src/librustc/middle/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 middle::subst;
  19 use middle::ty::{self, HasProjectionTypes, Ty};
  20 use middle::ty_fold::TypeFoldable;
  21 use middle::infer::{self, fixup_err_to_string, InferCtxt};
  22 use std::slice::Iter;
  23 use std::rc::Rc;
  24 use syntax::ast;
  25 use syntax::codemap::{Span, DUMMY_SP};
  26 use util::ppaux::Repr;
  27
  28 pub use self::error_reporting::report_fulfillment_errors;
  29 pub use self::error_reporting::report_overflow_error;
  30 pub use self::error_reporting::suggest_new_overflow_limit;
  31 pub use self::coherence::orphan_check;
  32 pub use self::coherence::overlapping_impls;
  33 pub use self::coherence::OrphanCheckErr;
  34 pub use self::fulfill::{FulfillmentContext, RegionObligation};
  35 pub use self::project::MismatchedProjectionTypes;
  36 pub use self::project::normalize;
  37 pub use self::project::Normalized;
  38 pub use self::object_safety::is_object_safe;
  39 pub use self::object_safety::object_safety_violations;
  40 pub use self::object_safety::ObjectSafetyViolation;
  41 pub use self::object_safety::MethodViolationCode;
  42 pub use self::object_safety::is_vtable_safe_method;
  43 pub use self::select::SelectionContext;
  44 pub use self::select::SelectionCache;
  45 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
  46 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
  47 pub use self::util::elaborate_predicates;
  48 pub use self::util::get_vtable_index_of_object_method;
  49 pub use self::util::trait_ref_for_builtin_bound;
  50 pub use self::util::supertraits;
  51 pub use self::util::Supertraits;
  52 pub use self::util::supertrait_def_ids;
  53 pub use self::util::SupertraitDefIds;
  54 pub use self::util::transitive_bounds;
  55 pub use self::util::upcast;
  56
  57 mod coherence;
  58 mod error_reporting;
  59 mod fulfill;
  60 mod project;
  61 mod object_safety;
  62 mod select;
  63 mod util;
  64
  65 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
  66 /// which the vtable must be found.  The process of finding a vtable is
  67 /// called "resolving" the `Obligation`. This process consists of
  68 /// either identifying an `impl` (e.g., `impl Eq for int`) that
  69 /// provides the required vtable, or else finding a bound that is in
  70 /// scope. The eventual result is usually a `Selection` (defined below).
  71 #[derive(Clone, PartialEq, Eq)]
  72 pub struct Obligation<'tcx, T> {
  73     pub cause: ObligationCause<'tcx>,
  74     pub recursion_depth: usize,
  75     pub predicate: T,
  76 }
  77
  78 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
  79 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
  80
  81 /// Why did we incur this obligation? Used for error reporting.
  82 #[derive(Clone, PartialEq, Eq)]
  83 pub struct ObligationCause<'tcx> {
  84     pub span: Span,
  85
  86     // The id of the fn body that triggered this obligation. This is
  87     // used for region obligations to determine the precise
  88     // environment in which the region obligation should be evaluated
  89     // (in particular, closures can add new assumptions). See the
  90     // field `region_obligations` of the `FulfillmentContext` for more
  91     // information.
  92     pub body_id: ast::NodeId,
  93
  94     pub code: ObligationCauseCode<'tcx>
  95 }
  96
  97 #[derive(Clone, PartialEq, Eq)]
  98 pub enum ObligationCauseCode<'tcx> {
  99     /// Not well classified or should be obvious from span.
 100     MiscObligation,
 101
 102     /// In an impl of trait X for type Y, type Y must
 103     /// also implement all supertraits of X.
 104     ItemObligation(ast::DefId),
 105
 106     /// Obligation incurred due to an object cast.
 107     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 108
 109     /// Various cases where expressions must be sized/copy/etc:
 110     AssignmentLhsSized,        // L = X implies that L is Sized
 111     StructInitializerSized,    // S { ... } must be Sized
 112     VariableType(ast::NodeId), // Type of each variable must be Sized
 113     ReturnType,                // Return type must be Sized
 114     RepeatVec,                 // [T,..n] --> T must be Copy
 115
 116     // Captures of variable the given id by a closure (span is the
 117     // span of the closure)
 118     ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
 119
 120     // Types of fields (other than the last) in a struct must be sized.
 121     FieldSized,
 122
 123     // Only Sized types can be made into objects
 124     ObjectSized,
 125
 126     // static items must have `Sync` type
 127     SharedStatic,
 128
 129
 130     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 131
 132     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 133
 134     CompareImplMethodObligation,
 135 }
 136
 137 #[derive(Clone, PartialEq, Eq)]
 138 pub struct DerivedObligationCause<'tcx> {
 139     /// The trait reference of the parent obligation that led to the
 140     /// current obligation. Note that only trait obligations lead to
 141     /// derived obligations, so we just store the trait reference here
 142     /// directly.
 143     parent_trait_ref: ty::PolyTraitRef<'tcx>,
 144
 145     /// The parent trait had this cause
 146     parent_code: Rc<ObligationCauseCode<'tcx>>
 147 }
 148
 149 pub type Obligations<'tcx, O> = subst::VecPerParamSpace<Obligation<'tcx, O>>;
 150 pub type PredicateObligations<'tcx> = subst::VecPerParamSpace<PredicateObligation<'tcx>>;
 151 pub type TraitObligations<'tcx> = subst::VecPerParamSpace<TraitObligation<'tcx>>;
 152
 153 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
 154
 155 #[derive(Clone,Debug)]
 156 pub enum SelectionError<'tcx> {
 157     Unimplemented,
 158     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
 159                                 ty::PolyTraitRef<'tcx>,
 160                                 ty::type_err<'tcx>),
 161 }
 162
 163 pub struct FulfillmentError<'tcx> {
 164     pub obligation: PredicateObligation<'tcx>,
 165     pub code: FulfillmentErrorCode<'tcx>
 166 }
 167
 168 #[derive(Clone)]
 169 pub enum FulfillmentErrorCode<'tcx> {
 170     CodeSelectionError(SelectionError<'tcx>),
 171     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
 172     CodeAmbiguity,
 173 }
 174
 175 /// When performing resolution, it is typically the case that there
 176 /// can be one of three outcomes:
 177 ///
 178 /// - `Ok(Some(r))`: success occurred with result `r`
 179 /// - `Ok(None)`: could not definitely determine anything, usually due
 180 ///   to inconclusive type inference.
 181 /// - `Err(e)`: error `e` occurred
 182 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 183
 184 /// Given the successful resolution of an obligation, the `Vtable`
 185 /// indicates where the vtable comes from. Note that while we call this
 186 /// a "vtable", it does not necessarily indicate dynamic dispatch at
 187 /// runtime. `Vtable` instances just tell the compiler where to find
 188 /// methods, but in generic code those methods are typically statically
 189 /// dispatched -- only when an object is constructed is a `Vtable`
 190 /// instance reified into an actual vtable.
 191 ///
 192 /// For example, the vtable may be tied to a specific impl (case A),
 193 /// or it may be relative to some bound that is in scope (case B).
 194 ///
 195 ///
 196 /// ```
 197 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 198 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 199 /// impl Clone for int { ... }             // Impl_3
 200 ///
 201 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
 202 ///                 param: T,
 203 ///                 mixed: Option<T>) {
 204 ///
 205 ///    // Case A: Vtable points at a specific impl. Only possible when
 206 ///    // type is concretely known. If the impl itself has bounded
 207 ///    // type parameters, Vtable will carry resolutions for those as well:
 208 ///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 209 ///
 210 ///    // Case B: Vtable must be provided by caller. This applies when
 211 ///    // type is a type parameter.
 212 ///    param.clone();    // VtableParam
 213 ///
 214 ///    // Case C: A mix of cases A and B.
 215 ///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
 216 /// }
 217 /// ```
 218 ///
 219 /// ### The type parameter `N`
 220 ///
 221 /// See explanation on `VtableImplData`.
 222 #[derive(Debug,Clone)]
 223 pub enum Vtable<'tcx, N> {
 224     /// Vtable identifying a particular impl.
 225     VtableImpl(VtableImplData<'tcx, N>),
 226
 227     /// Vtable for default trait implementations
 228     /// This carries the information and nested obligations with regards
 229     /// to a default implementation for a trait `Trait`. The nested obligations
 230     /// ensure the trait implementation holds for all the constituent types.
 231     VtableDefaultImpl(VtableDefaultImplData<N>),
 232
 233     /// Successful resolution to an obligation provided by the caller
 234     /// for some type parameter. The `Vec<N>` represents the
 235     /// obligations incurred from normalizing the where-clause (if
 236     /// any).
 237     VtableParam(Vec<N>),
 238
 239     /// Virtual calls through an object
 240     VtableObject(VtableObjectData<'tcx>),
 241
 242     /// Successful resolution for a builtin trait.
 243     VtableBuiltin(VtableBuiltinData<N>),
 244
 245     /// Vtable automatically generated for a closure. The def ID is the ID
 246     /// of the closure expression. This is a `VtableImpl` in spirit, but the
 247     /// impl is generated by the compiler and does not appear in the source.
 248     VtableClosure(ast::DefId, subst::Substs<'tcx>),
 249
 250     /// Same as above, but for a fn pointer type with the given signature.
 251     VtableFnPointer(ty::Ty<'tcx>),
 252 }
 253
 254 /// Identifies a particular impl in the source, along with a set of
 255 /// substitutions from the impl's type/lifetime parameters. The
 256 /// `nested` vector corresponds to the nested obligations attached to
 257 /// the impl's type parameters.
 258 ///
 259 /// The type parameter `N` indicates the type used for "nested
 260 /// obligations" that are required by the impl. During type check, this
 261 /// is `Obligation`, as one might expect. During trans, however, this
 262 /// is `()`, because trans only requires a shallow resolution of an
 263 /// impl, and nested obligations are satisfied later.
 264 #[derive(Clone, PartialEq, Eq)]
 265 pub struct VtableImplData<'tcx, N> {
 266     pub impl_def_id: ast::DefId,
 267     pub substs: subst::Substs<'tcx>,
 268     pub nested: subst::VecPerParamSpace<N>
 269 }
 270
 271 #[derive(Debug,Clone)]
 272 pub struct VtableDefaultImplData<N> {
 273     pub trait_def_id: ast::DefId,
 274     pub nested: Vec<N>
 275 }
 276
 277 #[derive(Debug,Clone)]
 278 pub struct VtableBuiltinData<N> {
 279     pub nested: subst::VecPerParamSpace<N>
 280 }
 281
 282 /// A vtable for some object-safe trait `Foo` automatically derived
 283 /// for the object type `Foo`.
 284 #[derive(PartialEq,Eq,Clone)]
 285 pub struct VtableObjectData<'tcx> {
 286     /// the object type `Foo`.
 287     pub object_ty: Ty<'tcx>,
 288
 289     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 290     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 291 }
 292
 293 /// Creates predicate obligations from the generic bounds.
 294 pub fn predicates_for_generics<'tcx>(tcx: &ty::ctxt<'tcx>,
 295                                      cause: ObligationCause<'tcx>,
 296                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 297                                      -> PredicateObligations<'tcx>
 298 {
 299     util::predicates_for_generics(tcx, cause, 0, generic_bounds)
 300 }
 301
 302 /// Determines whether the type `ty` is known to meet `bound` and
 303 /// returns true if so. Returns false if `ty` either does not meet
 304 /// `bound` or is not known to meet bound (note that this is
 305 /// conservative towards *no impl*, which is the opposite of the
 306 /// `evaluate` methods).
 307 pub fn evaluate_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
 308                                        typer: &ty::ClosureTyper<'tcx>,
 309                                        ty: Ty<'tcx>,
 310                                        bound: ty::BuiltinBound,
 311                                        span: Span)
 312                                        -> SelectionResult<'tcx, ()>
 313 {
 314     debug!("type_known_to_meet_builtin_bound(ty={}, bound={:?})",
 315            ty.repr(infcx.tcx),
 316            bound);
 317
 318     let mut fulfill_cx = FulfillmentContext::new();
 319
 320     // We can use a dummy node-id here because we won't pay any mind
 321     // to region obligations that arise (there shouldn't really be any
 322     // anyhow).
 323     let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 324
 325     fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
 326
 327     // Note: we only assume something is `Copy` if we can
 328     // *definitively* show that it implements `Copy`. Otherwise,
 329     // assume it is move; linear is always ok.
 330     let result = match fulfill_cx.select_all_or_error(infcx, typer) {
 331         Ok(()) => Ok(Some(())), // Success, we know it implements Copy.
 332         Err(errors) => {
 333             // If there were any hard errors, propagate an arbitrary
 334             // one of those. If no hard errors at all, report
 335             // ambiguity.
 336             let sel_error =
 337                 errors.iter()
 338                       .filter_map(|err| {
 339                           match err.code {
 340                               CodeAmbiguity => None,
 341                               CodeSelectionError(ref e) => Some(e.clone()),
 342                               CodeProjectionError(_) => {
 343                                   infcx.tcx.sess.span_bug(
 344                                       span,
 345                                       "projection error while selecting?")
 346                               }
 347                           }
 348                       })
 349                       .next();
 350             match sel_error {
 351                 None => { Ok(None) }
 352                 Some(e) => { Err(e) }
 353             }
 354         }
 355     };
 356
 357     debug!("type_known_to_meet_builtin_bound: ty={} bound={:?} result={:?}",
 358            ty.repr(infcx.tcx),
 359            bound,
 360            result);
 361
 362     result
 363 }
 364
 365 pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
 366                                                  typer: &ty::ClosureTyper<'tcx>,
 367                                                  ty: Ty<'tcx>,
 368                                                  bound: ty::BuiltinBound,
 369                                                  span: Span)
 370                                                  -> bool
 371 {
 372     match evaluate_builtin_bound(infcx, typer, ty, bound, span) {
 373         Ok(Some(())) => {
 374             // definitely impl'd
 375             true
 376         }
 377         Ok(None) => {
 378             // ambiguous: if coherence check was successful, shouldn't
 379             // happen, but we might have reported an error and been
 380             // soldering on, so just treat this like not implemented
 381             false
 382         }
 383         Err(_) => {
 384             // errors: not implemented.
 385             false
 386         }
 387     }
 388 }
 389
 390 /// Normalizes the parameter environment, reporting errors if they occur.
 391 pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
 392                                              cause: ObligationCause<'tcx>)
 393                                              -> ty::ParameterEnvironment<'a,'tcx>
 394 {
 395     // I'm not wild about reporting errors here; I'd prefer to
 396     // have the errors get reported at a defined place (e.g.,
 397     // during typeck). Instead I have all parameter
 398     // environments, in effect, going through this function
 399     // and hence potentially reporting errors. This ensurse of
 400     // course that we never forget to normalize (the
 401     // alternative seemed like it would involve a lot of
 402     // manual invocations of this fn -- and then we'd have to
 403     // deal with the errors at each of those sites).
 404     //
 405     // In any case, in practice, typeck constructs all the
 406     // parameter environments once for every fn as it goes,
 407     // and errors will get reported then; so after typeck we
 408     // can be sure that no errors should occur.
 409
 410     let tcx = unnormalized_env.tcx;
 411     let span = cause.span;
 412     let body_id = cause.body_id;
 413
 414     debug!("normalize_param_env_or_error(unnormalized_env={})",
 415            unnormalized_env.repr(tcx));
 416
 417     let infcx = infer::new_infer_ctxt(tcx);
 418     let predicates = match fully_normalize(&infcx, &unnormalized_env, cause,
 419                                            &unnormalized_env.caller_bounds) {
 420         Ok(predicates) => predicates,
 421         Err(errors) => {
 422             report_fulfillment_errors(&infcx, &errors);
 423             return unnormalized_env; // an unnormalized env is better than nothing
 424         }
 425     };
 426
 427     infcx.resolve_regions_and_report_errors(body_id);
 428     let predicates = match infcx.fully_resolve(&predicates) {
 429         Ok(predicates) => predicates,
 430         Err(fixup_err) => {
 431             // If we encounter a fixup error, it means that some type
 432             // variable wound up unconstrained. I actually don't know
 433             // if this can happen, and I certainly don't expect it to
 434             // happen often, but if it did happen it probably
 435             // represents a legitimate failure due to some kind of
 436             // unconstrained variable, and it seems better not to ICE,
 437             // all things considered.
 438             let err_msg = fixup_err_to_string(fixup_err);
 439             tcx.sess.span_err(span, &err_msg);
 440             return unnormalized_env; // an unnormalized env is better than nothing
 441         }
 442     };
 443
 444     debug!("normalize_param_env_or_error: predicates={}",
 445            predicates.repr(tcx));
 446
 447     unnormalized_env.with_caller_bounds(predicates)
 448 }
 449
 450 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
 451                                   closure_typer: &ty::ClosureTyper<'tcx>,
 452                                   cause: ObligationCause<'tcx>,
 453                                   value: &T)
 454                                   -> Result<T, Vec<FulfillmentError<'tcx>>>
 455     where T : TypeFoldable<'tcx> + HasProjectionTypes + Clone + Repr<'tcx>
 456 {
 457     let tcx = closure_typer.tcx();
 458
 459     debug!("normalize_param_env(value={})", value.repr(tcx));
 460
 461     let mut selcx = &mut SelectionContext::new(infcx, closure_typer);
 462     let mut fulfill_cx = FulfillmentContext::new();
 463     let Normalized { value: normalized_value, obligations } =
 464         project::normalize(selcx, cause, value);
 465     debug!("normalize_param_env: normalized_value={} obligations={}",
 466            normalized_value.repr(tcx),
 467            obligations.repr(tcx));
 468     for obligation in obligations {
 469         fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
 470     }
 471     try!(fulfill_cx.select_all_or_error(infcx, closure_typer));
 472     let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
 473     debug!("normalize_param_env: resolved_value={}", resolved_value.repr(tcx));
 474     Ok(resolved_value)
 475 }
 476
 477 impl<'tcx,O> Obligation<'tcx,O> {
 478     pub fn new(cause: ObligationCause<'tcx>,
 479                trait_ref: O)
 480                -> Obligation<'tcx, O>
 481     {
 482         Obligation { cause: cause,
 483                      recursion_depth: 0,
 484                      predicate: trait_ref }
 485     }
 486
 487     fn with_depth(cause: ObligationCause<'tcx>,
 488                   recursion_depth: usize,
 489                   trait_ref: O)
 490                   -> Obligation<'tcx, O>
 491     {
 492         Obligation { cause: cause,
 493                      recursion_depth: recursion_depth,
 494                      predicate: trait_ref }
 495     }
 496
 497     pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
 498         Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
 499     }
 500
 501     pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
 502         Obligation { cause: self.cause.clone(),
 503                      recursion_depth: self.recursion_depth,
 504                      predicate: value }
 505     }
 506 }
 507
 508 impl<'tcx> ObligationCause<'tcx> {
 509     pub fn new(span: Span,
 510                body_id: ast::NodeId,
 511                code: ObligationCauseCode<'tcx>)
 512                -> ObligationCause<'tcx> {
 513         ObligationCause { span: span, body_id: body_id, code: code }
 514     }
 515
 516     pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
 517         ObligationCause { span: span, body_id: body_id, code: MiscObligation }
 518     }
 519
 520     pub fn dummy() -> ObligationCause<'tcx> {
 521         ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
 522     }
 523 }
 524
 525 impl<'tcx, N> Vtable<'tcx, N> {
 526     pub fn iter_nested(&self) -> Iter<N> {
 527         match *self {
 528             VtableImpl(ref i) => i.iter_nested(),
 529             VtableParam(ref n) => n.iter(),
 530             VtableBuiltin(ref i) => i.iter_nested(),
 531             VtableObject(_) |
 532             VtableDefaultImpl(..) | VtableFnPointer(..) |
 533             VtableClosure(..) => (&[]).iter(),
 534         }
 535     }
 536
 537     pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where F: FnMut(&N) -> M {
 538         match *self {
 539             VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
 540             VtableDefaultImpl(ref t) => VtableDefaultImpl(t.map_nested(op)),
 541             VtableFnPointer(ref sig) => VtableFnPointer((*sig).clone()),
 542             VtableClosure(d, ref s) => VtableClosure(d, s.clone()),
 543             VtableParam(ref n) => VtableParam(n.iter().map(op).collect()),
 544             VtableObject(ref p) => VtableObject(p.clone()),
 545             VtableBuiltin(ref b) => VtableBuiltin(b.map_nested(op)),
 546         }
 547     }
 548
 549     pub fn map_move_nested<M, F>(self, op: F) -> Vtable<'tcx, M> where
 550         F: FnMut(N) -> M,
 551     {
 552         match self {
 553             VtableImpl(i) => VtableImpl(i.map_move_nested(op)),
 554             VtableFnPointer(sig) => VtableFnPointer(sig),
 555             VtableClosure(d, s) => VtableClosure(d, s),
 556             VtableDefaultImpl(t) => VtableDefaultImpl(t.map_move_nested(op)),
 557             VtableParam(n) => VtableParam(n.into_iter().map(op).collect()),
 558             VtableObject(p) => VtableObject(p),
 559             VtableBuiltin(no) => VtableBuiltin(no.map_move_nested(op)),
 560         }
 561     }
 562 }
 563
 564 impl<'tcx, N> VtableImplData<'tcx, N> {
 565     pub fn iter_nested(&self) -> Iter<N> {
 566         self.nested.iter()
 567     }
 568
 569     pub fn map_nested<M, F>(&self, op: F) -> VtableImplData<'tcx, M> where
 570         F: FnMut(&N) -> M,
 571     {
 572         VtableImplData {
 573             impl_def_id: self.impl_def_id,
 574             substs: self.substs.clone(),
 575             nested: self.nested.map(op)
 576         }
 577     }
 578
 579     pub fn map_move_nested<M, F>(self, op: F) -> VtableImplData<'tcx, M> where
 580         F: FnMut(N) -> M,
 581     {
 582         let VtableImplData { impl_def_id, substs, nested } = self;
 583         VtableImplData {
 584             impl_def_id: impl_def_id,
 585             substs: substs,
 586             nested: nested.map_move(op)
 587         }
 588     }
 589 }
 590
 591 impl<N> VtableDefaultImplData<N> {
 592     pub fn iter_nested(&self) -> Iter<N> {
 593         self.nested.iter()
 594     }
 595
 596     pub fn map_nested<M, F>(&self, op: F) -> VtableDefaultImplData<M> where
 597         F: FnMut(&N) -> M,
 598     {
 599         VtableDefaultImplData {
 600             trait_def_id: self.trait_def_id,
 601             nested: self.nested.iter().map(op).collect()
 602         }
 603     }
 604
 605     pub fn map_move_nested<M, F>(self, op: F) -> VtableDefaultImplData<M> where
 606         F: FnMut(N) -> M,
 607     {
 608         let VtableDefaultImplData { trait_def_id, nested } = self;
 609         VtableDefaultImplData {
 610             trait_def_id: trait_def_id,
 611             nested: nested.into_iter().map(op).collect()
 612         }
 613     }
 614 }
 615
 616 impl<N> VtableBuiltinData<N> {
 617     pub fn iter_nested(&self) -> Iter<N> {
 618         self.nested.iter()
 619     }
 620
 621     pub fn map_nested<M, F>(&self, op: F) -> VtableBuiltinData<M> where F: FnMut(&N) -> M {
 622         VtableBuiltinData {
 623             nested: self.nested.map(op)
 624         }
 625     }
 626
 627     pub fn map_move_nested<M, F>(self, op: F) -> VtableBuiltinData<M> where
 628         F: FnMut(N) -> M,
 629     {
 630         VtableBuiltinData {
 631             nested: self.nested.map_move(op)
 632         }
 633     }
 634 }
 635
 636 impl<'tcx> FulfillmentError<'tcx> {
 637     fn new(obligation: PredicateObligation<'tcx>,
 638            code: FulfillmentErrorCode<'tcx>)
 639            -> FulfillmentError<'tcx>
 640     {
 641         FulfillmentError { obligation: obligation, code: code }
 642     }
 643 }
 644
 645 impl<'tcx> TraitObligation<'tcx> {
 646     fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
 647         ty::Binder(self.predicate.skip_binder().self_ty())
 648     }
 649 }