src/librustc/middle/subst.rs

   1 // Copyright 2012 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 // Type substitutions.
  12
  13 use middle::ty;
  14 use middle::ty_fold;
  15 use middle::ty_fold::TypeFolder;
  16 use util::ppaux::Repr;
  17
  18 use std::rc::Rc;
  19 use syntax::codemap::Span;
  20 use syntax::owned_slice::OwnedSlice;
  21
  22 ///////////////////////////////////////////////////////////////////////////
  23 // Public trait `Subst`
  24 //
  25 // Just call `foo.subst(tcx, substs)` to perform a substitution across
  26 // `foo`.
  27 // Or use `foo.subst_spanned(tcx, substs, Some(span))` when there is more
  28 // information available (for better errors).
  29
  30 pub trait Subst {
  31     fn subst(&self, tcx: &ty::ctxt, substs: &ty::substs) -> Self {
  32         self.subst_spanned(tcx, substs, None)
  33     }
  34     fn subst_spanned(&self, tcx: &ty::ctxt,
  35                      substs: &ty::substs,
  36                      span: Option<Span>) -> Self;
  37 }
  38
  39 ///////////////////////////////////////////////////////////////////////////
  40 // Substitution over types
  41 //
  42 // Because this is so common, we make a special optimization to avoid
  43 // doing anything if `substs` is a no-op.  I tried to generalize these
  44 // to all subst methods but ran into trouble due to the limitations of
  45 // our current method/trait matching algorithm. - Niko
  46
  47 impl Subst for ty::t {
  48     fn subst_spanned(&self, tcx: &ty::ctxt,
  49                      substs: &ty::substs,
  50                      span: Option<Span>) -> ty::t {
  51         if ty::substs_is_noop(substs) && !ty::type_has_params(*self) {
  52             *self
  53         } else {
  54             let mut folder = SubstFolder {
  55                 tcx: tcx,
  56                 substs: substs,
  57                 span: span,
  58                 root_ty: Some(*self)
  59             };
  60             folder.fold_ty(*self)
  61         }
  62     }
  63 }
  64
  65 struct SubstFolder<'a> {
  66     tcx: &'a ty::ctxt,
  67     substs: &'a ty::substs,
  68
  69     // The location for which the substitution is performed, if available.
  70     span: Option<Span>,
  71
  72     // The root type that is being substituted, if available.
  73     root_ty: Option<ty::t>
  74 }
  75
  76 impl<'a> TypeFolder for SubstFolder<'a> {
  77     fn tcx<'a>(&'a self) -> &'a ty::ctxt { self.tcx }
  78
  79     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
  80         r.subst(self.tcx, self.substs)
  81     }
  82
  83     fn fold_ty(&mut self, t: ty::t) -> ty::t {
  84         if !ty::type_needs_subst(t) {
  85             return t;
  86         }
  87
  88         match ty::get(t).sty {
  89             ty::ty_param(p) => {
  90                 if p.idx < self.substs.tps.len() {
  91                     *self.substs.tps.get(p.idx)
  92                 } else {
  93                     let root_msg = match self.root_ty {
  94                         Some(root) => format!(" in the substitution of `{}`",
  95                                               root.repr(self.tcx)),
  96                         None => ~""
  97                     };
  98                     let m = format!("missing type param `{}`{}",
  99                                     t.repr(self.tcx), root_msg);
 100                     match self.span {
 101                         Some(span) => self.tcx.sess.span_err(span, m),
 102                         None => self.tcx.sess.err(m)
 103                     }
 104                     ty::mk_err()
 105                 }
 106             }
 107             ty::ty_self(_) => {
 108                 match self.substs.self_ty {
 109                     Some(ty) => ty,
 110                     None => {
 111                         let root_msg = match self.root_ty {
 112                             Some(root) => format!(" in the substitution of `{}`",
 113                                                   root.repr(self.tcx)),
 114                             None => ~""
 115                         };
 116                         let m = format!("missing `Self` type param{}", root_msg);
 117                         match self.span {
 118                             Some(span) => self.tcx.sess.span_err(span, m),
 119                             None => self.tcx.sess.err(m)
 120                         }
 121                         ty::mk_err()
 122                     }
 123                 }
 124             }
 125             _ => ty_fold::super_fold_ty(self, t)
 126         }
 127     }
 128 }
 129
 130 ///////////////////////////////////////////////////////////////////////////
 131 // Other types
 132
 133 impl<T:Subst> Subst for Vec<T> {
 134     fn subst_spanned(&self, tcx: &ty::ctxt,
 135                      substs: &ty::substs,
 136                      span: Option<Span>) -> Vec<T> {
 137         self.map(|t| t.subst_spanned(tcx, substs, span))
 138     }
 139 }
 140 impl<T:Subst> Subst for Rc<T> {
 141     fn subst_spanned(&self, tcx: &ty::ctxt,
 142                      substs: &ty::substs,
 143                      span: Option<Span>) -> Rc<T> {
 144         Rc::new((**self).subst_spanned(tcx, substs, span))
 145     }
 146 }
 147
 148 impl<T:Subst> Subst for OwnedSlice<T> {
 149     fn subst_spanned(&self, tcx: &ty::ctxt,
 150                      substs: &ty::substs,
 151                      span: Option<Span>) -> OwnedSlice<T> {
 152         self.map(|t| t.subst_spanned(tcx, substs, span))
 153     }
 154 }
 155
 156 impl<T:Subst + 'static> Subst for @T {
 157     fn subst_spanned(&self, tcx: &ty::ctxt,
 158                      substs: &ty::substs,
 159                      span: Option<Span>) -> @T {
 160         match self {
 161             t => @(**t).subst_spanned(tcx, substs, span)
 162         }
 163     }
 164 }
 165
 166 impl<T:Subst> Subst for Option<T> {
 167     fn subst_spanned(&self, tcx: &ty::ctxt,
 168                      substs: &ty::substs,
 169                      span: Option<Span>) -> Option<T> {
 170         self.as_ref().map(|t| t.subst_spanned(tcx, substs, span))
 171     }
 172 }
 173
 174 impl Subst for ty::TraitRef {
 175     fn subst_spanned(&self, tcx: &ty::ctxt,
 176                      substs: &ty::substs,
 177                      span: Option<Span>) -> ty::TraitRef {
 178         ty::TraitRef {
 179             def_id: self.def_id,
 180             substs: self.substs.subst_spanned(tcx, substs, span)
 181         }
 182     }
 183 }
 184
 185 impl Subst for ty::substs {
 186     fn subst_spanned(&self, tcx: &ty::ctxt,
 187                      substs: &ty::substs,
 188                      span: Option<Span>) -> ty::substs {
 189         ty::substs {
 190             regions: self.regions.subst_spanned(tcx, substs, span),
 191             self_ty: self.self_ty.map(|typ| typ.subst_spanned(tcx, substs, span)),
 192             tps: self.tps.map(|typ| typ.subst_spanned(tcx, substs, span))
 193         }
 194     }
 195 }
 196
 197 impl Subst for ty::RegionSubsts {
 198     fn subst_spanned(&self, tcx: &ty::ctxt,
 199                      substs: &ty::substs,
 200                      span: Option<Span>) -> ty::RegionSubsts {
 201         match *self {
 202             ty::ErasedRegions => {
 203                 ty::ErasedRegions
 204             }
 205             ty::NonerasedRegions(ref regions) => {
 206                 ty::NonerasedRegions(regions.subst_spanned(tcx, substs, span))
 207             }
 208         }
 209     }
 210 }
 211
 212 impl Subst for ty::BareFnTy {
 213     fn subst_spanned(&self, tcx: &ty::ctxt,
 214                      substs: &ty::substs,
 215                      span: Option<Span>) -> ty::BareFnTy {
 216         let mut folder = SubstFolder {
 217             tcx: tcx,
 218             substs: substs,
 219             span: span,
 220             root_ty: None
 221         };
 222         folder.fold_bare_fn_ty(self)
 223     }
 224 }
 225
 226 impl Subst for ty::ParamBounds {
 227     fn subst_spanned(&self, tcx: &ty::ctxt,
 228                      substs: &ty::substs,
 229                      span: Option<Span>) -> ty::ParamBounds {
 230         ty::ParamBounds {
 231             builtin_bounds: self.builtin_bounds,
 232             trait_bounds: self.trait_bounds.subst_spanned(tcx, substs, span)
 233         }
 234     }
 235 }
 236
 237 impl Subst for ty::TypeParameterDef {
 238     fn subst_spanned(&self, tcx: &ty::ctxt,
 239                      substs: &ty::substs,
 240                      span: Option<Span>) -> ty::TypeParameterDef {
 241         ty::TypeParameterDef {
 242             ident: self.ident,
 243             def_id: self.def_id,
 244             bounds: self.bounds.subst_spanned(tcx, substs, span),
 245             default: self.default.map(|x| x.subst_spanned(tcx, substs, span))
 246         }
 247     }
 248 }
 249
 250 impl Subst for ty::Generics {
 251     fn subst_spanned(&self, tcx: &ty::ctxt,
 252                      substs: &ty::substs,
 253                      span: Option<Span>) -> ty::Generics {
 254         ty::Generics {
 255             type_param_defs: self.type_param_defs.subst_spanned(tcx, substs, span),
 256             region_param_defs: self.region_param_defs.subst_spanned(tcx, substs, span),
 257         }
 258     }
 259 }
 260
 261 impl Subst for ty::RegionParameterDef {
 262     fn subst_spanned(&self, _: &ty::ctxt,
 263                      _: &ty::substs,
 264                      _: Option<Span>) -> ty::RegionParameterDef {
 265         *self
 266     }
 267 }
 268
 269 impl Subst for ty::Region {
 270     fn subst_spanned(&self, _tcx: &ty::ctxt,
 271                      substs: &ty::substs,
 272                      _: Option<Span>) -> ty::Region {
 273         // Note: This routine only handles regions that are bound on
 274         // type declarationss and other outer declarations, not those
 275         // bound in *fn types*. Region substitution of the bound
 276         // regions that appear in a function signature is done using
 277         // the specialized routine
 278         // `middle::typeck::check::regionmanip::replace_late_regions_in_fn_sig()`.
 279         match self {
 280             &ty::ReEarlyBound(_, i, _) => {
 281                 match substs.regions {
 282                     ty::ErasedRegions => ty::ReStatic,
 283                     ty::NonerasedRegions(ref regions) => *regions.get(i),
 284                 }
 285             }
 286             _ => *self
 287         }
 288     }
 289 }
 290
 291 impl Subst for ty::ty_param_bounds_and_ty {
 292     fn subst_spanned(&self, tcx: &ty::ctxt,
 293                      substs: &ty::substs,
 294                      span: Option<Span>) -> ty::ty_param_bounds_and_ty {
 295         ty::ty_param_bounds_and_ty {
 296             generics: self.generics.subst_spanned(tcx, substs, span),
 297             ty: self.ty.subst_spanned(tcx, substs, span)
 298         }
 299     }
 300 }