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, 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, UserString};
  27
  28 pub use self::error_reporting::report_fulfillment_errors;
  29 pub use self::error_reporting::suggest_new_overflow_limit;
  30 pub use self::coherence::orphan_check;
  31 pub use self::coherence::OrphanCheckErr;
  32 pub use self::fulfill::{FulfillmentContext, RegionObligation};
  33 pub use self::project::MismatchedProjectionTypes;
  34 pub use self::project::normalize;
  35 pub use self::project::Normalized;
  36 pub use self::object_safety::is_object_safe;
  37 pub use self::object_safety::object_safety_violations;
  38 pub use self::object_safety::ObjectSafetyViolation;
  39 pub use self::object_safety::MethodViolationCode;
  40 pub use self::select::SelectionContext;
  41 pub use self::select::SelectionCache;
  42 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
  43 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
  44 pub use self::util::elaborate_predicates;
  45 pub use self::util::get_vtable_index_of_object_method;
  46 pub use self::util::trait_ref_for_builtin_bound;
  47 pub use self::util::supertraits;
  48 pub use self::util::Supertraits;
  49 pub use self::util::transitive_bounds;
  50 pub use self::util::upcast;
  51
  52 mod coherence;
  53 mod error_reporting;
  54 mod fulfill;
  55 mod project;
  56 mod object_safety;
  57 mod select;
  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: uint,
  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, 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, PartialEq, Eq)]
  93 pub enum ObligationCauseCode<'tcx> {
  94     /// Not well classified or should be obvious from span.
  95     MiscObligation,
  96
  97     /// In an impl of trait X for type Y, type Y must
  98     /// also implement all supertraits of X.
  99     ItemObligation(ast::DefId),
 100
 101     /// Obligation incurred due to an object cast.
 102     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 103
 104     /// Various cases where expressions must be sized/copy/etc:
 105     AssignmentLhsSized,        // L = X implies that L is Sized
 106     StructInitializerSized,    // S { ... } must be Sized
 107     VariableType(ast::NodeId), // Type of each variable must be Sized
 108     ReturnType,                // Return type must be Sized
 109     RepeatVec,                 // [T,..n] --> T must be Copy
 110
 111     // Captures of variable the given id by a closure (span is the
 112     // span of the closure)
 113     ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
 114
 115     // Types of fields (other than the last) in a struct must be sized.
 116     FieldSized,
 117
 118     // Only Sized types can be made into objects
 119     ObjectSized,
 120
 121     // static items must have `Sync` type
 122     SharedStatic,
 123
 124
 125     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 126
 127     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 128
 129     CompareImplMethodObligation,
 130 }
 131
 132 #[derive(Clone, PartialEq, Eq)]
 133 pub struct DerivedObligationCause<'tcx> {
 134     /// The trait reference of the parent obligation that led to the
 135     /// current obligation. Note that only trait obligations lead to
 136     /// derived obligations, so we just store the trait reference here
 137     /// directly.
 138     parent_trait_ref: ty::PolyTraitRef<'tcx>,
 139
 140     /// The parent trait had this cause
 141     parent_code: Rc<ObligationCauseCode<'tcx>>
 142 }
 143
 144 pub type Obligations<'tcx, O> = subst::VecPerParamSpace<Obligation<'tcx, O>>;
 145 pub type PredicateObligations<'tcx> = subst::VecPerParamSpace<PredicateObligation<'tcx>>;
 146 pub type TraitObligations<'tcx> = subst::VecPerParamSpace<TraitObligation<'tcx>>;
 147
 148 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
 149
 150 #[derive(Clone,Debug)]
 151 pub enum SelectionError<'tcx> {
 152     Unimplemented,
 153     Overflow,
 154     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
 155                                 ty::PolyTraitRef<'tcx>,
 156                                 ty::type_err<'tcx>),
 157 }
 158
 159 pub struct FulfillmentError<'tcx> {
 160     pub obligation: PredicateObligation<'tcx>,
 161     pub code: FulfillmentErrorCode<'tcx>
 162 }
 163
 164 #[derive(Clone)]
 165 pub enum FulfillmentErrorCode<'tcx> {
 166     CodeSelectionError(SelectionError<'tcx>),
 167     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
 168     CodeAmbiguity,
 169 }
 170
 171 /// When performing resolution, it is typically the case that there
 172 /// can be one of three outcomes:
 173 ///
 174 /// - `Ok(Some(r))`: success occurred with result `r`
 175 /// - `Ok(None)`: could not definitely determine anything, usually due
 176 ///   to inconclusive type inference.
 177 /// - `Err(e)`: error `e` occurred
 178 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 179
 180 /// Given the successful resolution of an obligation, the `Vtable`
 181 /// indicates where the vtable comes from. Note that while we call this
 182 /// a "vtable", it does not necessarily indicate dynamic dispatch at
 183 /// runtime. `Vtable` instances just tell the compiler where to find
 184 /// methods, but in generic code those methods are typically statically
 185 /// dispatched -- only when an object is constructed is a `Vtable`
 186 /// instance reified into an actual vtable.
 187 ///
 188 /// For example, the vtable may be tied to a specific impl (case A),
 189 /// or it may be relative to some bound that is in scope (case B).
 190 ///
 191 ///
 192 /// ```
 193 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 194 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 195 /// impl Clone for int { ... }             // Impl_3
 196 ///
 197 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
 198 ///                 param: T,
 199 ///                 mixed: Option<T>) {
 200 ///
 201 ///    // Case A: Vtable points at a specific impl. Only possible when
 202 ///    // type is concretely known. If the impl itself has bounded
 203 ///    // type parameters, Vtable will carry resolutions for those as well:
 204 ///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 205 ///
 206 ///    // Case B: Vtable must be provided by caller. This applies when
 207 ///    // type is a type parameter.
 208 ///    param.clone();    // VtableParam
 209 ///
 210 ///    // Case C: A mix of cases A and B.
 211 ///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
 212 /// }
 213 /// ```
 214 ///
 215 /// ### The type parameter `N`
 216 ///
 217 /// See explanation on `VtableImplData`.
 218 #[derive(Debug,Clone)]
 219 pub enum Vtable<'tcx, N> {
 220     /// Vtable identifying a particular impl.
 221     VtableImpl(VtableImplData<'tcx, N>),
 222
 223     /// Successful resolution to an obligation provided by the caller
 224     /// for some type parameter. The `Vec<N>` represents the
 225     /// obligations incurred from normalizing the where-clause (if
 226     /// any).
 227     VtableParam(Vec<N>),
 228
 229     /// Virtual calls through an object
 230     VtableObject(VtableObjectData<'tcx>),
 231
 232     /// Successful resolution for a builtin trait.
 233     VtableBuiltin(VtableBuiltinData<N>),
 234
 235     /// Vtable automatically generated for a closure. The def ID is the ID
 236     /// of the closure expression. This is a `VtableImpl` in spirit, but the
 237     /// impl is generated by the compiler and does not appear in the source.
 238     VtableClosure(ast::DefId, subst::Substs<'tcx>),
 239
 240     /// Same as above, but for a fn pointer type with the given signature.
 241     VtableFnPointer(ty::Ty<'tcx>),
 242 }
 243
 244 /// Identifies a particular impl in the source, along with a set of
 245 /// substitutions from the impl's type/lifetime parameters. The
 246 /// `nested` vector corresponds to the nested obligations attached to
 247 /// the impl's type parameters.
 248 ///
 249 /// The type parameter `N` indicates the type used for "nested
 250 /// obligations" that are required by the impl. During type check, this
 251 /// is `Obligation`, as one might expect. During trans, however, this
 252 /// is `()`, because trans only requires a shallow resolution of an
 253 /// impl, and nested obligations are satisfied later.
 254 #[derive(Clone, PartialEq, Eq)]
 255 pub struct VtableImplData<'tcx, N> {
 256     pub impl_def_id: ast::DefId,
 257     pub substs: subst::Substs<'tcx>,
 258     pub nested: subst::VecPerParamSpace<N>
 259 }
 260
 261 #[derive(Debug,Clone)]
 262 pub struct VtableBuiltinData<N> {
 263     pub nested: subst::VecPerParamSpace<N>
 264 }
 265
 266 /// A vtable for some object-safe trait `Foo` automatically derived
 267 /// for the object type `Foo`.
 268 #[derive(PartialEq,Eq,Clone)]
 269 pub struct VtableObjectData<'tcx> {
 270     pub object_ty: Ty<'tcx>,
 271 }
 272
 273 /// True if there exist types that satisfy both of the two given impls.
 274 pub fn overlapping_impls(infcx: &InferCtxt,
 275                          impl1_def_id: ast::DefId,
 276                          impl2_def_id: ast::DefId)
 277                          -> bool
 278 {
 279     coherence::impl_can_satisfy(infcx, impl1_def_id, impl2_def_id) &&
 280     coherence::impl_can_satisfy(infcx, impl2_def_id, impl1_def_id)
 281 }
 282
 283 /// Creates predicate obligations from the generic bounds.
 284 pub fn predicates_for_generics<'tcx>(tcx: &ty::ctxt<'tcx>,
 285                                      cause: ObligationCause<'tcx>,
 286                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 287                                      -> PredicateObligations<'tcx>
 288 {
 289     util::predicates_for_generics(tcx, cause, 0, generic_bounds)
 290 }
 291
 292 /// Determines whether the type `ty` is known to meet `bound` and
 293 /// returns true if so. Returns false if `ty` either does not meet
 294 /// `bound` or is not known to meet bound (note that this is
 295 /// conservative towards *no impl*, which is the opposite of the
 296 /// `evaluate` methods).
 297 pub fn evaluate_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
 298                                        typer: &ty::ClosureTyper<'tcx>,
 299                                        ty: Ty<'tcx>,
 300                                        bound: ty::BuiltinBound,
 301                                        span: Span)
 302                                        -> SelectionResult<'tcx, ()>
 303 {
 304     debug!("type_known_to_meet_builtin_bound(ty={}, bound={:?})",
 305            ty.repr(infcx.tcx),
 306            bound);
 307
 308     let mut fulfill_cx = FulfillmentContext::new();
 309
 310     // We can use a dummy node-id here because we won't pay any mind
 311     // to region obligations that arise (there shouldn't really be any
 312     // anyhow).
 313     let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 314
 315     fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
 316
 317     // Note: we only assume something is `Copy` if we can
 318     // *definitively* show that it implements `Copy`. Otherwise,
 319     // assume it is move; linear is always ok.
 320     let result = match fulfill_cx.select_all_or_error(infcx, typer) {
 321         Ok(()) => Ok(Some(())), // Success, we know it implements Copy.
 322         Err(errors) => {
 323             // Check if overflow occurred anywhere and propagate that.
 324             if errors.iter().any(
 325                 |err| match err.code { CodeSelectionError(Overflow) => true, _ => false })
 326             {
 327                 return Err(Overflow);
 328             }
 329
 330             // Otherwise, if there were any hard errors, propagate an
 331             // arbitrary one of those. If no hard errors at all,
 332             // report ambiguity.
 333             let sel_error =
 334                 errors.iter()
 335                       .filter_map(|err| {
 336                           match err.code {
 337                               CodeAmbiguity => None,
 338                               CodeSelectionError(ref e) => Some(e.clone()),
 339                               CodeProjectionError(_) => {
 340                                   infcx.tcx.sess.span_bug(
 341                                       span,
 342                                       "projection error while selecting?")
 343                               }
 344                           }
 345                       })
 346                       .next();
 347             match sel_error {
 348                 None => { Ok(None) }
 349                 Some(e) => { Err(e) }
 350             }
 351         }
 352     };
 353
 354     debug!("type_known_to_meet_builtin_bound: ty={} bound={:?} result={:?}",
 355            ty.repr(infcx.tcx),
 356            bound,
 357            result);
 358
 359     result
 360 }
 361
 362 pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
 363                                                  typer: &ty::ClosureTyper<'tcx>,
 364                                                  ty: Ty<'tcx>,
 365                                                  bound: ty::BuiltinBound,
 366                                                  span: Span)
 367                                                  -> bool
 368 {
 369     match evaluate_builtin_bound(infcx, typer, ty, bound, span) {
 370         Ok(Some(())) => {
 371             // definitely impl'd
 372             true
 373         }
 374         Ok(None) => {
 375             // ambiguous: if coherence check was successful, shouldn't
 376             // happen, but we might have reported an error and been
 377             // soldering on, so just treat this like not implemented
 378             false
 379         }
 380         Err(Overflow) => {
 381             span_err!(infcx.tcx.sess, span, E0285,
 382                 "overflow evaluating whether `{}` is `{}`",
 383                       ty.user_string(infcx.tcx),
 384                       bound.user_string(infcx.tcx));
 385             suggest_new_overflow_limit(infcx.tcx, span);
 386             false
 387         }
 388         Err(_) => {
 389             // other errors: not implemented.
 390             false
 391         }
 392     }
 393 }
 394
 395 pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
 396                                              cause: ObligationCause<'tcx>)
 397                                              -> ty::ParameterEnvironment<'a,'tcx>
 398 {
 399     match normalize_param_env(&unnormalized_env, cause) {
 400         Ok(p) => p,
 401         Err(errors) => {
 402             // I'm not wild about reporting errors here; I'd prefer to
 403             // have the errors get reported at a defined place (e.g.,
 404             // during typeck). Instead I have all parameter
 405             // environments, in effect, going through this function
 406             // and hence potentially reporting errors. This ensurse of
 407             // course that we never forget to normalize (the
 408             // alternative seemed like it would involve a lot of
 409             // manual invocations of this fn -- and then we'd have to
 410             // deal with the errors at each of those sites).
 411             //
 412             // In any case, in practice, typeck constructs all the
 413             // parameter environments once for every fn as it goes,
 414             // and errors will get reported then; so after typeck we
 415             // can be sure that no errors should occur.
 416             let infcx = infer::new_infer_ctxt(unnormalized_env.tcx);
 417             report_fulfillment_errors(&infcx, &errors);
 418
 419             // Normalized failed? use what they gave us, it's better than nothing.
 420             unnormalized_env
 421         }
 422     }
 423 }
 424
 425 pub fn normalize_param_env<'a,'tcx>(param_env: &ty::ParameterEnvironment<'a,'tcx>,
 426                                     cause: ObligationCause<'tcx>)
 427                                     -> Result<ty::ParameterEnvironment<'a,'tcx>,
 428                                               Vec<FulfillmentError<'tcx>>>
 429 {
 430     let tcx = param_env.tcx;
 431
 432     debug!("normalize_param_env(param_env={})",
 433            param_env.repr(tcx));
 434
 435     let infcx = infer::new_infer_ctxt(tcx);
 436     let predicates = try!(fully_normalize(&infcx, param_env, cause, &param_env.caller_bounds));
 437
 438     debug!("normalize_param_env: predicates={}",
 439            predicates.repr(tcx));
 440
 441     Ok(param_env.with_caller_bounds(predicates))
 442 }
 443
 444 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
 445                                   closure_typer: &ty::ClosureTyper<'tcx>,
 446                                   cause: ObligationCause<'tcx>,
 447                                   value: &T)
 448                                   -> Result<T, Vec<FulfillmentError<'tcx>>>
 449     where T : TypeFoldable<'tcx> + HasProjectionTypes + Clone + Repr<'tcx>
 450 {
 451     let tcx = closure_typer.tcx();
 452
 453     debug!("normalize_param_env(value={})",
 454            value.repr(tcx));
 455
 456     let mut selcx = &mut SelectionContext::new(infcx, closure_typer);
 457     let mut fulfill_cx = FulfillmentContext::new();
 458     let Normalized { value: normalized_value, obligations } =
 459         project::normalize(selcx, cause, value);
 460     debug!("normalize_param_env: normalized_value={} obligations={}",
 461            normalized_value.repr(tcx),
 462            obligations.repr(tcx));
 463     for obligation in obligations {
 464         fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
 465     }
 466     try!(fulfill_cx.select_all_or_error(infcx, closure_typer));
 467     let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
 468     debug!("normalize_param_env: resolved_value={}",
 469            resolved_value.repr(tcx));
 470     Ok(resolved_value)
 471 }
 472
 473 impl<'tcx,O> Obligation<'tcx,O> {
 474     pub fn new(cause: ObligationCause<'tcx>,
 475                trait_ref: O)
 476                -> Obligation<'tcx, O>
 477     {
 478         Obligation { cause: cause,
 479                      recursion_depth: 0,
 480                      predicate: trait_ref }
 481     }
 482
 483     fn with_depth(cause: ObligationCause<'tcx>,
 484                   recursion_depth: uint,
 485                   trait_ref: O)
 486                   -> Obligation<'tcx, O>
 487     {
 488         Obligation { cause: cause,
 489                      recursion_depth: recursion_depth,
 490                      predicate: trait_ref }
 491     }
 492
 493     pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
 494         Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
 495     }
 496
 497     pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
 498         Obligation { cause: self.cause.clone(),
 499                      recursion_depth: self.recursion_depth,
 500                      predicate: value }
 501     }
 502 }
 503
 504 impl<'tcx> ObligationCause<'tcx> {
 505     pub fn new(span: Span,
 506                body_id: ast::NodeId,
 507                code: ObligationCauseCode<'tcx>)
 508                -> ObligationCause<'tcx> {
 509         ObligationCause { span: span, body_id: body_id, code: code }
 510     }
 511
 512     pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
 513         ObligationCause { span: span, body_id: body_id, code: MiscObligation }
 514     }
 515
 516     pub fn dummy() -> ObligationCause<'tcx> {
 517         ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
 518     }
 519 }
 520
 521 impl<'tcx, N> Vtable<'tcx, N> {
 522     pub fn iter_nested(&self) -> Iter<N> {
 523         match *self {
 524             VtableImpl(ref i) => i.iter_nested(),
 525             VtableFnPointer(..) => (&[]).iter(),
 526             VtableClosure(..) => (&[]).iter(),
 527             VtableParam(ref n) => n.iter(),
 528             VtableObject(_) => (&[]).iter(),
 529             VtableBuiltin(ref i) => i.iter_nested(),
 530         }
 531     }
 532
 533     pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where F: FnMut(&N) -> M {
 534         match *self {
 535             VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
 536             VtableFnPointer(ref sig) => VtableFnPointer((*sig).clone()),
 537             VtableClosure(d, ref s) => VtableClosure(d, s.clone()),
 538             VtableParam(ref n) => VtableParam(n.iter().map(op).collect()),
 539             VtableObject(ref p) => VtableObject(p.clone()),
 540             VtableBuiltin(ref b) => VtableBuiltin(b.map_nested(op)),
 541         }
 542     }
 543
 544     pub fn map_move_nested<M, F>(self, op: F) -> Vtable<'tcx, M> where
 545         F: FnMut(N) -> M,
 546     {
 547         match self {
 548             VtableImpl(i) => VtableImpl(i.map_move_nested(op)),
 549             VtableFnPointer(sig) => VtableFnPointer(sig),
 550             VtableClosure(d, s) => VtableClosure(d, s),
 551             VtableParam(n) => VtableParam(n.into_iter().map(op).collect()),
 552             VtableObject(p) => VtableObject(p),
 553             VtableBuiltin(no) => VtableBuiltin(no.map_move_nested(op)),
 554         }
 555     }
 556 }
 557
 558 impl<'tcx, N> VtableImplData<'tcx, N> {
 559     pub fn iter_nested(&self) -> Iter<N> {
 560         self.nested.iter()
 561     }
 562
 563     pub fn map_nested<M, F>(&self, op: F) -> VtableImplData<'tcx, M> where
 564         F: FnMut(&N) -> M,
 565     {
 566         VtableImplData {
 567             impl_def_id: self.impl_def_id,
 568             substs: self.substs.clone(),
 569             nested: self.nested.map(op)
 570         }
 571     }
 572
 573     pub fn map_move_nested<M, F>(self, op: F) -> VtableImplData<'tcx, M> where
 574         F: FnMut(N) -> M,
 575     {
 576         let VtableImplData { impl_def_id, substs, nested } = self;
 577         VtableImplData {
 578             impl_def_id: impl_def_id,
 579             substs: substs,
 580             nested: nested.map_move(op)
 581         }
 582     }
 583 }
 584
 585 impl<N> VtableBuiltinData<N> {
 586     pub fn iter_nested(&self) -> Iter<N> {
 587         self.nested.iter()
 588     }
 589
 590     pub fn map_nested<M, F>(&self, op: F) -> VtableBuiltinData<M> where F: FnMut(&N) -> M {
 591         VtableBuiltinData {
 592             nested: self.nested.map(op)
 593         }
 594     }
 595
 596     pub fn map_move_nested<M, F>(self, op: F) -> VtableBuiltinData<M> where
 597         F: FnMut(N) -> M,
 598     {
 599         VtableBuiltinData {
 600             nested: self.nested.map_move(op)
 601         }
 602     }
 603 }
 604
 605 impl<'tcx> FulfillmentError<'tcx> {
 606     fn new(obligation: PredicateObligation<'tcx>,
 607            code: FulfillmentErrorCode<'tcx>)
 608            -> FulfillmentError<'tcx>
 609     {
 610         FulfillmentError { obligation: obligation, code: code }
 611     }
 612
 613     pub fn is_overflow(&self) -> bool {
 614         match self.code {
 615             CodeAmbiguity => false,
 616             CodeSelectionError(Overflow) => true,
 617             CodeSelectionError(_) => false,
 618             CodeProjectionError(_) => false,
 619         }
 620     }
 621 }
 622
 623 impl<'tcx> TraitObligation<'tcx> {
 624     fn self_ty(&self) -> Ty<'tcx> {
 625         self.predicate.0.self_ty()
 626     }
 627 }