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 README.md for an overview of how this works.
  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, TyCtxt, TypeFoldable};
  22 use infer::InferCtxt;
  23
  24 use std::rc::Rc;
  25 use syntax::ast;
  26 use syntax_pos::{Span, DUMMY_SP};
  27
  28 pub use self::error_reporting::TraitErrorKey;
  29 pub use self::coherence::orphan_check;
  30 pub use self::coherence::overlapping_impls;
  31 pub use self::coherence::OrphanCheckErr;
  32 pub use self::fulfill::{FulfillmentContext, GlobalFulfilledPredicates, RegionObligation};
  33 pub use self::project::MismatchedProjectionTypes;
  34 pub use self::project::{normalize, normalize_projection_type, Normalized};
  35 pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, ProjectionMode};
  36 pub use self::object_safety::ObjectSafetyViolation;
  37 pub use self::object_safety::MethodViolationCode;
  38 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
  39 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
  40 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
  41 pub use self::specialize::{OverlapError, specialization_graph, specializes, translate_substs};
  42 pub use self::specialize::{SpecializesCache};
  43 pub use self::util::elaborate_predicates;
  44 pub use self::util::supertraits;
  45 pub use self::util::Supertraits;
  46 pub use self::util::supertrait_def_ids;
  47 pub use self::util::SupertraitDefIds;
  48 pub use self::util::transitive_bounds;
  49
  50 mod coherence;
  51 mod error_reporting;
  52 mod fulfill;
  53 mod project;
  54 mod object_safety;
  55 mod select;
  56 mod specialize;
  57 mod structural_impls;
  58 mod util;
  59
  60 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
  61 /// which the vtable must be found.  The process of finding a vtable is
  62 /// called "resolving" the `Obligation`. This process consists of
  63 /// either identifying an `impl` (e.g., `impl Eq for int`) that
  64 /// provides the required vtable, or else finding a bound that is in
  65 /// scope. The eventual result is usually a `Selection` (defined below).
  66 #[derive(Clone, PartialEq, Eq)]
  67 pub struct Obligation<'tcx, T> {
  68     pub cause: ObligationCause<'tcx>,
  69     pub recursion_depth: usize,
  70     pub predicate: T,
  71 }
  72
  73 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
  74 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
  75
  76 /// Why did we incur this obligation? Used for error reporting.
  77 #[derive(Clone, Debug, PartialEq, Eq)]
  78 pub struct ObligationCause<'tcx> {
  79     pub span: Span,
  80
  81     // The id of the fn body that triggered this obligation. This is
  82     // used for region obligations to determine the precise
  83     // environment in which the region obligation should be evaluated
  84     // (in particular, closures can add new assumptions). See the
  85     // field `region_obligations` of the `FulfillmentContext` for more
  86     // information.
  87     pub body_id: ast::NodeId,
  88
  89     pub code: ObligationCauseCode<'tcx>
  90 }
  91
  92 #[derive(Clone, Debug, PartialEq, Eq)]
  93 pub enum ObligationCauseCode<'tcx> {
  94     /// Not well classified or should be obvious from span.
  95     MiscObligation,
  96
  97     /// A slice or array is WF only if `T: Sized`
  98     SliceOrArrayElem,
  99
 100     /// A tuple is WF only if its middle elements are Sized
 101     TupleElem,
 102
 103     /// This is the trait reference from the given projection
 104     ProjectionWf(ty::ProjectionTy<'tcx>),
 105
 106     /// In an impl of trait X for type Y, type Y must
 107     /// also implement all supertraits of X.
 108     ItemObligation(DefId),
 109
 110     /// A type like `&'a T` is WF only if `T: 'a`.
 111     ReferenceOutlivesReferent(Ty<'tcx>),
 112
 113     /// Obligation incurred due to an object cast.
 114     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 115
 116     /// Various cases where expressions must be sized/copy/etc:
 117     AssignmentLhsSized,        // L = X implies that L is Sized
 118     StructInitializerSized,    // S { ... } must be Sized
 119     VariableType(ast::NodeId), // Type of each variable must be Sized
 120     ReturnType,                // Return type must be Sized
 121     RepeatVec,                 // [T,..n] --> T must be Copy
 122
 123     // Captures of variable the given id by a closure (span is the
 124     // span of the closure)
 125     ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
 126
 127     // Types of fields (other than the last) in a struct must be sized.
 128     FieldSized,
 129
 130     // Constant expressions must be sized.
 131     ConstSized,
 132
 133     // static items must have `Sync` type
 134     SharedStatic,
 135
 136     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 137
 138     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 139
 140     CompareImplMethodObligation,
 141 }
 142
 143 #[derive(Clone, Debug, PartialEq, Eq)]
 144 pub struct DerivedObligationCause<'tcx> {
 145     /// The trait reference of the parent obligation that led to the
 146     /// current obligation. Note that only trait obligations lead to
 147     /// derived obligations, so we just store the trait reference here
 148     /// directly.
 149     parent_trait_ref: ty::PolyTraitRef<'tcx>,
 150
 151     /// The parent trait had this cause
 152     parent_code: Rc<ObligationCauseCode<'tcx>>
 153 }
 154
 155 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
 156 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
 157 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
 158
 159 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
 160
 161 #[derive(Clone,Debug)]
 162 pub enum SelectionError<'tcx> {
 163     Unimplemented,
 164     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
 165                                 ty::PolyTraitRef<'tcx>,
 166                                 ty::error::TypeError<'tcx>),
 167     TraitNotObjectSafe(DefId),
 168 }
 169
 170 pub struct FulfillmentError<'tcx> {
 171     pub obligation: PredicateObligation<'tcx>,
 172     pub code: FulfillmentErrorCode<'tcx>
 173 }
 174
 175 #[derive(Clone)]
 176 pub enum FulfillmentErrorCode<'tcx> {
 177     CodeSelectionError(SelectionError<'tcx>),
 178     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
 179     CodeAmbiguity,
 180 }
 181
 182 /// When performing resolution, it is typically the case that there
 183 /// can be one of three outcomes:
 184 ///
 185 /// - `Ok(Some(r))`: success occurred with result `r`
 186 /// - `Ok(None)`: could not definitely determine anything, usually due
 187 ///   to inconclusive type inference.
 188 /// - `Err(e)`: error `e` occurred
 189 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 190
 191 /// Given the successful resolution of an obligation, the `Vtable`
 192 /// indicates where the vtable comes from. Note that while we call this
 193 /// a "vtable", it does not necessarily indicate dynamic dispatch at
 194 /// runtime. `Vtable` instances just tell the compiler where to find
 195 /// methods, but in generic code those methods are typically statically
 196 /// dispatched -- only when an object is constructed is a `Vtable`
 197 /// instance reified into an actual vtable.
 198 ///
 199 /// For example, the vtable may be tied to a specific impl (case A),
 200 /// or it may be relative to some bound that is in scope (case B).
 201 ///
 202 ///
 203 /// ```
 204 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 205 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 206 /// impl Clone for int { ... }             // Impl_3
 207 ///
 208 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
 209 ///                 param: T,
 210 ///                 mixed: Option<T>) {
 211 ///
 212 ///    // Case A: Vtable points at a specific impl. Only possible when
 213 ///    // type is concretely known. If the impl itself has bounded
 214 ///    // type parameters, Vtable will carry resolutions for those as well:
 215 ///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 216 ///
 217 ///    // Case B: Vtable must be provided by caller. This applies when
 218 ///    // type is a type parameter.
 219 ///    param.clone();    // VtableParam
 220 ///
 221 ///    // Case C: A mix of cases A and B.
 222 ///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
 223 /// }
 224 /// ```
 225 ///
 226 /// ### The type parameter `N`
 227 ///
 228 /// See explanation on `VtableImplData`.
 229 #[derive(Clone)]
 230 pub enum Vtable<'tcx, N> {
 231     /// Vtable identifying a particular impl.
 232     VtableImpl(VtableImplData<'tcx, N>),
 233
 234     /// Vtable for default trait implementations
 235     /// This carries the information and nested obligations with regards
 236     /// to a default implementation for a trait `Trait`. The nested obligations
 237     /// ensure the trait implementation holds for all the constituent types.
 238     VtableDefaultImpl(VtableDefaultImplData<N>),
 239
 240     /// Successful resolution to an obligation provided by the caller
 241     /// for some type parameter. The `Vec<N>` represents the
 242     /// obligations incurred from normalizing the where-clause (if
 243     /// any).
 244     VtableParam(Vec<N>),
 245
 246     /// Virtual calls through an object
 247     VtableObject(VtableObjectData<'tcx, N>),
 248
 249     /// Successful resolution for a builtin trait.
 250     VtableBuiltin(VtableBuiltinData<N>),
 251
 252     /// Vtable automatically generated for a closure. The def ID is the ID
 253     /// of the closure expression. This is a `VtableImpl` in spirit, but the
 254     /// impl is generated by the compiler and does not appear in the source.
 255     VtableClosure(VtableClosureData<'tcx, N>),
 256
 257     /// Same as above, but for a fn pointer type with the given signature.
 258     VtableFnPointer(VtableFnPointerData<'tcx, N>),
 259 }
 260
 261 /// Identifies a particular impl in the source, along with a set of
 262 /// substitutions from the impl's type/lifetime parameters. The
 263 /// `nested` vector corresponds to the nested obligations attached to
 264 /// the impl's type parameters.
 265 ///
 266 /// The type parameter `N` indicates the type used for "nested
 267 /// obligations" that are required by the impl. During type check, this
 268 /// is `Obligation`, as one might expect. During trans, however, this
 269 /// is `()`, because trans only requires a shallow resolution of an
 270 /// impl, and nested obligations are satisfied later.
 271 #[derive(Clone, PartialEq, Eq)]
 272 pub struct VtableImplData<'tcx, N> {
 273     pub impl_def_id: DefId,
 274     pub substs: &'tcx subst::Substs<'tcx>,
 275     pub nested: Vec<N>
 276 }
 277
 278 #[derive(Clone, PartialEq, Eq)]
 279 pub struct VtableClosureData<'tcx, N> {
 280     pub closure_def_id: DefId,
 281     pub substs: ty::ClosureSubsts<'tcx>,
 282     /// Nested obligations. This can be non-empty if the closure
 283     /// signature contains associated types.
 284     pub nested: Vec<N>
 285 }
 286
 287 #[derive(Clone)]
 288 pub struct VtableDefaultImplData<N> {
 289     pub trait_def_id: DefId,
 290     pub nested: Vec<N>
 291 }
 292
 293 #[derive(Clone)]
 294 pub struct VtableBuiltinData<N> {
 295     pub nested: Vec<N>
 296 }
 297
 298 /// A vtable for some object-safe trait `Foo` automatically derived
 299 /// for the object type `Foo`.
 300 #[derive(PartialEq,Eq,Clone)]
 301 pub struct VtableObjectData<'tcx, N> {
 302     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 303     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 304
 305     /// The vtable is formed by concatenating together the method lists of
 306     /// the base object trait and all supertraits; this is the start of
 307     /// `upcast_trait_ref`'s methods in that vtable.
 308     pub vtable_base: usize,
 309
 310     pub nested: Vec<N>,
 311 }
 312
 313 #[derive(Clone, PartialEq, Eq)]
 314 pub struct VtableFnPointerData<'tcx, N> {
 315     pub fn_ty: ty::Ty<'tcx>,
 316     pub nested: Vec<N>
 317 }
 318
 319 /// Creates predicate obligations from the generic bounds.
 320 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 321                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 322                                      -> PredicateObligations<'tcx>
 323 {
 324     util::predicates_for_generics(cause, 0, generic_bounds)
 325 }
 326
 327 /// Determines whether the type `ty` is known to meet `bound` and
 328 /// returns true if so. Returns false if `ty` either does not meet
 329 /// `bound` or is not known to meet bound (note that this is
 330 /// conservative towards *no impl*, which is the opposite of the
 331 /// `evaluate` methods).
 332 pub fn type_known_to_meet_builtin_bound<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 333                                                         ty: Ty<'tcx>,
 334                                                         bound: ty::BuiltinBound,
 335                                                         span: Span)
 336                                                         -> bool
 337 {
 338     debug!("type_known_to_meet_builtin_bound(ty={:?}, bound={:?})",
 339            ty,
 340            bound);
 341
 342     let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 343     let obligation =
 344         infcx.tcx.predicate_for_builtin_bound(cause, bound, 0, ty);
 345     let obligation = match obligation {
 346         Ok(o) => o,
 347         Err(..) => return false
 348     };
 349     let result = SelectionContext::new(infcx)
 350         .evaluate_obligation_conservatively(&obligation);
 351     debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} => {:?}",
 352            ty, bound, result);
 353
 354     if result && (ty.has_infer_types() || ty.has_closure_types()) {
 355         // Because of inference "guessing", selection can sometimes claim
 356         // to succeed while the success requires a guess. To ensure
 357         // this function's result remains infallible, we must confirm
 358         // that guess. While imperfect, I believe this is sound.
 359
 360         let mut fulfill_cx = FulfillmentContext::new();
 361
 362         // We can use a dummy node-id here because we won't pay any mind
 363         // to region obligations that arise (there shouldn't really be any
 364         // anyhow).
 365         let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 366
 367         fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
 368
 369         // Note: we only assume something is `Copy` if we can
 370         // *definitively* show that it implements `Copy`. Otherwise,
 371         // assume it is move; linear is always ok.
 372         match fulfill_cx.select_all_or_error(infcx) {
 373             Ok(()) => {
 374                 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} success",
 375                        ty,
 376                        bound);
 377                 true
 378             }
 379             Err(e) => {
 380                 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} errors={:?}",
 381                        ty,
 382                        bound,
 383                        e);
 384                 false
 385             }
 386         }
 387     } else {
 388         result
 389     }
 390 }
 391
 392 // FIXME: this is gonna need to be removed ...
 393 /// Normalizes the parameter environment, reporting errors if they occur.
 394 pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 395     unnormalized_env: ty::ParameterEnvironment<'tcx>,
 396     cause: ObligationCause<'tcx>)
 397     -> ty::ParameterEnvironment<'tcx>
 398 {
 399     // I'm not wild about reporting errors here; I'd prefer to
 400     // have the errors get reported at a defined place (e.g.,
 401     // during typeck). Instead I have all parameter
 402     // environments, in effect, going through this function
 403     // and hence potentially reporting errors. This ensurse of
 404     // course that we never forget to normalize (the
 405     // alternative seemed like it would involve a lot of
 406     // manual invocations of this fn -- and then we'd have to
 407     // deal with the errors at each of those sites).
 408     //
 409     // In any case, in practice, typeck constructs all the
 410     // parameter environments once for every fn as it goes,
 411     // and errors will get reported then; so after typeck we
 412     // can be sure that no errors should occur.
 413
 414     let span = cause.span;
 415     let body_id = cause.body_id;
 416
 417     debug!("normalize_param_env_or_error(unnormalized_env={:?})",
 418            unnormalized_env);
 419
 420     let predicates: Vec<_> =
 421         util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.clone())
 422         .filter(|p| !p.is_global()) // (*)
 423         .collect();
 424
 425     // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
 426     // need to be in the *environment* to be proven, so screen those
 427     // out. This is important for the soundness of inter-fn
 428     // caching. Note though that we should probably check that these
 429     // predicates hold at the point where the environment is
 430     // constructed, but I am not currently doing so out of laziness.
 431     // -nmatsakis
 432
 433     debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
 434            predicates);
 435
 436     let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
 437
 438     tcx.infer_ctxt(None, Some(elaborated_env), ProjectionMode::AnyFinal).enter(|infcx| {
 439         let predicates = match fully_normalize(&infcx, cause,
 440                                                &infcx.parameter_environment.caller_bounds) {
 441             Ok(predicates) => predicates,
 442             Err(errors) => {
 443                 infcx.report_fulfillment_errors(&errors);
 444                 // An unnormalized env is better than nothing.
 445                 return infcx.parameter_environment;
 446             }
 447         };
 448
 449         debug!("normalize_param_env_or_error: normalized predicates={:?}",
 450             predicates);
 451
 452         let free_regions = FreeRegionMap::new();
 453         infcx.resolve_regions_and_report_errors(&free_regions, body_id);
 454         let predicates = match infcx.fully_resolve(&predicates) {
 455             Ok(predicates) => predicates,
 456             Err(fixup_err) => {
 457                 // If we encounter a fixup error, it means that some type
 458                 // variable wound up unconstrained. I actually don't know
 459                 // if this can happen, and I certainly don't expect it to
 460                 // happen often, but if it did happen it probably
 461                 // represents a legitimate failure due to some kind of
 462                 // unconstrained variable, and it seems better not to ICE,
 463                 // all things considered.
 464                 tcx.sess.span_err(span, &fixup_err.to_string());
 465                 // An unnormalized env is better than nothing.
 466                 return infcx.parameter_environment;
 467             }
 468         };
 469
 470         let predicates = match tcx.lift_to_global(&predicates) {
 471             Some(predicates) => predicates,
 472             None => return infcx.parameter_environment
 473         };
 474
 475         debug!("normalize_param_env_or_error: resolved predicates={:?}",
 476             predicates);
 477
 478         infcx.parameter_environment.with_caller_bounds(predicates)
 479     })
 480 }
 481
 482 pub fn fully_normalize<'a, 'gcx, 'tcx, T>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 483                                           cause: ObligationCause<'tcx>,
 484                                           value: &T)
 485                                           -> Result<T, Vec<FulfillmentError<'tcx>>>
 486     where T : TypeFoldable<'tcx>
 487 {
 488     debug!("fully_normalize(value={:?})", value);
 489
 490     let mut selcx = &mut SelectionContext::new(infcx);
 491     // FIXME (@jroesch) ISSUE 26721
 492     // I'm not sure if this is a bug or not, needs further investigation.
 493     // It appears that by reusing the fulfillment_cx here we incur more
 494     // obligations and later trip an asssertion on regionck.rs line 337.
 495     //
 496     // The two possibilities I see is:
 497     //      - normalization is not actually fully happening and we
 498     //        have a bug else where
 499     //      - we are adding a duplicate bound into the list causing
 500     //        its size to change.
 501     //
 502     // I think we should probably land this refactor and then come
 503     // back to this is a follow-up patch.
 504     let mut fulfill_cx = FulfillmentContext::new();
 505
 506     let Normalized { value: normalized_value, obligations } =
 507         project::normalize(selcx, cause, value);
 508     debug!("fully_normalize: normalized_value={:?} obligations={:?}",
 509            normalized_value,
 510            obligations);
 511     for obligation in obligations {
 512         fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
 513     }
 514
 515     debug!("fully_normalize: select_all_or_error start");
 516     match fulfill_cx.select_all_or_error(infcx) {
 517         Ok(()) => { }
 518         Err(e) => {
 519             debug!("fully_normalize: error={:?}", e);
 520             return Err(e);
 521         }
 522     }
 523     debug!("fully_normalize: select_all_or_error complete");
 524     let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
 525     debug!("fully_normalize: resolved_value={:?}", resolved_value);
 526     Ok(resolved_value)
 527 }
 528
 529 impl<'tcx,O> Obligation<'tcx,O> {
 530     pub fn new(cause: ObligationCause<'tcx>,
 531                trait_ref: O)
 532                -> Obligation<'tcx, O>
 533     {
 534         Obligation { cause: cause,
 535                      recursion_depth: 0,
 536                      predicate: trait_ref }
 537     }
 538
 539     fn with_depth(cause: ObligationCause<'tcx>,
 540                   recursion_depth: usize,
 541                   trait_ref: O)
 542                   -> Obligation<'tcx, O>
 543     {
 544         Obligation { cause: cause,
 545                      recursion_depth: recursion_depth,
 546                      predicate: trait_ref }
 547     }
 548
 549     pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
 550         Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
 551     }
 552
 553     pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
 554         Obligation { cause: self.cause.clone(),
 555                      recursion_depth: self.recursion_depth,
 556                      predicate: value }
 557     }
 558 }
 559
 560 impl<'tcx> ObligationCause<'tcx> {
 561     pub fn new(span: Span,
 562                body_id: ast::NodeId,
 563                code: ObligationCauseCode<'tcx>)
 564                -> ObligationCause<'tcx> {
 565         ObligationCause { span: span, body_id: body_id, code: code }
 566     }
 567
 568     pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
 569         ObligationCause { span: span, body_id: body_id, code: MiscObligation }
 570     }
 571
 572     pub fn dummy() -> ObligationCause<'tcx> {
 573         ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
 574     }
 575 }
 576
 577 impl<'tcx, N> Vtable<'tcx, N> {
 578     pub fn nested_obligations(self) -> Vec<N> {
 579         match self {
 580             VtableImpl(i) => i.nested,
 581             VtableParam(n) => n,
 582             VtableBuiltin(i) => i.nested,
 583             VtableDefaultImpl(d) => d.nested,
 584             VtableClosure(c) => c.nested,
 585             VtableObject(d) => d.nested,
 586             VtableFnPointer(d) => d.nested,
 587         }
 588     }
 589
 590     fn nested_obligations_mut(&mut self) -> &mut Vec<N> {
 591         match self {
 592             &mut VtableImpl(ref mut i) => &mut i.nested,
 593             &mut VtableParam(ref mut n) => n,
 594             &mut VtableBuiltin(ref mut i) => &mut i.nested,
 595             &mut VtableDefaultImpl(ref mut d) => &mut d.nested,
 596             &mut VtableClosure(ref mut c) => &mut c.nested,
 597             &mut VtableObject(ref mut d) => &mut d.nested,
 598             &mut VtableFnPointer(ref mut d) => &mut d.nested,
 599         }
 600     }
 601
 602     pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
 603         match self {
 604             VtableImpl(i) => VtableImpl(VtableImplData {
 605                 impl_def_id: i.impl_def_id,
 606                 substs: i.substs,
 607                 nested: i.nested.into_iter().map(f).collect(),
 608             }),
 609             VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
 610             VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
 611                 nested: i.nested.into_iter().map(f).collect(),
 612             }),
 613             VtableObject(o) => VtableObject(VtableObjectData {
 614                 upcast_trait_ref: o.upcast_trait_ref,
 615                 vtable_base: o.vtable_base,
 616                 nested: o.nested.into_iter().map(f).collect(),
 617             }),
 618             VtableDefaultImpl(d) => VtableDefaultImpl(VtableDefaultImplData {
 619                 trait_def_id: d.trait_def_id,
 620                 nested: d.nested.into_iter().map(f).collect(),
 621             }),
 622             VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
 623                 fn_ty: p.fn_ty,
 624                 nested: p.nested.into_iter().map(f).collect(),
 625             }),
 626             VtableClosure(c) => VtableClosure(VtableClosureData {
 627                 closure_def_id: c.closure_def_id,
 628                 substs: c.substs,
 629                 nested: c.nested.into_iter().map(f).collect(),
 630             })
 631         }
 632     }
 633 }
 634
 635 impl<'tcx> FulfillmentError<'tcx> {
 636     fn new(obligation: PredicateObligation<'tcx>,
 637            code: FulfillmentErrorCode<'tcx>)
 638            -> FulfillmentError<'tcx>
 639     {
 640         FulfillmentError { obligation: obligation, code: code }
 641     }
 642 }
 643
 644 impl<'tcx> TraitObligation<'tcx> {
 645     fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
 646         ty::Binder(self.predicate.skip_binder().self_ty())
 647     }
 648 }