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