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::lang_items::UnsizeTraitLangItem;
  16
  17 use rustc::traits::{self, ObligationCause, Reveal};
  18 use rustc::ty::{self, Ty, TyCtxt};
  19 use rustc::ty::ParameterEnvironment;
  20 use rustc::ty::TypeFoldable;
  21 use rustc::ty::subst::Subst;
  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.item_type(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, &format!("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.item_type(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 = ParameterEnvironment::for_item(tcx, impl_node_id);
 109     let self_type = self_type.subst(tcx, &param_env.free_substs);
 110     assert!(!self_type.has_escaping_regions());
 111
 112     debug!("visit_implementation_of_copy: self_type={:?} (free)",
 113            self_type);
 114
 115     match param_env.can_type_implement_copy(tcx, self_type, span) {
 116         Ok(()) => {}
 117         Err(CopyImplementationError::InfrigingField(field)) => {
 118             let item = tcx.hir.expect_item(impl_node_id);
 119             let span = if let ItemImpl(.., Some(ref tr), _, _) = item.node {
 120                 tr.path.span
 121             } else {
 122                 span
 123             };
 124
 125             struct_span_err!(tcx.sess,
 126                              span,
 127                              E0204,
 128                              "the trait `Copy` may not be implemented for this type")
 129                 .span_label(
 130                     tcx.def_span(field.did),
 131                     &"this field does not implement `Copy`")
 132                 .emit()
 133         }
 134         Err(CopyImplementationError::NotAnAdt) => {
 135             let item = tcx.hir.expect_item(impl_node_id);
 136             let span = if let ItemImpl(.., ref ty, _) = item.node {
 137                 ty.span
 138             } else {
 139                 span
 140             };
 141
 142             struct_span_err!(tcx.sess,
 143                              span,
 144                              E0206,
 145                              "the trait `Copy` may not be implemented for this type")
 146                 .span_label(span, &format!("type is not a structure or enumeration"))
 147                 .emit();
 148         }
 149         Err(CopyImplementationError::HasDestructor) => {
 150             struct_span_err!(tcx.sess,
 151                              span,
 152                              E0184,
 153                              "the trait `Copy` may not be implemented for this type; the \
 154                               type has a destructor")
 155                 .span_label(span, &format!("Copy not allowed on types with destructors"))
 156                 .emit();
 157         }
 158     }
 159 }
 160
 161 fn visit_implementation_of_coerce_unsized<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 162                                                     coerce_unsized_trait: DefId,
 163                                                     impl_did: DefId) {
 164     debug!("visit_implementation_of_coerce_unsized: impl_did={:?}",
 165            impl_did);
 166
 167     let unsize_trait = match tcx.lang_items.require(UnsizeTraitLangItem) {
 168         Ok(id) => id,
 169         Err(err) => {
 170             tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
 171         }
 172     };
 173
 174     let impl_node_id = if let Some(n) = tcx.hir.as_local_node_id(impl_did) {
 175         n
 176     } else {
 177         debug!("visit_implementation_of_coerce_unsized(): impl not \
 178                 in this crate");
 179         return;
 180     };
 181
 182     let source = tcx.item_type(impl_did);
 183     let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
 184     let target = trait_ref.substs.type_at(1);
 185     debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)",
 186            source,
 187            target);
 188
 189     let span = tcx.hir.span(impl_node_id);
 190     let param_env = ParameterEnvironment::for_item(tcx, impl_node_id);
 191     let source = source.subst(tcx, &param_env.free_substs);
 192     let target = target.subst(tcx, &param_env.free_substs);
 193     assert!(!source.has_escaping_regions());
 194
 195     debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)",
 196            source,
 197            target);
 198
 199     tcx.infer_ctxt(param_env, Reveal::UserFacing).enter(|infcx| {
 200         let cause = ObligationCause::misc(span, impl_node_id);
 201         let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
 202                            mt_b: ty::TypeAndMut<'tcx>,
 203                            mk_ptr: &Fn(Ty<'tcx>) -> Ty<'tcx>| {
 204             if (mt_a.mutbl, mt_b.mutbl) == (hir::MutImmutable, hir::MutMutable) {
 205                 infcx.report_mismatched_types(&cause,
 206                                              mk_ptr(mt_b.ty),
 207                                              target,
 208                                              ty::error::TypeError::Mutability)
 209                     .emit();
 210             }
 211             (mt_a.ty, mt_b.ty, unsize_trait, None)
 212         };
 213         let (source, target, trait_def_id, kind) = match (&source.sty, &target.sty) {
 214             (&ty::TyRef(r_a, mt_a), &ty::TyRef(r_b, mt_b)) => {
 215                 infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
 216                 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
 217             }
 218
 219             (&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) |
 220             (&ty::TyRawPtr(mt_a), &ty::TyRawPtr(mt_b)) => {
 221                 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
 222             }
 223
 224             (&ty::TyAdt(def_a, substs_a), &ty::TyAdt(def_b, substs_b)) if def_a.is_struct() &&
 225                                                                           def_b.is_struct() => {
 226                 if def_a != def_b {
 227                     let source_path = tcx.item_path_str(def_a.did);
 228                     let target_path = tcx.item_path_str(def_b.did);
 229                     span_err!(tcx.sess,
 230                               span,
 231                               E0377,
 232                               "the trait `CoerceUnsized` may only be implemented \
 233                                for a coercion between structures with the same \
 234                                definition; expected {}, found {}",
 235                               source_path,
 236                               target_path);
 237                     return;
 238                 }
 239
 240                 let fields = &def_a.struct_variant().fields;
 241                 let diff_fields = fields.iter()
 242                     .enumerate()
 243                     .filter_map(|(i, f)| {
 244                         let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
 245
 246                         if tcx.item_type(f.did).is_phantom_data() {
 247                             // Ignore PhantomData fields
 248                             return None;
 249                         }
 250
 251                         // Ignore fields that aren't significantly changed
 252                         if let Ok(ok) = infcx.sub_types(false, &cause, b, a) {
 253                             if ok.obligations.is_empty() {
 254                                 return None;
 255                             }
 256                         }
 257
 258                         // Collect up all fields that were significantly changed
 259                         // i.e. those that contain T in coerce_unsized T -> U
 260                         Some((i, a, b))
 261                     })
 262                     .collect::<Vec<_>>();
 263
 264                 if diff_fields.is_empty() {
 265                     span_err!(tcx.sess,
 266                               span,
 267                               E0374,
 268                               "the trait `CoerceUnsized` may only be implemented \
 269                                for a coercion between structures with one field \
 270                                being coerced, none found");
 271                     return;
 272                 } else if diff_fields.len() > 1 {
 273                     let item = tcx.hir.expect_item(impl_node_id);
 274                     let span = if let ItemImpl(.., Some(ref t), _, _) = item.node {
 275                         t.path.span
 276                     } else {
 277                         tcx.hir.span(impl_node_id)
 278                     };
 279
 280                     let mut err = struct_span_err!(tcx.sess,
 281                                                    span,
 282                                                    E0375,
 283                                                    "implementing the trait \
 284                                                     `CoerceUnsized` requires multiple \
 285                                                     coercions");
 286                     err.note("`CoerceUnsized` may only be implemented for \
 287                               a coercion between structures with one field being coerced");
 288                     err.note(&format!("currently, {} fields need coercions: {}",
 289                                       diff_fields.len(),
 290                                       diff_fields.iter()
 291                                           .map(|&(i, a, b)| {
 292                                               format!("{} ({} to {})", fields[i].name, a, b)
 293                                           })
 294                                           .collect::<Vec<_>>()
 295                                           .join(", ")));
 296                     err.span_label(span, &format!("requires multiple coercions"));
 297                     err.emit();
 298                     return;
 299                 }
 300
 301                 let (i, a, b) = diff_fields[0];
 302                 let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
 303                 (a, b, coerce_unsized_trait, Some(kind))
 304             }
 305
 306             _ => {
 307                 span_err!(tcx.sess,
 308                           span,
 309                           E0376,
 310                           "the trait `CoerceUnsized` may only be implemented \
 311                            for a coercion between structures");
 312                 return;
 313             }
 314         };
 315
 316         let mut fulfill_cx = traits::FulfillmentContext::new();
 317
 318         // Register an obligation for `A: Trait<B>`.
 319         let cause = traits::ObligationCause::misc(span, impl_node_id);
 320         let predicate = tcx.predicate_for_trait_def(cause, trait_def_id, 0, source, &[target]);
 321         fulfill_cx.register_predicate_obligation(&infcx, predicate);
 322
 323         // Check that all transitive obligations are satisfied.
 324         if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
 325             infcx.report_fulfillment_errors(&errors);
 326         }
 327
 328         // Finally, resolve all regions.
 329         let mut free_regions = FreeRegionMap::new();
 330         free_regions.relate_free_regions_from_predicates(&infcx.parameter_environment
 331             .caller_bounds);
 332         infcx.resolve_regions_and_report_errors(&free_regions, impl_node_id);
 333
 334         if let Some(kind) = kind {
 335             tcx.maps.custom_coerce_unsized_kind.borrow_mut().insert(impl_did, kind);
 336         }
 337     });
 338 }