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 ty::{self, Ty, TyCtxt};
  13 use syntax::ast;
  14
  15 use self::SimplifiedType::*;
  16
  17 /// See `simplify_type
  18 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
  19 pub enum SimplifiedType {
  20     BoolSimplifiedType,
  21     CharSimplifiedType,
  22     IntSimplifiedType(ast::IntTy),
  23     UintSimplifiedType(ast::UintTy),
  24     FloatSimplifiedType(ast::FloatTy),
  25     AdtSimplifiedType(DefId),
  26     StrSimplifiedType,
  27     ArraySimplifiedType,
  28     PtrSimplifiedType,
  29     NeverSimplifiedType,
  30     TupleSimplifiedType(usize),
  31     TraitSimplifiedType(DefId),
  32     ClosureSimplifiedType(DefId),
  33     AnonSimplifiedType(DefId),
  34     FunctionSimplifiedType(usize),
  35     ParameterSimplifiedType,
  36 }
  37
  38 /// Tries to simplify a type by dropping type parameters, deref'ing away any reference types, etc.
  39 /// The idea is to get something simple that we can use to quickly decide if two types could unify
  40 /// during method lookup.
  41 ///
  42 /// If `can_simplify_params` is false, then we will fail to simplify type parameters entirely. This
  43 /// is useful when those type parameters would be instantiated with fresh type variables, since
  44 /// then we can't say much about whether two types would unify. Put another way,
  45 /// `can_simplify_params` should be true if type parameters appear free in `ty` and `false` if they
  46 /// are to be considered bound.
  47 pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
  48                                      ty: Ty,
  49                                      can_simplify_params: bool)
  50                                      -> Option<SimplifiedType>
  51 {
  52     match ty.sty {
  53         ty::TyBool => Some(BoolSimplifiedType),
  54         ty::TyChar => Some(CharSimplifiedType),
  55         ty::TyInt(int_type) => Some(IntSimplifiedType(int_type)),
  56         ty::TyUint(uint_type) => Some(UintSimplifiedType(uint_type)),
  57         ty::TyFloat(float_type) => Some(FloatSimplifiedType(float_type)),
  58         ty::TyAdt(def, _) => Some(AdtSimplifiedType(def.did)),
  59         ty::TyStr => Some(StrSimplifiedType),
  60         ty::TyArray(..) | ty::TySlice(_) => Some(ArraySimplifiedType),
  61         ty::TyRawPtr(_) => Some(PtrSimplifiedType),
  62         ty::TyDynamic(ref trait_info, ..) => {
  63             trait_info.principal().map(|p| TraitSimplifiedType(p.def_id()))
  64         }
  65         ty::TyRef(_, mt) => {
  66             // since we introduce auto-refs during method lookup, we
  67             // just treat &T and T as equivalent from the point of
  68             // view of possibly unifying
  69             simplify_type(tcx, mt.ty, can_simplify_params)
  70         }
  71         ty::TyClosure(def_id, _) => {
  72             Some(ClosureSimplifiedType(def_id))
  73         }
  74         ty::TyNever => Some(NeverSimplifiedType),
  75         ty::TyTuple(ref tys, _) => {
  76             Some(TupleSimplifiedType(tys.len()))
  77         }
  78         ty::TyFnDef(.., ref f) | ty::TyFnPtr(ref f) => {
  79             Some(FunctionSimplifiedType(f.skip_binder().inputs().len()))
  80         }
  81         ty::TyProjection(_) | ty::TyParam(_) => {
  82             if can_simplify_params {
  83                 // In normalized types, projections don't unify with
  84                 // anything. when lazy normalization happens, this
  85                 // will change. It would still be nice to have a way
  86                 // to deal with known-not-to-unify-with-anything
  87                 // projections (e.g. the likes of <__S as Encoder>::Error).
  88                 Some(ParameterSimplifiedType)
  89             } else {
  90                 None
  91             }
  92         }
  93         ty::TyAnon(def_id, _) => {
  94             Some(AnonSimplifiedType(def_id))
  95         }
  96         ty::TyInfer(_) | ty::TyError => None,
  97     }
  98 }