src/librustc_typeck/coherence/builtin.rs

   1 // Copyright 2016 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 //! Check properties that are required by built-in traits and set
  12 //! up data structures required by type-checking/translation.
  13
  14 use rustc::middle::free_region::FreeRegionMap;
  15 use rustc::middle::region::RegionMaps;
  16 use rustc::middle::lang_items::UnsizeTraitLangItem;
  17
  18 use rustc::traits::{self, ObligationCause, Reveal};
  19 use rustc::ty::{self, Ty, TyCtxt};
  20 use rustc::ty::ParameterEnvironment;
  21 use rustc::ty::TypeFoldable;
  22 use rustc::ty::adjustment::CoerceUnsizedInfo;
  23 use rustc::ty::subst::Subst;
  24 use rustc::ty::util::CopyImplementationError;
  25 use rustc::infer;
  26
  27 use rustc::hir::def_id::DefId;
  28 use rustc::hir::map as hir_map;
  29 use rustc::hir::{self, ItemImpl};
  30
  31 pub fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, trait_def_id: DefId) {
  32     Checker { tcx, trait_def_id }
  33         .check(tcx.lang_items.drop_trait(), visit_implementation_of_drop)
  34         .check(tcx.lang_items.copy_trait(), visit_implementation_of_copy)
  35         .check(tcx.lang_items.coerce_unsized_trait(),
  36                visit_implementation_of_coerce_unsized);
  37 }
  38
  39 struct Checker<'a, 'tcx: 'a> {
  40     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  41     trait_def_id: DefId
  42 }
  43
  44 impl<'a, 'tcx> Checker<'a, 'tcx> {
  45     fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self
  46         where F: FnMut(TyCtxt<'a, 'tcx, 'tcx>, DefId, DefId)
  47     {
  48         if Some(self.trait_def_id) == trait_def_id {
  49             for &impl_id in self.tcx.hir.trait_impls(self.trait_def_id) {
  50                 let impl_def_id = self.tcx.hir.local_def_id(impl_id);
  51                 f(self.tcx, self.trait_def_id, impl_def_id);
  52             }
  53         }
  54         self
  55     }
  56 }
  57
  58 fn visit_implementation_of_drop<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  59                                           _drop_did: DefId,
  60                                           impl_did: DefId) {
  61     match tcx.type_of(impl_did).sty {
  62         ty::TyAdt(..) => {}
  63         _ => {
  64             // Destructors only work on nominal types.
  65             if let Some(impl_node_id) = tcx.hir.as_local_node_id(impl_did) {
  66                 match tcx.hir.find(impl_node_id) {
  67                     Some(hir_map::NodeItem(item)) => {
  68                         let span = match item.node {
  69                             ItemImpl(.., ref ty, _) => ty.span,
  70                             _ => item.span,
  71                         };
  72                         struct_span_err!(tcx.sess,
  73                                          span,
  74                                          E0120,
  75                                          "the Drop trait may only be implemented on \
  76                                          structures")
  77                             .span_label(span, "implementing Drop requires a struct")
  78                             .emit();
  79                     }
  80                     _ => {
  81                         bug!("didn't find impl in ast map");
  82                     }
  83                 }
  84             } else {
  85                 bug!("found external impl of Drop trait on \
  86                       something other than a struct");
  87             }
  88         }
  89     }
  90 }
  91
  92 fn visit_implementation_of_copy<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  93                                           _copy_did: DefId,
  94                                           impl_did: DefId) {
  95     debug!("visit_implementation_of_copy: impl_did={:?}", impl_did);
  96
  97     let impl_node_id = if let Some(n) = tcx.hir.as_local_node_id(impl_did) {
  98         n
  99     } else {
 100         debug!("visit_implementation_of_copy(): impl not in this \
 101                 crate");
 102         return;
 103     };
 104
 105     let self_type = tcx.type_of(impl_did);
 106     debug!("visit_implementation_of_copy: self_type={:?} (bound)",
 107            self_type);
 108
 109     let span = tcx.hir.span(impl_node_id);
 110     let param_env = ParameterEnvironment::for_item(tcx, impl_node_id);
 111     let self_type = self_type.subst(tcx, &param_env.free_substs);
 112     assert!(!self_type.has_escaping_regions());
 113
 114     debug!("visit_implementation_of_copy: self_type={:?} (free)",
 115            self_type);
 116
 117     match param_env.can_type_implement_copy(tcx, self_type, span) {
 118         Ok(()) => {}
 119         Err(CopyImplementationError::InfrigingField(field)) => {
 120             let item = tcx.hir.expect_item(impl_node_id);
 121             let span = if let ItemImpl(.., Some(ref tr), _, _) = item.node {
 122                 tr.path.span
 123             } else {
 124                 span
 125             };
 126
 127             struct_span_err!(tcx.sess,
 128                              span,
 129                              E0204,
 130                              "the trait `Copy` may not be implemented for this type")
 131                 .span_label(
 132                     tcx.def_span(field.did),
 133                     "this field does not implement `Copy`")
 134                 .emit()
 135         }
 136         Err(CopyImplementationError::NotAnAdt) => {
 137             let item = tcx.hir.expect_item(impl_node_id);
 138             let span = if let ItemImpl(.., ref ty, _) = item.node {
 139                 ty.span
 140             } else {
 141                 span
 142             };
 143
 144             struct_span_err!(tcx.sess,
 145                              span,
 146                              E0206,
 147                              "the trait `Copy` may not be implemented for this type")
 148                 .span_label(span, "type is not a structure or enumeration")
 149                 .emit();
 150         }
 151         Err(CopyImplementationError::HasDestructor) => {
 152             struct_span_err!(tcx.sess,
 153                              span,
 154                              E0184,
 155                              "the trait `Copy` may not be implemented for this type; the \
 156                               type has a destructor")
 157                 .span_label(span, "Copy not allowed on types with destructors")
 158                 .emit();
 159         }
 160     }
 161 }
 162
 163 fn visit_implementation_of_coerce_unsized<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 164                                                     _: DefId,
 165                                                     impl_did: DefId) {
 166     debug!("visit_implementation_of_coerce_unsized: impl_did={:?}",
 167            impl_did);
 168
 169     // Just compute this for the side-effects, in particular reporting
 170     // errors; other parts of the code may demand it for the info of
 171     // course.
 172     if impl_did.is_local() {
 173         let span = tcx.def_span(impl_did);
 174         tcx.at(span).coerce_unsized_info(impl_did);
 175     }
 176 }
 177
 178 pub fn coerce_unsized_info<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 179                                      impl_did: DefId)
 180                                      -> CoerceUnsizedInfo {
 181     debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did);
 182     let coerce_unsized_trait = tcx.lang_items.coerce_unsized_trait().unwrap();
 183
 184     let unsize_trait = match tcx.lang_items.require(UnsizeTraitLangItem) {
 185         Ok(id) => id,
 186         Err(err) => {
 187             tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
 188         }
 189     };
 190
 191     // this provider should only get invoked for local def-ids
 192     let impl_node_id = tcx.hir.as_local_node_id(impl_did).unwrap_or_else(|| {
 193         bug!("coerce_unsized_info: invoked for non-local def-id {:?}", impl_did)
 194     });
 195
 196     let source = tcx.type_of(impl_did);
 197     let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
 198     assert_eq!(trait_ref.def_id, coerce_unsized_trait);
 199     let target = trait_ref.substs.type_at(1);
 200     debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)",
 201            source,
 202            target);
 203
 204     let span = tcx.hir.span(impl_node_id);
 205     let param_env = ParameterEnvironment::for_item(tcx, impl_node_id);
 206     let source = source.subst(tcx, &param_env.free_substs);
 207     let target = target.subst(tcx, &param_env.free_substs);
 208     assert!(!source.has_escaping_regions());
 209
 210     let err_info = CoerceUnsizedInfo { custom_kind: None };
 211
 212     debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)",
 213            source,
 214            target);
 215
 216     tcx.infer_ctxt(param_env, Reveal::UserFacing).enter(|infcx| {
 217         let cause = ObligationCause::misc(span, impl_node_id);
 218         let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
 219                            mt_b: ty::TypeAndMut<'tcx>,
 220                            mk_ptr: &Fn(Ty<'tcx>) -> Ty<'tcx>| {
 221             if (mt_a.mutbl, mt_b.mutbl) == (hir::MutImmutable, hir::MutMutable) {
 222                 infcx.report_mismatched_types(&cause,
 223                                              mk_ptr(mt_b.ty),
 224                                              target,
 225                                              ty::error::TypeError::Mutability)
 226                     .emit();
 227             }
 228             (mt_a.ty, mt_b.ty, unsize_trait, None)
 229         };
 230         let (source, target, trait_def_id, kind) = match (&source.sty, &target.sty) {
 231             (&ty::TyRef(r_a, mt_a), &ty::TyRef(r_b, mt_b)) => {
 232                 infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
 233                 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
 234             }
 235
 236             (&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) |
 237             (&ty::TyRawPtr(mt_a), &ty::TyRawPtr(mt_b)) => {
 238                 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
 239             }
 240
 241             (&ty::TyAdt(def_a, substs_a), &ty::TyAdt(def_b, substs_b)) if def_a.is_struct() &&
 242                                                                           def_b.is_struct() => {
 243                 if def_a != def_b {
 244                     let source_path = tcx.item_path_str(def_a.did);
 245                     let target_path = tcx.item_path_str(def_b.did);
 246                     span_err!(tcx.sess,
 247                               span,
 248                               E0377,
 249                               "the trait `CoerceUnsized` may only be implemented \
 250                                for a coercion between structures with the same \
 251                                definition; expected {}, found {}",
 252                               source_path,
 253                               target_path);
 254                     return err_info;
 255                 }
 256
 257                 let fields = &def_a.struct_variant().fields;
 258                 let diff_fields = fields.iter()
 259                     .enumerate()
 260                     .filter_map(|(i, f)| {
 261                         let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
 262
 263                         if tcx.type_of(f.did).is_phantom_data() {
 264                             // Ignore PhantomData fields
 265                             return None;
 266                         }
 267
 268                         // Ignore fields that aren't significantly changed
 269                         if let Ok(ok) = infcx.sub_types(false, &cause, b, a) {
 270                             if ok.obligations.is_empty() {
 271                                 return None;
 272                             }
 273                         }
 274
 275                         // Collect up all fields that were significantly changed
 276                         // i.e. those that contain T in coerce_unsized T -> U
 277                         Some((i, a, b))
 278                     })
 279                     .collect::<Vec<_>>();
 280
 281                 if diff_fields.is_empty() {
 282                     span_err!(tcx.sess,
 283                               span,
 284                               E0374,
 285                               "the trait `CoerceUnsized` may only be implemented \
 286                                for a coercion between structures with one field \
 287                                being coerced, none found");
 288                     return err_info;
 289                 } else if diff_fields.len() > 1 {
 290                     let item = tcx.hir.expect_item(impl_node_id);
 291                     let span = if let ItemImpl(.., Some(ref t), _, _) = item.node {
 292                         t.path.span
 293                     } else {
 294                         tcx.hir.span(impl_node_id)
 295                     };
 296
 297                     let mut err = struct_span_err!(tcx.sess,
 298                                                    span,
 299                                                    E0375,
 300                                                    "implementing the trait \
 301                                                     `CoerceUnsized` requires multiple \
 302                                                     coercions");
 303                     err.note("`CoerceUnsized` may only be implemented for \
 304                               a coercion between structures with one field being coerced");
 305                     err.note(&format!("currently, {} fields need coercions: {}",
 306                                       diff_fields.len(),
 307                                       diff_fields.iter()
 308                                           .map(|&(i, a, b)| {
 309                                               format!("{} ({} to {})", fields[i].name, a, b)
 310                                           })
 311                                           .collect::<Vec<_>>()
 312                                           .join(", ")));
 313                     err.span_label(span, "requires multiple coercions");
 314                     err.emit();
 315                     return err_info;
 316                 }
 317
 318                 let (i, a, b) = diff_fields[0];
 319                 let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
 320                 (a, b, coerce_unsized_trait, Some(kind))
 321             }
 322
 323             _ => {
 324                 span_err!(tcx.sess,
 325                           span,
 326                           E0376,
 327                           "the trait `CoerceUnsized` may only be implemented \
 328                            for a coercion between structures");
 329                 return err_info;
 330             }
 331         };
 332
 333         let mut fulfill_cx = traits::FulfillmentContext::new();
 334
 335         // Register an obligation for `A: Trait<B>`.
 336         let cause = traits::ObligationCause::misc(span, impl_node_id);
 337         let predicate = tcx.predicate_for_trait_def(cause, trait_def_id, 0, source, &[target]);
 338         fulfill_cx.register_predicate_obligation(&infcx, predicate);
 339
 340         // Check that all transitive obligations are satisfied.
 341         if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
 342             infcx.report_fulfillment_errors(&errors);
 343         }
 344
 345         // Finally, resolve all regions.
 346         let region_maps = RegionMaps::new();
 347         let mut free_regions = FreeRegionMap::new();
 348         free_regions.relate_free_regions_from_predicates(&infcx.parameter_environment
 349             .caller_bounds);
 350         infcx.resolve_regions_and_report_errors(impl_did, &region_maps, &free_regions);
 351
 352         CoerceUnsizedInfo {
 353             custom_kind: kind
 354         }
 355     })
 356 }