src/librustc_typeck/coherence/orphan.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 //! Orphan checker: every impl either implements a trait defined in this
  12 //! crate or pertains to a type defined in this crate.
  13
  14 use middle::traits;
  15 use middle::ty;
  16 use syntax::ast::{Item, ItemImpl};
  17 use syntax::ast;
  18 use syntax::ast_util;
  19 use syntax::codemap::Span;
  20 use syntax::visit;
  21
  22 pub fn check(tcx: &ty::ctxt) {
  23     let mut orphan = OrphanChecker { tcx: tcx };
  24     visit::walk_crate(&mut orphan, tcx.map.krate());
  25 }
  26
  27 struct OrphanChecker<'cx, 'tcx:'cx> {
  28     tcx: &'cx ty::ctxt<'tcx>
  29 }
  30
  31 impl<'cx, 'tcx> OrphanChecker<'cx, 'tcx> {
  32     fn check_def_id(&self, item: &ast::Item, def_id: ast::DefId) {
  33         if def_id.krate != ast::LOCAL_CRATE {
  34             span_err!(self.tcx.sess, item.span, E0116,
  35                       "cannot define inherent `impl` for a type outside of the \
  36                        crate where the type is defined; define and implement \
  37                        a trait or new type instead");
  38         }
  39     }
  40
  41     fn check_primitive_impl(&self,
  42                             impl_def_id: ast::DefId,
  43                             lang_def_id: Option<ast::DefId>,
  44                             lang: &str,
  45                             ty: &str,
  46                             span: Span) {
  47         match lang_def_id {
  48             Some(lang_def_id) if lang_def_id == impl_def_id => { /* OK */ },
  49             _ => {
  50                 span_err!(self.tcx.sess, span, E0390,
  51                           "only a single inherent implementation marked with `#[lang = \"{}\"]` \
  52                            is allowed for the `{}` primitive", lang, ty);
  53             }
  54         }
  55     }
  56
  57     /// Checks exactly one impl for orphan rules and other such
  58     /// restrictions.  In this fn, it can happen that multiple errors
  59     /// apply to a specific impl, so just return after reporting one
  60     /// to prevent inundating the user with a bunch of similar error
  61     /// reports.
  62     fn check_item(&self, item: &ast::Item) {
  63         let def_id = ast_util::local_def(item.id);
  64         match item.node {
  65             ast::ItemImpl(_, _, _, None, _, _) => {
  66                 // For inherent impls, self type must be a nominal type
  67                 // defined in this crate.
  68                 debug!("coherence2::orphan check: inherent impl {}",
  69                        self.tcx.map.node_to_string(item.id));
  70                 let self_ty = ty::lookup_item_type(self.tcx, def_id).ty;
  71                 match self_ty.sty {
  72                     ty::TyEnum(def_id, _) |
  73                     ty::TyStruct(def_id, _) => {
  74                         self.check_def_id(item, def_id);
  75                     }
  76                     ty::TyTrait(ref data) => {
  77                         self.check_def_id(item, data.principal_def_id());
  78                     }
  79                     ty::TyBox(..) => {
  80                         self.check_def_id(item, self.tcx.lang_items.owned_box().unwrap());
  81                     }
  82                     ty::TyChar => {
  83                         self.check_primitive_impl(def_id,
  84                                                   self.tcx.lang_items.char_impl(),
  85                                                   "char",
  86                                                   "char",
  87                                                   item.span);
  88                     }
  89                     ty::TyStr => {
  90                         self.check_primitive_impl(def_id,
  91                                                   self.tcx.lang_items.str_impl(),
  92                                                   "str",
  93                                                   "str",
  94                                                   item.span);
  95                     }
  96                     ty::TySlice(_) => {
  97                         self.check_primitive_impl(def_id,
  98                                                   self.tcx.lang_items.slice_impl(),
  99                                                   "slice",
 100                                                   "[T]",
 101                                                   item.span);
 102                     }
 103                     ty::TyRawPtr(ty::mt { ty: _, mutbl: ast::MutImmutable }) => {
 104                         self.check_primitive_impl(def_id,
 105                                                   self.tcx.lang_items.const_ptr_impl(),
 106                                                   "const_ptr",
 107                                                   "*const T",
 108                                                   item.span);
 109                     }
 110                     ty::TyRawPtr(ty::mt { ty: _, mutbl: ast::MutMutable }) => {
 111                         self.check_primitive_impl(def_id,
 112                                                   self.tcx.lang_items.mut_ptr_impl(),
 113                                                   "mut_ptr",
 114                                                   "*mut T",
 115                                                   item.span);
 116                     }
 117                     ty::TyInt(ast::TyI8) => {
 118                         self.check_primitive_impl(def_id,
 119                                                   self.tcx.lang_items.i8_impl(),
 120                                                   "i8",
 121                                                   "i8",
 122                                                   item.span);
 123                     }
 124                     ty::TyInt(ast::TyI16) => {
 125                         self.check_primitive_impl(def_id,
 126                                                   self.tcx.lang_items.i16_impl(),
 127                                                   "i16",
 128                                                   "i16",
 129                                                   item.span);
 130                     }
 131                     ty::TyInt(ast::TyI32) => {
 132                         self.check_primitive_impl(def_id,
 133                                                   self.tcx.lang_items.i32_impl(),
 134                                                   "i32",
 135                                                   "i32",
 136                                                   item.span);
 137                     }
 138                     ty::TyInt(ast::TyI64) => {
 139                         self.check_primitive_impl(def_id,
 140                                                   self.tcx.lang_items.i64_impl(),
 141                                                   "i64",
 142                                                   "i64",
 143                                                   item.span);
 144                     }
 145                     ty::TyInt(ast::TyIs) => {
 146                         self.check_primitive_impl(def_id,
 147                                                   self.tcx.lang_items.isize_impl(),
 148                                                   "isize",
 149                                                   "isize",
 150                                                   item.span);
 151                     }
 152                     ty::TyUint(ast::TyU8) => {
 153                         self.check_primitive_impl(def_id,
 154                                                   self.tcx.lang_items.u8_impl(),
 155                                                   "u8",
 156                                                   "u8",
 157                                                   item.span);
 158                     }
 159                     ty::TyUint(ast::TyU16) => {
 160                         self.check_primitive_impl(def_id,
 161                                                   self.tcx.lang_items.u16_impl(),
 162                                                   "u16",
 163                                                   "u16",
 164                                                   item.span);
 165                     }
 166                     ty::TyUint(ast::TyU32) => {
 167                         self.check_primitive_impl(def_id,
 168                                                   self.tcx.lang_items.u32_impl(),
 169                                                   "u32",
 170                                                   "u32",
 171                                                   item.span);
 172                     }
 173                     ty::TyUint(ast::TyU64) => {
 174                         self.check_primitive_impl(def_id,
 175                                                   self.tcx.lang_items.u64_impl(),
 176                                                   "u64",
 177                                                   "u64",
 178                                                   item.span);
 179                     }
 180                     ty::TyUint(ast::TyUs) => {
 181                         self.check_primitive_impl(def_id,
 182                                                   self.tcx.lang_items.usize_impl(),
 183                                                   "usize",
 184                                                   "usize",
 185                                                   item.span);
 186                     }
 187                     ty::TyFloat(ast::TyF32) => {
 188                         self.check_primitive_impl(def_id,
 189                                                   self.tcx.lang_items.f32_impl(),
 190                                                   "f32",
 191                                                   "f32",
 192                                                   item.span);
 193                     }
 194                     ty::TyFloat(ast::TyF64) => {
 195                         self.check_primitive_impl(def_id,
 196                                                   self.tcx.lang_items.f64_impl(),
 197                                                   "f64",
 198                                                   "f64",
 199                                                   item.span);
 200                     }
 201                     _ => {
 202                         span_err!(self.tcx.sess, item.span, E0118,
 203                                   "no base type found for inherent implementation; \
 204                                    implement a trait or new type instead");
 205                         return;
 206                     }
 207                 }
 208             }
 209             ast::ItemImpl(_, _, _, Some(_), _, _) => {
 210                 // "Trait" impl
 211                 debug!("coherence2::orphan check: trait impl {}",
 212                        self.tcx.map.node_to_string(item.id));
 213                 let trait_ref = ty::impl_trait_ref(self.tcx, def_id).unwrap();
 214                 let trait_def_id = trait_ref.def_id;
 215                 match traits::orphan_check(self.tcx, def_id) {
 216                     Ok(()) => { }
 217                     Err(traits::OrphanCheckErr::NoLocalInputType) => {
 218                         span_err!(
 219                             self.tcx.sess, item.span, E0117,
 220                             "the impl does not reference any \
 221                              types defined in this crate; \
 222                              only traits defined in the current crate can be \
 223                              implemented for arbitrary types");
 224                         return;
 225                     }
 226                     Err(traits::OrphanCheckErr::UncoveredTy(param_ty)) => {
 227                         span_err!(self.tcx.sess, item.span, E0210,
 228                                 "type parameter `{}` must be used as the type parameter for \
 229                                  some local type (e.g. `MyStruct<T>`); only traits defined in \
 230                                  the current crate can be implemented for a type parameter",
 231                                 param_ty);
 232                         return;
 233                     }
 234                 }
 235
 236                 // In addition to the above rules, we restrict impls of defaulted traits
 237                 // so that they can only be implemented on structs/enums. To see why this
 238                 // restriction exists, consider the following example (#22978). Imagine
 239                 // that crate A defines a defaulted trait `Foo` and a fn that operates
 240                 // on pairs of types:
 241                 //
 242                 // ```
 243                 // // Crate A
 244                 // trait Foo { }
 245                 // impl Foo for .. { }
 246                 // fn two_foos<A:Foo,B:Foo>(..) {
 247                 //     one_foo::<(A,B)>(..)
 248                 // }
 249                 // fn one_foo<T:Foo>(..) { .. }
 250                 // ```
 251                 //
 252                 // This type-checks fine; in particular the fn
 253                 // `two_foos` is able to conclude that `(A,B):Foo`
 254                 // because `A:Foo` and `B:Foo`.
 255                 //
 256                 // Now imagine that crate B comes along and does the following:
 257                 //
 258                 // ```
 259                 // struct A { }
 260                 // struct B { }
 261                 // impl Foo for A { }
 262                 // impl Foo for B { }
 263                 // impl !Send for (A, B) { }
 264                 // ```
 265                 //
 266                 // This final impl is legal according to the orpan
 267                 // rules, but it invalidates the reasoning from
 268                 // `two_foos` above.
 269                 debug!("trait_ref={:?} trait_def_id={:?} trait_has_default_impl={}",
 270                        trait_ref,
 271                        trait_def_id,
 272                        ty::trait_has_default_impl(self.tcx, trait_def_id));
 273                 if
 274                     ty::trait_has_default_impl(self.tcx, trait_def_id) &&
 275                     trait_def_id.krate != ast::LOCAL_CRATE
 276                 {
 277                     let self_ty = trait_ref.self_ty();
 278                     let opt_self_def_id = match self_ty.sty {
 279                         ty::TyStruct(self_def_id, _) | ty::TyEnum(self_def_id, _) =>
 280                             Some(self_def_id),
 281                         ty::TyBox(..) =>
 282                             self.tcx.lang_items.owned_box(),
 283                         _ =>
 284                             None
 285                     };
 286
 287                     let msg = match opt_self_def_id {
 288                         // We only want to permit structs/enums, but not *all* structs/enums.
 289                         // They must be local to the current crate, so that people
 290                         // can't do `unsafe impl Send for Rc<SomethingLocal>` or
 291                         // `impl !Send for Box<SomethingLocalAndSend>`.
 292                         Some(self_def_id) => {
 293                             if self_def_id.krate == ast::LOCAL_CRATE {
 294                                 None
 295                             } else {
 296                                 Some(format!(
 297                                     "cross-crate traits with a default impl, like `{}`, \
 298                                      can only be implemented for a struct/enum type \
 299                                      defined in the current crate",
 300                                     ty::item_path_str(self.tcx, trait_def_id)))
 301                             }
 302                         }
 303                         _ => {
 304                             Some(format!(
 305                                 "cross-crate traits with a default impl, like `{}`, \
 306                                  can only be implemented for a struct/enum type, \
 307                                  not `{}`",
 308                                 ty::item_path_str(self.tcx, trait_def_id),
 309                                 self_ty))
 310                         }
 311                     };
 312
 313                     if let Some(msg) = msg {
 314                         span_err!(self.tcx.sess, item.span, E0321, "{}", msg);
 315                         return;
 316                     }
 317                 }
 318
 319                 // Disallow *all* explicit impls of `Sized` and `Unsize` for now.
 320                 if Some(trait_def_id) == self.tcx.lang_items.sized_trait() {
 321                     span_err!(self.tcx.sess, item.span, E0322,
 322                               "explicit impls for the `Sized` trait are not permitted");
 323                     return;
 324                 }
 325                 if Some(trait_def_id) == self.tcx.lang_items.unsize_trait() {
 326                     span_err!(self.tcx.sess, item.span, E0328,
 327                               "explicit impls for the `Unsize` trait are not permitted");
 328                     return;
 329                 }
 330             }
 331             ast::ItemDefaultImpl(..) => {
 332                 // "Trait" impl
 333                 debug!("coherence2::orphan check: default trait impl {}",
 334                        self.tcx.map.node_to_string(item.id));
 335                 let trait_ref = ty::impl_trait_ref(self.tcx, def_id).unwrap();
 336                 if trait_ref.def_id.krate != ast::LOCAL_CRATE {
 337                     span_err!(self.tcx.sess, item.span, E0318,
 338                               "cannot create default implementations for traits outside the \
 339                                crate they're defined in; define a new trait instead");
 340                     return;
 341                 }
 342             }
 343             _ => {
 344                 // Not an impl
 345             }
 346         }
 347     }
 348 }
 349
 350 impl<'cx, 'tcx,'v> visit::Visitor<'v> for OrphanChecker<'cx, 'tcx> {
 351     fn visit_item(&mut self, item: &ast::Item) {
 352         self.check_item(item);
 353         visit::walk_item(self, item);
 354     }
 355 }