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::cstore::LOCAL_CRATE;
  15 use middle::def_id::DefId;
  16 use middle::traits;
  17 use middle::ty;
  18 use syntax::ast;
  19 use syntax::codemap::Span;
  20 use rustc_front::intravisit;
  21 use rustc_front::hir;
  22 use rustc_front::hir::{Item, ItemImpl};
  23
  24 pub fn check(tcx: &ty::ctxt) {
  25     let mut orphan = OrphanChecker { tcx: tcx };
  26     tcx.map.krate().visit_all_items(&mut orphan);
  27 }
  28
  29 struct OrphanChecker<'cx, 'tcx:'cx> {
  30     tcx: &'cx ty::ctxt<'tcx>
  31 }
  32
  33 impl<'cx, 'tcx> OrphanChecker<'cx, 'tcx> {
  34     fn check_def_id(&self, item: &hir::Item, def_id: DefId) {
  35         if def_id.krate != LOCAL_CRATE {
  36             span_err!(self.tcx.sess, item.span, E0116,
  37                       "cannot define inherent `impl` for a type outside of the \
  38                        crate where the type is defined; define and implement \
  39                        a trait or new type instead");
  40         }
  41     }
  42
  43     fn check_primitive_impl(&self,
  44                             impl_def_id: DefId,
  45                             lang_def_id: Option<DefId>,
  46                             lang: &str,
  47                             ty: &str,
  48                             span: Span) {
  49         match lang_def_id {
  50             Some(lang_def_id) if lang_def_id == impl_def_id => { /* OK */ },
  51             _ => {
  52                 span_err!(self.tcx.sess, span, E0390,
  53                           "only a single inherent implementation marked with `#[lang = \"{}\"]` \
  54                            is allowed for the `{}` primitive", lang, ty);
  55                 span_help!(self.tcx.sess, span,
  56                            "consider using a trait to implement these methods");
  57             }
  58         }
  59     }
  60
  61     /// Checks exactly one impl for orphan rules and other such
  62     /// restrictions.  In this fn, it can happen that multiple errors
  63     /// apply to a specific impl, so just return after reporting one
  64     /// to prevent inundating the user with a bunch of similar error
  65     /// reports.
  66     fn check_item(&self, item: &hir::Item) {
  67         let def_id = self.tcx.map.local_def_id(item.id);
  68         match item.node {
  69             hir::ItemImpl(_, _, _, None, _, _) => {
  70                 // For inherent impls, self type must be a nominal type
  71                 // defined in this crate.
  72                 debug!("coherence2::orphan check: inherent impl {}",
  73                        self.tcx.map.node_to_string(item.id));
  74                 let self_ty = self.tcx.lookup_item_type(def_id).ty;
  75                 match self_ty.sty {
  76                     ty::TyEnum(def, _) |
  77                     ty::TyStruct(def, _) => {
  78                         self.check_def_id(item, def.did);
  79                     }
  80                     ty::TyTrait(ref data) => {
  81                         self.check_def_id(item, data.principal_def_id());
  82                     }
  83                     ty::TyBox(..) => {
  84                         match self.tcx.lang_items.require_owned_box() {
  85                             Ok(trait_id) => self.check_def_id(item, trait_id),
  86                             Err(msg) => self.tcx.sess.span_fatal(item.span, &msg),
  87                         }
  88                     }
  89                     ty::TyChar => {
  90                         self.check_primitive_impl(def_id,
  91                                                   self.tcx.lang_items.char_impl(),
  92                                                   "char",
  93                                                   "char",
  94                                                   item.span);
  95                     }
  96                     ty::TyStr => {
  97                         self.check_primitive_impl(def_id,
  98                                                   self.tcx.lang_items.str_impl(),
  99                                                   "str",
 100                                                   "str",
 101                                                   item.span);
 102                     }
 103                     ty::TySlice(_) => {
 104                         self.check_primitive_impl(def_id,
 105                                                   self.tcx.lang_items.slice_impl(),
 106                                                   "slice",
 107                                                   "[T]",
 108                                                   item.span);
 109                     }
 110                     ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutImmutable }) => {
 111                         self.check_primitive_impl(def_id,
 112                                                   self.tcx.lang_items.const_ptr_impl(),
 113                                                   "const_ptr",
 114                                                   "*const T",
 115                                                   item.span);
 116                     }
 117                     ty::TyRawPtr(ty::TypeAndMut { ty: _, mutbl: hir::MutMutable }) => {
 118                         self.check_primitive_impl(def_id,
 119                                                   self.tcx.lang_items.mut_ptr_impl(),
 120                                                   "mut_ptr",
 121                                                   "*mut T",
 122                                                   item.span);
 123                     }
 124                     ty::TyInt(ast::TyI8) => {
 125                         self.check_primitive_impl(def_id,
 126                                                   self.tcx.lang_items.i8_impl(),
 127                                                   "i8",
 128                                                   "i8",
 129                                                   item.span);
 130                     }
 131                     ty::TyInt(ast::TyI16) => {
 132                         self.check_primitive_impl(def_id,
 133                                                   self.tcx.lang_items.i16_impl(),
 134                                                   "i16",
 135                                                   "i16",
 136                                                   item.span);
 137                     }
 138                     ty::TyInt(ast::TyI32) => {
 139                         self.check_primitive_impl(def_id,
 140                                                   self.tcx.lang_items.i32_impl(),
 141                                                   "i32",
 142                                                   "i32",
 143                                                   item.span);
 144                     }
 145                     ty::TyInt(ast::TyI64) => {
 146                         self.check_primitive_impl(def_id,
 147                                                   self.tcx.lang_items.i64_impl(),
 148                                                   "i64",
 149                                                   "i64",
 150                                                   item.span);
 151                     }
 152                     ty::TyInt(ast::TyIs) => {
 153                         self.check_primitive_impl(def_id,
 154                                                   self.tcx.lang_items.isize_impl(),
 155                                                   "isize",
 156                                                   "isize",
 157                                                   item.span);
 158                     }
 159                     ty::TyUint(ast::TyU8) => {
 160                         self.check_primitive_impl(def_id,
 161                                                   self.tcx.lang_items.u8_impl(),
 162                                                   "u8",
 163                                                   "u8",
 164                                                   item.span);
 165                     }
 166                     ty::TyUint(ast::TyU16) => {
 167                         self.check_primitive_impl(def_id,
 168                                                   self.tcx.lang_items.u16_impl(),
 169                                                   "u16",
 170                                                   "u16",
 171                                                   item.span);
 172                     }
 173                     ty::TyUint(ast::TyU32) => {
 174                         self.check_primitive_impl(def_id,
 175                                                   self.tcx.lang_items.u32_impl(),
 176                                                   "u32",
 177                                                   "u32",
 178                                                   item.span);
 179                     }
 180                     ty::TyUint(ast::TyU64) => {
 181                         self.check_primitive_impl(def_id,
 182                                                   self.tcx.lang_items.u64_impl(),
 183                                                   "u64",
 184                                                   "u64",
 185                                                   item.span);
 186                     }
 187                     ty::TyUint(ast::TyUs) => {
 188                         self.check_primitive_impl(def_id,
 189                                                   self.tcx.lang_items.usize_impl(),
 190                                                   "usize",
 191                                                   "usize",
 192                                                   item.span);
 193                     }
 194                     ty::TyFloat(ast::TyF32) => {
 195                         self.check_primitive_impl(def_id,
 196                                                   self.tcx.lang_items.f32_impl(),
 197                                                   "f32",
 198                                                   "f32",
 199                                                   item.span);
 200                     }
 201                     ty::TyFloat(ast::TyF64) => {
 202                         self.check_primitive_impl(def_id,
 203                                                   self.tcx.lang_items.f64_impl(),
 204                                                   "f64",
 205                                                   "f64",
 206                                                   item.span);
 207                     }
 208                     ty::TyError => {
 209                         return;
 210                     }
 211                     _ => {
 212                         span_err!(self.tcx.sess, item.span, E0118,
 213                                   "no base type found for inherent implementation; \
 214                                    implement a trait or new type instead");
 215                         return;
 216                     }
 217                 }
 218             }
 219             hir::ItemImpl(_, _, _, Some(_), _, _) => {
 220                 // "Trait" impl
 221                 debug!("coherence2::orphan check: trait impl {}",
 222                        self.tcx.map.node_to_string(item.id));
 223                 let trait_ref = self.tcx.impl_trait_ref(def_id).unwrap();
 224                 let trait_def_id = trait_ref.def_id;
 225                 match traits::orphan_check(self.tcx, def_id) {
 226                     Ok(()) => { }
 227                     Err(traits::OrphanCheckErr::NoLocalInputType) => {
 228                         span_err!(
 229                             self.tcx.sess, item.span, E0117,
 230                             "the impl does not reference any \
 231                              types defined in this crate; \
 232                              only traits defined in the current crate can be \
 233                              implemented for arbitrary types");
 234                         return;
 235                     }
 236                     Err(traits::OrphanCheckErr::UncoveredTy(param_ty)) => {
 237                         span_err!(self.tcx.sess, item.span, E0210,
 238                                 "type parameter `{}` must be used as the type parameter for \
 239                                  some local type (e.g. `MyStruct<T>`); only traits defined in \
 240                                  the current crate can be implemented for a type parameter",
 241                                 param_ty);
 242                         return;
 243                     }
 244                 }
 245
 246                 // In addition to the above rules, we restrict impls of defaulted traits
 247                 // so that they can only be implemented on structs/enums. To see why this
 248                 // restriction exists, consider the following example (#22978). Imagine
 249                 // that crate A defines a defaulted trait `Foo` and a fn that operates
 250                 // on pairs of types:
 251                 //
 252                 // ```
 253                 // // Crate A
 254                 // trait Foo { }
 255                 // impl Foo for .. { }
 256                 // fn two_foos<A:Foo,B:Foo>(..) {
 257                 //     one_foo::<(A,B)>(..)
 258                 // }
 259                 // fn one_foo<T:Foo>(..) { .. }
 260                 // ```
 261                 //
 262                 // This type-checks fine; in particular the fn
 263                 // `two_foos` is able to conclude that `(A,B):Foo`
 264                 // because `A:Foo` and `B:Foo`.
 265                 //
 266                 // Now imagine that crate B comes along and does the following:
 267                 //
 268                 // ```
 269                 // struct A { }
 270                 // struct B { }
 271                 // impl Foo for A { }
 272                 // impl Foo for B { }
 273                 // impl !Send for (A, B) { }
 274                 // ```
 275                 //
 276                 // This final impl is legal according to the orpan
 277                 // rules, but it invalidates the reasoning from
 278                 // `two_foos` above.
 279                 debug!("trait_ref={:?} trait_def_id={:?} trait_has_default_impl={}",
 280                        trait_ref,
 281                        trait_def_id,
 282                        self.tcx.trait_has_default_impl(trait_def_id));
 283                 if
 284                     self.tcx.trait_has_default_impl(trait_def_id) &&
 285                     trait_def_id.krate != LOCAL_CRATE
 286                 {
 287                     let self_ty = trait_ref.self_ty();
 288                     let opt_self_def_id = match self_ty.sty {
 289                         ty::TyStruct(self_def, _) | ty::TyEnum(self_def, _) =>
 290                             Some(self_def.did),
 291                         ty::TyBox(..) =>
 292                             self.tcx.lang_items.owned_box(),
 293                         _ =>
 294                             None
 295                     };
 296
 297                     let msg = match opt_self_def_id {
 298                         // We only want to permit structs/enums, but not *all* structs/enums.
 299                         // They must be local to the current crate, so that people
 300                         // can't do `unsafe impl Send for Rc<SomethingLocal>` or
 301                         // `impl !Send for Box<SomethingLocalAndSend>`.
 302                         Some(self_def_id) => {
 303                             if self_def_id.is_local() {
 304                                 None
 305                             } else {
 306                                 Some(format!(
 307                                     "cross-crate traits with a default impl, like `{}`, \
 308                                      can only be implemented for a struct/enum type \
 309                                      defined in the current crate",
 310                                     self.tcx.item_path_str(trait_def_id)))
 311                             }
 312                         }
 313                         _ => {
 314                             Some(format!(
 315                                 "cross-crate traits with a default impl, like `{}`, \
 316                                  can only be implemented for a struct/enum type, \
 317                                  not `{}`",
 318                                 self.tcx.item_path_str(trait_def_id),
 319                                 self_ty))
 320                         }
 321                     };
 322
 323                     if let Some(msg) = msg {
 324                         span_err!(self.tcx.sess, item.span, E0321, "{}", msg);
 325                         return;
 326                     }
 327                 }
 328
 329                 // Disallow *all* explicit impls of `Sized` and `Unsize` for now.
 330                 if Some(trait_def_id) == self.tcx.lang_items.sized_trait() {
 331                     span_err!(self.tcx.sess, item.span, E0322,
 332                               "explicit impls for the `Sized` trait are not permitted");
 333                     return;
 334                 }
 335                 if Some(trait_def_id) == self.tcx.lang_items.unsize_trait() {
 336                     span_err!(self.tcx.sess, item.span, E0328,
 337                               "explicit impls for the `Unsize` trait are not permitted");
 338                     return;
 339                 }
 340             }
 341             hir::ItemDefaultImpl(..) => {
 342                 // "Trait" impl
 343                 debug!("coherence2::orphan check: default trait impl {}",
 344                        self.tcx.map.node_to_string(item.id));
 345                 let trait_ref = self.tcx.impl_trait_ref(def_id).unwrap();
 346                 if trait_ref.def_id.krate != LOCAL_CRATE {
 347                     span_err!(self.tcx.sess, item.span, E0318,
 348                               "cannot create default implementations for traits outside the \
 349                                crate they're defined in; define a new trait instead");
 350                     return;
 351                 }
 352             }
 353             _ => {
 354                 // Not an impl
 355             }
 356         }
 357     }
 358 }
 359
 360 impl<'cx, 'tcx,'v> intravisit::Visitor<'v> for OrphanChecker<'cx, 'tcx> {
 361     fn visit_item(&mut self, item: &hir::Item) {
 362         self.check_item(item);
 363     }
 364 }