src/librustc/traits/mod.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 //! Trait Resolution. See the Book for more.
  12
  13 pub use self::SelectionError::*;
  14 pub use self::FulfillmentErrorCode::*;
  15 pub use self::Vtable::*;
  16 pub use self::ObligationCauseCode::*;
  17
  18 use hir::def_id::DefId;
  19 use middle::free_region::FreeRegionMap;
  20 use ty::subst;
  21 use ty::{self, Ty, TypeFoldable};
  22 use infer::{self, fixup_err_to_string, InferCtxt};
  23
  24 use std::rc::Rc;
  25 use syntax::ast;
  26 use syntax::codemap::{Span, DUMMY_SP};
  27
  28 pub use self::error_reporting::TraitErrorKey;
  29 pub use self::error_reporting::recursive_type_with_infinite_size_error;
  30 pub use self::error_reporting::report_fulfillment_errors;
  31 pub use self::error_reporting::report_overflow_error;
  32 pub use self::error_reporting::report_overflow_error_cycle;
  33 pub use self::error_reporting::report_selection_error;
  34 pub use self::error_reporting::report_object_safety_error;
  35 pub use self::coherence::orphan_check;
  36 pub use self::coherence::overlapping_impls;
  37 pub use self::coherence::OrphanCheckErr;
  38 pub use self::fulfill::{FulfillmentContext, GlobalFulfilledPredicates, RegionObligation};
  39 pub use self::project::{MismatchedProjectionTypes, ProjectionMode};
  40 pub use self::project::{normalize, Normalized};
  41 pub use self::object_safety::is_object_safe;
  42 pub use self::object_safety::astconv_object_safety_violations;
  43 pub use self::object_safety::object_safety_violations;
  44 pub use self::object_safety::ObjectSafetyViolation;
  45 pub use self::object_safety::MethodViolationCode;
  46 pub use self::object_safety::is_vtable_safe_method;
  47 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
  48 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
  49 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
  50 pub use self::specialize::{Overlap, specialization_graph, specializes, translate_substs};
  51 pub use self::util::elaborate_predicates;
  52 pub use self::util::get_vtable_index_of_object_method;
  53 pub use self::util::trait_ref_for_builtin_bound;
  54 pub use self::util::predicate_for_trait_def;
  55 pub use self::util::supertraits;
  56 pub use self::util::Supertraits;
  57 pub use self::util::supertrait_def_ids;
  58 pub use self::util::SupertraitDefIds;
  59 pub use self::util::transitive_bounds;
  60 pub use self::util::upcast;
  61
  62 mod coherence;
  63 mod error_reporting;
  64 mod fulfill;
  65 mod project;
  66 mod object_safety;
  67 mod select;
  68 mod specialize;
  69 mod structural_impls;
  70 mod util;
  71
  72 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
  73 /// which the vtable must be found.  The process of finding a vtable is
  74 /// called "resolving" the `Obligation`. This process consists of
  75 /// either identifying an `impl` (e.g., `impl Eq for int`) that
  76 /// provides the required vtable, or else finding a bound that is in
  77 /// scope. The eventual result is usually a `Selection` (defined below).
  78 #[derive(Clone, PartialEq, Eq)]
  79 pub struct Obligation<'tcx, T> {
  80     pub cause: ObligationCause<'tcx>,
  81     pub recursion_depth: usize,
  82     pub predicate: T,
  83 }
  84
  85 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
  86 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
  87
  88 /// Why did we incur this obligation? Used for error reporting.
  89 #[derive(Clone, Debug, PartialEq, Eq)]
  90 pub struct ObligationCause<'tcx> {
  91     pub span: Span,
  92
  93     // The id of the fn body that triggered this obligation. This is
  94     // used for region obligations to determine the precise
  95     // environment in which the region obligation should be evaluated
  96     // (in particular, closures can add new assumptions). See the
  97     // field `region_obligations` of the `FulfillmentContext` for more
  98     // information.
  99     pub body_id: ast::NodeId,
 100
 101     pub code: ObligationCauseCode<'tcx>
 102 }
 103
 104 #[derive(Clone, Debug, PartialEq, Eq)]
 105 pub enum ObligationCauseCode<'tcx> {
 106     /// Not well classified or should be obvious from span.
 107     MiscObligation,
 108
 109     /// This is the trait reference from the given projection
 110     SliceOrArrayElem,
 111
 112     /// This is the trait reference from the given projection
 113     ProjectionWf(ty::ProjectionTy<'tcx>),
 114
 115     /// In an impl of trait X for type Y, type Y must
 116     /// also implement all supertraits of X.
 117     ItemObligation(DefId),
 118
 119     /// A type like `&'a T` is WF only if `T: 'a`.
 120     ReferenceOutlivesReferent(Ty<'tcx>),
 121
 122     /// Obligation incurred due to an object cast.
 123     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 124
 125     /// Various cases where expressions must be sized/copy/etc:
 126     AssignmentLhsSized,        // L = X implies that L is Sized
 127     StructInitializerSized,    // S { ... } must be Sized
 128     VariableType(ast::NodeId), // Type of each variable must be Sized
 129     ReturnType,                // Return type must be Sized
 130     RepeatVec,                 // [T,..n] --> T must be Copy
 131
 132     // Captures of variable the given id by a closure (span is the
 133     // span of the closure)
 134     ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
 135
 136     // Types of fields (other than the last) in a struct must be sized.
 137     FieldSized,
 138
 139     // static items must have `Sync` type
 140     SharedStatic,
 141
 142     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 143
 144     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 145
 146     CompareImplMethodObligation,
 147 }
 148
 149 #[derive(Clone, Debug, PartialEq, Eq)]
 150 pub struct DerivedObligationCause<'tcx> {
 151     /// The trait reference of the parent obligation that led to the
 152     /// current obligation. Note that only trait obligations lead to
 153     /// derived obligations, so we just store the trait reference here
 154     /// directly.
 155     parent_trait_ref: ty::PolyTraitRef<'tcx>,
 156
 157     /// The parent trait had this cause
 158     parent_code: Rc<ObligationCauseCode<'tcx>>
 159 }
 160
 161 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
 162 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
 163 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
 164
 165 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
 166
 167 #[derive(Clone,Debug)]
 168 pub enum SelectionError<'tcx> {
 169     Unimplemented,
 170     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
 171                                 ty::PolyTraitRef<'tcx>,
 172                                 ty::error::TypeError<'tcx>),
 173     TraitNotObjectSafe(DefId),
 174 }
 175
 176 pub struct FulfillmentError<'tcx> {
 177     pub obligation: PredicateObligation<'tcx>,
 178     pub code: FulfillmentErrorCode<'tcx>
 179 }
 180
 181 #[derive(Clone)]
 182 pub enum FulfillmentErrorCode<'tcx> {
 183     CodeSelectionError(SelectionError<'tcx>),
 184     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
 185     CodeAmbiguity,
 186 }
 187
 188 /// When performing resolution, it is typically the case that there
 189 /// can be one of three outcomes:
 190 ///
 191 /// - `Ok(Some(r))`: success occurred with result `r`
 192 /// - `Ok(None)`: could not definitely determine anything, usually due
 193 ///   to inconclusive type inference.
 194 /// - `Err(e)`: error `e` occurred
 195 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 196
 197 /// Given the successful resolution of an obligation, the `Vtable`
 198 /// indicates where the vtable comes from. Note that while we call this
 199 /// a "vtable", it does not necessarily indicate dynamic dispatch at
 200 /// runtime. `Vtable` instances just tell the compiler where to find
 201 /// methods, but in generic code those methods are typically statically
 202 /// dispatched -- only when an object is constructed is a `Vtable`
 203 /// instance reified into an actual vtable.
 204 ///
 205 /// For example, the vtable may be tied to a specific impl (case A),
 206 /// or it may be relative to some bound that is in scope (case B).
 207 ///
 208 ///
 209 /// ```
 210 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 211 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 212 /// impl Clone for int { ... }             // Impl_3
 213 ///
 214 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
 215 ///                 param: T,
 216 ///                 mixed: Option<T>) {
 217 ///
 218 ///    // Case A: Vtable points at a specific impl. Only possible when
 219 ///    // type is concretely known. If the impl itself has bounded
 220 ///    // type parameters, Vtable will carry resolutions for those as well:
 221 ///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 222 ///
 223 ///    // Case B: Vtable must be provided by caller. This applies when
 224 ///    // type is a type parameter.
 225 ///    param.clone();    // VtableParam
 226 ///
 227 ///    // Case C: A mix of cases A and B.
 228 ///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
 229 /// }
 230 /// ```
 231 ///
 232 /// ### The type parameter `N`
 233 ///
 234 /// See explanation on `VtableImplData`.
 235 #[derive(Clone)]
 236 pub enum Vtable<'tcx, N> {
 237     /// Vtable identifying a particular impl.
 238     VtableImpl(VtableImplData<'tcx, N>),
 239
 240     /// Vtable for default trait implementations
 241     /// This carries the information and nested obligations with regards
 242     /// to a default implementation for a trait `Trait`. The nested obligations
 243     /// ensure the trait implementation holds for all the constituent types.
 244     VtableDefaultImpl(VtableDefaultImplData<N>),
 245
 246     /// Successful resolution to an obligation provided by the caller
 247     /// for some type parameter. The `Vec<N>` represents the
 248     /// obligations incurred from normalizing the where-clause (if
 249     /// any).
 250     VtableParam(Vec<N>),
 251
 252     /// Virtual calls through an object
 253     VtableObject(VtableObjectData<'tcx>),
 254
 255     /// Successful resolution for a builtin trait.
 256     VtableBuiltin(VtableBuiltinData<N>),
 257
 258     /// Vtable automatically generated for a closure. The def ID is the ID
 259     /// of the closure expression. This is a `VtableImpl` in spirit, but the
 260     /// impl is generated by the compiler and does not appear in the source.
 261     VtableClosure(VtableClosureData<'tcx, N>),
 262
 263     /// Same as above, but for a fn pointer type with the given signature.
 264     VtableFnPointer(ty::Ty<'tcx>),
 265 }
 266
 267 /// Identifies a particular impl in the source, along with a set of
 268 /// substitutions from the impl's type/lifetime parameters. The
 269 /// `nested` vector corresponds to the nested obligations attached to
 270 /// the impl's type parameters.
 271 ///
 272 /// The type parameter `N` indicates the type used for "nested
 273 /// obligations" that are required by the impl. During type check, this
 274 /// is `Obligation`, as one might expect. During trans, however, this
 275 /// is `()`, because trans only requires a shallow resolution of an
 276 /// impl, and nested obligations are satisfied later.
 277 #[derive(Clone, PartialEq, Eq)]
 278 pub struct VtableImplData<'tcx, N> {
 279     pub impl_def_id: DefId,
 280     pub substs: &'tcx subst::Substs<'tcx>,
 281     pub nested: Vec<N>
 282 }
 283
 284 #[derive(Clone, PartialEq, Eq)]
 285 pub struct VtableClosureData<'tcx, N> {
 286     pub closure_def_id: DefId,
 287     pub substs: ty::ClosureSubsts<'tcx>,
 288     /// Nested obligations. This can be non-empty if the closure
 289     /// signature contains associated types.
 290     pub nested: Vec<N>
 291 }
 292
 293 #[derive(Clone)]
 294 pub struct VtableDefaultImplData<N> {
 295     pub trait_def_id: DefId,
 296     pub nested: Vec<N>
 297 }
 298
 299 #[derive(Clone)]
 300 pub struct VtableBuiltinData<N> {
 301     pub nested: Vec<N>
 302 }
 303
 304 /// A vtable for some object-safe trait `Foo` automatically derived
 305 /// for the object type `Foo`.
 306 #[derive(PartialEq,Eq,Clone)]
 307 pub struct VtableObjectData<'tcx> {
 308     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 309     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 310
 311     /// The vtable is formed by concatenating together the method lists of
 312     /// the base object trait and all supertraits; this is the start of
 313     /// `upcast_trait_ref`'s methods in that vtable.
 314     pub vtable_base: usize
 315 }
 316
 317 /// Creates predicate obligations from the generic bounds.
 318 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 319                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 320                                      -> PredicateObligations<'tcx>
 321 {
 322     util::predicates_for_generics(cause, 0, generic_bounds)
 323 }
 324
 325 /// Determines whether the type `ty` is known to meet `bound` and
 326 /// returns true if so. Returns false if `ty` either does not meet
 327 /// `bound` or is not known to meet bound (note that this is
 328 /// conservative towards *no impl*, which is the opposite of the
 329 /// `evaluate` methods).
 330 pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
 331                                                  ty: Ty<'tcx>,
 332                                                  bound: ty::BuiltinBound,
 333                                                  span: Span)
 334                                                  -> bool
 335 {
 336     debug!("type_known_to_meet_builtin_bound(ty={:?}, bound={:?})",
 337            ty,
 338            bound);
 339
 340     let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 341     let obligation =
 342         util::predicate_for_builtin_bound(infcx.tcx, cause, bound, 0, ty);
 343     let obligation = match obligation {
 344         Ok(o) => o,
 345         Err(..) => return false
 346     };
 347     let result = SelectionContext::new(infcx)
 348         .evaluate_obligation_conservatively(&obligation);
 349     debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} => {:?}",
 350            ty, bound, result);
 351
 352     if result && (ty.has_infer_types() || ty.has_closure_types()) {
 353         // Because of inference "guessing", selection can sometimes claim
 354         // to succeed while the success requires a guess. To ensure
 355         // this function's result remains infallible, we must confirm
 356         // that guess. While imperfect, I believe this is sound.
 357
 358         let mut fulfill_cx = FulfillmentContext::new();
 359
 360         // We can use a dummy node-id here because we won't pay any mind
 361         // to region obligations that arise (there shouldn't really be any
 362         // anyhow).
 363         let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 364
 365         fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
 366
 367         // Note: we only assume something is `Copy` if we can
 368         // *definitively* show that it implements `Copy`. Otherwise,
 369         // assume it is move; linear is always ok.
 370         match fulfill_cx.select_all_or_error(infcx) {
 371             Ok(()) => {
 372                 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} success",
 373                        ty,
 374                        bound);
 375                 true
 376             }
 377             Err(e) => {
 378                 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} errors={:?}",
 379                        ty,
 380                        bound,
 381                        e);
 382                 false
 383             }
 384         }
 385     } else {
 386         result
 387     }
 388 }
 389
 390 // FIXME: this is gonna need to be removed ...
 391 /// Normalizes the parameter environment, reporting errors if they occur.
 392 pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
 393                                              cause: ObligationCause<'tcx>)
 394                                              -> ty::ParameterEnvironment<'a,'tcx>
 395 {
 396     // I'm not wild about reporting errors here; I'd prefer to
 397     // have the errors get reported at a defined place (e.g.,
 398     // during typeck). Instead I have all parameter
 399     // environments, in effect, going through this function
 400     // and hence potentially reporting errors. This ensurse of
 401     // course that we never forget to normalize (the
 402     // alternative seemed like it would involve a lot of
 403     // manual invocations of this fn -- and then we'd have to
 404     // deal with the errors at each of those sites).
 405     //
 406     // In any case, in practice, typeck constructs all the
 407     // parameter environments once for every fn as it goes,
 408     // and errors will get reported then; so after typeck we
 409     // can be sure that no errors should occur.
 410
 411     let tcx = unnormalized_env.tcx;
 412     let span = cause.span;
 413     let body_id = cause.body_id;
 414
 415     debug!("normalize_param_env_or_error(unnormalized_env={:?})",
 416            unnormalized_env);
 417
 418     let predicates: Vec<_> =
 419         util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.clone())
 420         .filter(|p| !p.is_global()) // (*)
 421         .collect();
 422
 423     // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
 424     // need to be in the *environment* to be proven, so screen those
 425     // out. This is important for the soundness of inter-fn
 426     // caching. Note though that we should probably check that these
 427     // predicates hold at the point where the environment is
 428     // constructed, but I am not currently doing so out of laziness.
 429     // -nmatsakis
 430
 431     debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
 432            predicates);
 433
 434     let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
 435
 436     let infcx = infer::new_infer_ctxt(tcx,
 437                                       &tcx.tables,
 438                                       Some(elaborated_env),
 439                                       ProjectionMode::AnyFinal);
 440     let predicates = match fully_normalize(&infcx,
 441                                            cause,
 442                                            &infcx.parameter_environment.caller_bounds) {
 443         Ok(predicates) => predicates,
 444         Err(errors) => {
 445             report_fulfillment_errors(&infcx, &errors);
 446             return infcx.parameter_environment; // an unnormalized env is better than nothing
 447         }
 448     };
 449
 450     debug!("normalize_param_env_or_error: normalized predicates={:?}",
 451            predicates);
 452
 453     let free_regions = FreeRegionMap::new();
 454     infcx.resolve_regions_and_report_errors(&free_regions, body_id);
 455     let predicates = match infcx.fully_resolve(&predicates) {
 456         Ok(predicates) => predicates,
 457         Err(fixup_err) => {
 458             // If we encounter a fixup error, it means that some type
 459             // variable wound up unconstrained. I actually don't know
 460             // if this can happen, and I certainly don't expect it to
 461             // happen often, but if it did happen it probably
 462             // represents a legitimate failure due to some kind of
 463             // unconstrained variable, and it seems better not to ICE,
 464             // all things considered.
 465             let err_msg = fixup_err_to_string(fixup_err);
 466             tcx.sess.span_err(span, &err_msg);
 467             return infcx.parameter_environment; // an unnormalized env is better than nothing
 468         }
 469     };
 470
 471     debug!("normalize_param_env_or_error: resolved predicates={:?}",
 472            predicates);
 473
 474     infcx.parameter_environment.with_caller_bounds(predicates)
 475 }
 476
 477 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
 478                                   cause: ObligationCause<'tcx>,
 479                                   value: &T)
 480                                   -> Result<T, Vec<FulfillmentError<'tcx>>>
 481     where T : TypeFoldable<'tcx>
 482 {
 483     debug!("fully_normalize(value={:?})", value);
 484
 485     let mut selcx = &mut SelectionContext::new(infcx);
 486     // FIXME (@jroesch) ISSUE 26721
 487     // I'm not sure if this is a bug or not, needs further investigation.
 488     // It appears that by reusing the fulfillment_cx here we incur more
 489     // obligations and later trip an asssertion on regionck.rs line 337.
 490     //
 491     // The two possibilities I see is:
 492     //      - normalization is not actually fully happening and we
 493     //        have a bug else where
 494     //      - we are adding a duplicate bound into the list causing
 495     //        its size to change.
 496     //
 497     // I think we should probably land this refactor and then come
 498     // back to this is a follow-up patch.
 499     let mut fulfill_cx = FulfillmentContext::new();
 500
 501     let Normalized { value: normalized_value, obligations } =
 502         project::normalize(selcx, cause, value);
 503     debug!("fully_normalize: normalized_value={:?} obligations={:?}",
 504            normalized_value,
 505            obligations);
 506     for obligation in obligations {
 507         fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
 508     }
 509
 510     debug!("fully_normalize: select_all_or_error start");
 511     match fulfill_cx.select_all_or_error(infcx) {
 512         Ok(()) => { }
 513         Err(e) => {
 514             debug!("fully_normalize: error={:?}", e);
 515             return Err(e);
 516         }
 517     }
 518     debug!("fully_normalize: select_all_or_error complete");
 519     let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
 520     debug!("fully_normalize: resolved_value={:?}", resolved_value);
 521     Ok(resolved_value)
 522 }
 523
 524 impl<'tcx,O> Obligation<'tcx,O> {
 525     pub fn new(cause: ObligationCause<'tcx>,
 526                trait_ref: O)
 527                -> Obligation<'tcx, O>
 528     {
 529         Obligation { cause: cause,
 530                      recursion_depth: 0,
 531                      predicate: trait_ref }
 532     }
 533
 534     fn with_depth(cause: ObligationCause<'tcx>,
 535                   recursion_depth: usize,
 536                   trait_ref: O)
 537                   -> Obligation<'tcx, O>
 538     {
 539         Obligation { cause: cause,
 540                      recursion_depth: recursion_depth,
 541                      predicate: trait_ref }
 542     }
 543
 544     pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
 545         Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
 546     }
 547
 548     pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
 549         Obligation { cause: self.cause.clone(),
 550                      recursion_depth: self.recursion_depth,
 551                      predicate: value }
 552     }
 553 }
 554
 555 impl<'tcx> ObligationCause<'tcx> {
 556     pub fn new(span: Span,
 557                body_id: ast::NodeId,
 558                code: ObligationCauseCode<'tcx>)
 559                -> ObligationCause<'tcx> {
 560         ObligationCause { span: span, body_id: body_id, code: code }
 561     }
 562
 563     pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
 564         ObligationCause { span: span, body_id: body_id, code: MiscObligation }
 565     }
 566
 567     pub fn dummy() -> ObligationCause<'tcx> {
 568         ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
 569     }
 570 }
 571
 572 impl<'tcx, N> Vtable<'tcx, N> {
 573     pub fn nested_obligations(self) -> Vec<N> {
 574         match self {
 575             VtableImpl(i) => i.nested,
 576             VtableParam(n) => n,
 577             VtableBuiltin(i) => i.nested,
 578             VtableDefaultImpl(d) => d.nested,
 579             VtableClosure(c) => c.nested,
 580             VtableObject(_) | VtableFnPointer(..) => vec![]
 581         }
 582     }
 583
 584     pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
 585         match self {
 586             VtableImpl(i) => VtableImpl(VtableImplData {
 587                 impl_def_id: i.impl_def_id,
 588                 substs: i.substs,
 589                 nested: i.nested.into_iter().map(f).collect()
 590             }),
 591             VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
 592             VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
 593                 nested: i.nested.into_iter().map(f).collect()
 594             }),
 595             VtableObject(o) => VtableObject(o),
 596             VtableDefaultImpl(d) => VtableDefaultImpl(VtableDefaultImplData {
 597                 trait_def_id: d.trait_def_id,
 598                 nested: d.nested.into_iter().map(f).collect()
 599             }),
 600             VtableFnPointer(f) => VtableFnPointer(f),
 601             VtableClosure(c) => VtableClosure(VtableClosureData {
 602                 closure_def_id: c.closure_def_id,
 603                 substs: c.substs,
 604                 nested: c.nested.into_iter().map(f).collect(),
 605             })
 606         }
 607     }
 608 }
 609
 610 impl<'tcx> FulfillmentError<'tcx> {
 611     fn new(obligation: PredicateObligation<'tcx>,
 612            code: FulfillmentErrorCode<'tcx>)
 613            -> FulfillmentError<'tcx>
 614     {
 615         FulfillmentError { obligation: obligation, code: code }
 616     }
 617 }
 618
 619 impl<'tcx> TraitObligation<'tcx> {
 620     fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
 621         ty::Binder(self.predicate.skip_binder().self_ty())
 622     }
 623 }