src/librustc/middle/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 middle::def_id::DefId;
  12 use middle::ty::{self, Ty};
  13 use syntax::ast;
  14
  15 use self::SimplifiedType::*;
  16
  17 /// See `simplify_type
  18 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
  19 pub enum SimplifiedType {
  20     BoolSimplifiedType,
  21     CharSimplifiedType,
  22     IntSimplifiedType(ast::IntTy),
  23     UintSimplifiedType(ast::UintTy),
  24     FloatSimplifiedType(ast::FloatTy),
  25     EnumSimplifiedType(DefId),
  26     StrSimplifiedType,
  27     VecSimplifiedType,
  28     PtrSimplifiedType,
  29     TupleSimplifiedType(usize),
  30     TraitSimplifiedType(DefId),
  31     StructSimplifiedType(DefId),
  32     ClosureSimplifiedType(DefId),
  33     FunctionSimplifiedType(usize),
  34     ParameterSimplifiedType,
  35 }
  36
  37 /// Tries to simplify a type by dropping type parameters, deref'ing away any reference types, etc.
  38 /// The idea is to get something simple that we can use to quickly decide if two types could unify
  39 /// during method lookup.
  40 ///
  41 /// If `can_simplify_params` is false, then we will fail to simplify type parameters entirely. This
  42 /// is useful when those type parameters would be instantiated with fresh type variables, since
  43 /// then we can't say much about whether two types would unify. Put another way,
  44 /// `can_simplify_params` should be true if type parameters appear free in `ty` and `false` if they
  45 /// are to be considered bound.
  46 pub fn simplify_type(tcx: &ty::ctxt,
  47                      ty: Ty,
  48                      can_simplify_params: bool)
  49                      -> Option<SimplifiedType>
  50 {
  51     match ty.sty {
  52         ty::TyBool => Some(BoolSimplifiedType),
  53         ty::TyChar => Some(CharSimplifiedType),
  54         ty::TyInt(int_type) => Some(IntSimplifiedType(int_type)),
  55         ty::TyUint(uint_type) => Some(UintSimplifiedType(uint_type)),
  56         ty::TyFloat(float_type) => Some(FloatSimplifiedType(float_type)),
  57         ty::TyEnum(def, _) => Some(EnumSimplifiedType(def.did)),
  58         ty::TyStr => Some(StrSimplifiedType),
  59         ty::TyArray(..) | ty::TySlice(_) => Some(VecSimplifiedType),
  60         ty::TyRawPtr(_) => Some(PtrSimplifiedType),
  61         ty::TyTrait(ref trait_info) => {
  62             Some(TraitSimplifiedType(trait_info.principal_def_id()))
  63         }
  64         ty::TyStruct(def, _) => {
  65             Some(StructSimplifiedType(def.did))
  66         }
  67         ty::TyRef(_, mt) => {
  68             // since we introduce auto-refs during method lookup, we
  69             // just treat &T and T as equivalent from the point of
  70             // view of possibly unifying
  71             simplify_type(tcx, mt.ty, can_simplify_params)
  72         }
  73         ty::TyBox(_) => {
  74             // treat like we would treat `Box`
  75             match tcx.lang_items.require_owned_box() {
  76                 Ok(def_id) => Some(StructSimplifiedType(def_id)),
  77                 Err(msg) => tcx.sess.fatal(&msg),
  78             }
  79         }
  80         ty::TyClosure(def_id, _) => {
  81             Some(ClosureSimplifiedType(def_id))
  82         }
  83         ty::TyTuple(ref tys) => {
  84             Some(TupleSimplifiedType(tys.len()))
  85         }
  86         ty::TyBareFn(_, ref f) => {
  87             Some(FunctionSimplifiedType(f.sig.0.inputs.len()))
  88         }
  89         ty::TyProjection(_) | ty::TyParam(_) => {
  90             if can_simplify_params {
  91                 // In normalized types, projections don't unify with
  92                 // anything. when lazy normalization happens, this
  93                 // will change. It would still be nice to have a way
  94                 // to deal with known-not-to-unify-with-anything
  95                 // projections (e.g. the likes of <__S as Encoder>::Error).
  96                 Some(ParameterSimplifiedType)
  97             } else {
  98                 None
  99             }
 100         }
 101         ty::TyInfer(_) | ty::TyError => None,
 102     }
 103 }