 137             ForeignSimplifiedType(d) => ForeignSimplifiedType(d),
 138         }
 139     }
 140 }
 141
 142 impl<'a, D> HashStable<StableHashingContext<'a>> for SimplifiedTypeGen<D>
 143 where
 144     D: Copy + Debug + Ord + Eq + HashStable<StableHashingContext<'a>>,
 145 {
 146     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
 147         mem::discriminant(self).hash_stable(hcx, hasher);
 148         match *self {
 149             BoolSimplifiedType
 150             | CharSimplifiedType
 151             | StrSimplifiedType
 152             | ArraySimplifiedType
 153             | PtrSimplifiedType
 154             | NeverSimplifiedType
 155             | ParameterSimplifiedType
 156             | MarkerTraitObjectSimplifiedType => {
 157                 // nothing to do
 158             }
 159             IntSimplifiedType(t) => t.hash_stable(hcx, hasher),
 160             UintSimplifiedType(t) => t.hash_stable(hcx, hasher),
 161             FloatSimplifiedType(t) => t.hash_stable(hcx, hasher),
 162             AdtSimplifiedType(d) => d.hash_stable(hcx, hasher),
 163             TupleSimplifiedType(n) => n.hash_stable(hcx, hasher),
 164             TraitSimplifiedType(d) => d.hash_stable(hcx, hasher),
 165             ClosureSimplifiedType(d) => d.hash_stable(hcx, hasher),
 166             GeneratorSimplifiedType(d) => d.hash_stable(hcx, hasher),
 167             GeneratorWitnessSimplifiedType(n) => n.hash_stable(hcx, hasher),
 168             OpaqueSimplifiedType(d) => d.hash_stable(hcx, hasher),
 169             FunctionSimplifiedType(n) => n.hash_stable(hcx, hasher),
 170             ForeignSimplifiedType(d) => d.hash_stable(hcx, hasher),
 171         }
 172     }
 173 }