compiler/rustc_middle/src/traits/mod.rs

   1 //! Trait Resolution. See the [rustc dev guide] for more information on how this works.
   2 //!
   3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
   4
   5 mod chalk;
   6 pub mod query;
   7 pub mod select;
   8 pub mod specialization_graph;
   9 mod structural_impls;
  10
  11 use crate::infer::canonical::Canonical;
  12 use crate::mir::interpret::ErrorHandled;
  13 use crate::ty::subst::SubstsRef;
  14 use crate::ty::{self, AdtKind, Ty, TyCtxt};
  15
  16 use rustc_errors::{Applicability, DiagnosticBuilder};
  17 use rustc_hir as hir;
  18 use rustc_hir::def_id::DefId;
  19 use rustc_span::symbol::Symbol;
  20 use rustc_span::{Span, DUMMY_SP};
  21 use smallvec::SmallVec;
  22
  23 use std::borrow::Cow;
  24 use std::fmt;
  25 use std::ops::Deref;
  26 use std::rc::Rc;
  27
  28 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
  29
  30 pub type CanonicalChalkEnvironmentAndGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>;
  31
  32 pub use self::ObligationCauseCode::*;
  33
  34 pub use self::chalk::{ChalkEnvironmentAndGoal, RustInterner as ChalkRustInterner};
  35
  36 /// Depending on the stage of compilation, we want projection to be
  37 /// more or less conservative.
  38 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
  39 pub enum Reveal {
  40     /// At type-checking time, we refuse to project any associated
  41     /// type that is marked `default`. Non-`default` ("final") types
  42     /// are always projected. This is necessary in general for
  43     /// soundness of specialization. However, we *could* allow
  44     /// projections in fully-monomorphic cases. We choose not to,
  45     /// because we prefer for `default type` to force the type
  46     /// definition to be treated abstractly by any consumers of the
  47     /// impl. Concretely, that means that the following example will
  48     /// fail to compile:
  49     ///
  50     /// ```
  51     /// trait Assoc {
  52     ///     type Output;
  53     /// }
  54     ///
  55     /// impl<T> Assoc for T {
  56     ///     default type Output = bool;
  57     /// }
  58     ///
  59     /// fn main() {
  60     ///     let <() as Assoc>::Output = true;
  61     /// }
  62     /// ```
  63     UserFacing,
  64
  65     /// At codegen time, all monomorphic projections will succeed.
  66     /// Also, `impl Trait` is normalized to the concrete type,
  67     /// which has to be already collected by type-checking.
  68     ///
  69     /// NOTE: as `impl Trait`'s concrete type should *never*
  70     /// be observable directly by the user, `Reveal::All`
  71     /// should not be used by checks which may expose
  72     /// type equality or type contents to the user.
  73     /// There are some exceptions, e.g., around OIBITS and
  74     /// transmute-checking, which expose some details, but
  75     /// not the whole concrete type of the `impl Trait`.
  76     All,
  77 }
  78
  79 /// The reason why we incurred this obligation; used for error reporting.
  80 ///
  81 /// As the happy path does not care about this struct, storing this on the heap
  82 /// ends up increasing performance.
  83 ///
  84 /// We do not want to intern this as there are a lot of obligation causes which
  85 /// only live for a short period of time.
  86 #[derive(Clone, PartialEq, Eq, Hash, Lift)]
  87 pub struct ObligationCause<'tcx> {
  88     /// `None` for `ObligationCause::dummy`, `Some` otherwise.
  89     data: Option<Rc<ObligationCauseData<'tcx>>>,
  90 }
  91
  92 const DUMMY_OBLIGATION_CAUSE_DATA: ObligationCauseData<'static> =
  93     ObligationCauseData { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation };
  94
  95 // Correctly format `ObligationCause::dummy`.
  96 impl<'tcx> fmt::Debug for ObligationCause<'tcx> {
  97     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  98         ObligationCauseData::fmt(self, f)
  99     }
 100 }
 101
 102 impl Deref for ObligationCause<'tcx> {
 103     type Target = ObligationCauseData<'tcx>;
 104
 105     #[inline(always)]
 106     fn deref(&self) -> &Self::Target {
 107         self.data.as_deref().unwrap_or(&DUMMY_OBLIGATION_CAUSE_DATA)
 108     }
 109 }
 110
 111 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 112 pub struct ObligationCauseData<'tcx> {
 113     pub span: Span,
 114
 115     /// The ID of the fn body that triggered this obligation. This is
 116     /// used for region obligations to determine the precise
 117     /// environment in which the region obligation should be evaluated
 118     /// (in particular, closures can add new assumptions). See the
 119     /// field `region_obligations` of the `FulfillmentContext` for more
 120     /// information.
 121     pub body_id: hir::HirId,
 122
 123     pub code: ObligationCauseCode<'tcx>,
 124 }
 125
 126 impl<'tcx> ObligationCause<'tcx> {
 127     #[inline]
 128     pub fn new(
 129         span: Span,
 130         body_id: hir::HirId,
 131         code: ObligationCauseCode<'tcx>,
 132     ) -> ObligationCause<'tcx> {
 133         ObligationCause { data: Some(Rc::new(ObligationCauseData { span, body_id, code })) }
 134     }
 135
 136     pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
 137         ObligationCause::new(span, body_id, MiscObligation)
 138     }
 139
 140     pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
 141         ObligationCause::new(span, hir::CRATE_HIR_ID, MiscObligation)
 142     }
 143
 144     #[inline(always)]
 145     pub fn dummy() -> ObligationCause<'tcx> {
 146         ObligationCause { data: None }
 147     }
 148
 149     pub fn make_mut(&mut self) -> &mut ObligationCauseData<'tcx> {
 150         Rc::make_mut(self.data.get_or_insert_with(|| Rc::new(DUMMY_OBLIGATION_CAUSE_DATA)))
 151     }
 152
 153     pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
 154         match self.code {
 155             ObligationCauseCode::CompareImplMethodObligation { .. }
 156             | ObligationCauseCode::MainFunctionType
 157             | ObligationCauseCode::StartFunctionType => {
 158                 tcx.sess.source_map().guess_head_span(self.span)
 159             }
 160             ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
 161                 arm_span,
 162                 ..
 163             }) => arm_span,
 164             _ => self.span,
 165         }
 166     }
 167 }
 168
 169 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 170 pub struct UnifyReceiverContext<'tcx> {
 171     pub assoc_item: ty::AssocItem,
 172     pub param_env: ty::ParamEnv<'tcx>,
 173     pub substs: SubstsRef<'tcx>,
 174 }
 175
 176 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 177 pub enum ObligationCauseCode<'tcx> {
 178     /// Not well classified or should be obvious from the span.
 179     MiscObligation,
 180
 181     /// A slice or array is WF only if `T: Sized`.
 182     SliceOrArrayElem,
 183
 184     /// A tuple is WF only if its middle elements are `Sized`.
 185     TupleElem,
 186
 187     /// This is the trait reference from the given projection.
 188     ProjectionWf(ty::ProjectionTy<'tcx>),
 189
 190     /// In an impl of trait `X` for type `Y`, type `Y` must
 191     /// also implement all supertraits of `X`.
 192     ItemObligation(DefId),
 193
 194     /// Like `ItemObligation`, but with extra detail on the source of the obligation.
 195     BindingObligation(DefId, Span),
 196
 197     /// A type like `&'a T` is WF only if `T: 'a`.
 198     ReferenceOutlivesReferent(Ty<'tcx>),
 199
 200     /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
 201     ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 202
 203     /// Obligation incurred due to an object cast.
 204     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 205
 206     /// Obligation incurred due to a coercion.
 207     Coercion {
 208         source: Ty<'tcx>,
 209         target: Ty<'tcx>,
 210     },
 211
 212     /// Various cases where expressions must be `Sized` / `Copy` / etc.
 213     /// `L = X` implies that `L` is `Sized`.
 214     AssignmentLhsSized,
 215     /// `(x1, .., xn)` must be `Sized`.
 216     TupleInitializerSized,
 217     /// `S { ... }` must be `Sized`.
 218     StructInitializerSized,
 219     /// Type of each variable must be `Sized`.
 220     VariableType(hir::HirId),
 221     /// Argument type must be `Sized`.
 222     SizedArgumentType(Option<Span>),
 223     /// Return type must be `Sized`.
 224     SizedReturnType,
 225     /// Yield type must be `Sized`.
 226     SizedYieldType,
 227     /// Inline asm operand type must be `Sized`.
 228     InlineAsmSized,
 229     /// `[T, ..n]` implies that `T` must be `Copy`.
 230     /// If `true`, suggest `const_in_array_repeat_expressions` feature flag.
 231     RepeatVec(bool),
 232
 233     /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
 234     FieldSized {
 235         adt_kind: AdtKind,
 236         span: Span,
 237         last: bool,
 238     },
 239
 240     /// Constant expressions must be sized.
 241     ConstSized,
 242
 243     /// `static` items must have `Sync` type.
 244     SharedStatic,
 245
 246     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 247
 248     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 249
 250     DerivedObligation(DerivedObligationCause<'tcx>),
 251
 252     /// Error derived when matching traits/impls; see ObligationCause for more details
 253     CompareImplConstObligation,
 254
 255     /// Error derived when matching traits/impls; see ObligationCause for more details
 256     CompareImplMethodObligation {
 257         item_name: Symbol,
 258         impl_item_def_id: DefId,
 259         trait_item_def_id: DefId,
 260     },
 261
 262     /// Error derived when matching traits/impls; see ObligationCause for more details
 263     CompareImplTypeObligation {
 264         item_name: Symbol,
 265         impl_item_def_id: DefId,
 266         trait_item_def_id: DefId,
 267     },
 268
 269     /// Checking that this expression can be assigned where it needs to be
 270     // FIXME(eddyb) #11161 is the original Expr required?
 271     ExprAssignable,
 272
 273     /// Computing common supertype in the arms of a match expression
 274     MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
 275
 276     /// Type error arising from type checking a pattern against an expected type.
 277     Pattern {
 278         /// The span of the scrutinee or type expression which caused the `root_ty` type.
 279         span: Option<Span>,
 280         /// The root expected type induced by a scrutinee or type expression.
 281         root_ty: Ty<'tcx>,
 282         /// Whether the `Span` came from an expression or a type expression.
 283         origin_expr: bool,
 284     },
 285
 286     /// Constants in patterns must have `Structural` type.
 287     ConstPatternStructural,
 288
 289     /// Computing common supertype in an if expression
 290     IfExpression(Box<IfExpressionCause>),
 291
 292     /// Computing common supertype of an if expression with no else counter-part
 293     IfExpressionWithNoElse,
 294
 295     /// `main` has wrong type
 296     MainFunctionType,
 297
 298     /// `start` has wrong type
 299     StartFunctionType,
 300
 301     /// Intrinsic has wrong type
 302     IntrinsicType,
 303
 304     /// Method receiver
 305     MethodReceiver,
 306
 307     UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
 308
 309     /// `return` with no expression
 310     ReturnNoExpression,
 311
 312     /// `return` with an expression
 313     ReturnValue(hir::HirId),
 314
 315     /// Return type of this function
 316     ReturnType,
 317
 318     /// Block implicit return
 319     BlockTailExpression(hir::HirId),
 320
 321     /// #[feature(trivial_bounds)] is not enabled
 322     TrivialBound,
 323 }
 324
 325 impl ObligationCauseCode<'_> {
 326     // Return the base obligation, ignoring derived obligations.
 327     pub fn peel_derives(&self) -> &Self {
 328         let mut base_cause = self;
 329         while let BuiltinDerivedObligation(cause)
 330         | ImplDerivedObligation(cause)
 331         | DerivedObligation(cause) = base_cause
 332         {
 333             base_cause = &cause.parent_code;
 334         }
 335         base_cause
 336     }
 337 }
 338
 339 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
 340 #[cfg(target_arch = "x86_64")]
 341 static_assert_size!(ObligationCauseCode<'_>, 32);
 342
 343 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 344 pub enum StatementAsExpression {
 345     CorrectType,
 346     NeedsBoxing,
 347 }
 348
 349 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
 350     type Lifted = StatementAsExpression;
 351     fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
 352         Some(self)
 353     }
 354 }
 355
 356 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 357 pub struct MatchExpressionArmCause<'tcx> {
 358     pub arm_span: Span,
 359     pub scrut_span: Span,
 360     pub semi_span: Option<(Span, StatementAsExpression)>,
 361     pub source: hir::MatchSource,
 362     pub prior_arms: Vec<Span>,
 363     pub last_ty: Ty<'tcx>,
 364     pub scrut_hir_id: hir::HirId,
 365     pub opt_suggest_box_span: Option<Span>,
 366 }
 367
 368 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 369 pub struct IfExpressionCause {
 370     pub then: Span,
 371     pub else_sp: Span,
 372     pub outer: Option<Span>,
 373     pub semicolon: Option<(Span, StatementAsExpression)>,
 374     pub opt_suggest_box_span: Option<Span>,
 375 }
 376
 377 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 378 pub struct DerivedObligationCause<'tcx> {
 379     /// The trait reference of the parent obligation that led to the
 380     /// current obligation. Note that only trait obligations lead to
 381     /// derived obligations, so we just store the trait reference here
 382     /// directly.
 383     pub parent_trait_ref: ty::PolyTraitRef<'tcx>,
 384
 385     /// The parent trait had this cause.
 386     pub parent_code: Rc<ObligationCauseCode<'tcx>>,
 387 }
 388
 389 #[derive(Clone, Debug, TypeFoldable, Lift)]
 390 pub enum SelectionError<'tcx> {
 391     Unimplemented,
 392     OutputTypeParameterMismatch(
 393         ty::PolyTraitRef<'tcx>,
 394         ty::PolyTraitRef<'tcx>,
 395         ty::error::TypeError<'tcx>,
 396     ),
 397     TraitNotObjectSafe(DefId),
 398     ConstEvalFailure(ErrorHandled),
 399     Overflow,
 400 }
 401
 402 /// When performing resolution, it is typically the case that there
 403 /// can be one of three outcomes:
 404 ///
 405 /// - `Ok(Some(r))`: success occurred with result `r`
 406 /// - `Ok(None)`: could not definitely determine anything, usually due
 407 ///   to inconclusive type inference.
 408 /// - `Err(e)`: error `e` occurred
 409 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 410
 411 /// Given the successful resolution of an obligation, the `ImplSource`
 412 /// indicates where the impl comes from.
 413 ///
 414 /// For example, the obligation may be satisfied by a specific impl (case A),
 415 /// or it may be relative to some bound that is in scope (case B).
 416 ///
 417 /// ```
 418 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 419 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 420 /// impl Clone for i32 { ... }                   // Impl_3
 421 ///
 422 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
 423 ///     // Case A: Vtable points at a specific impl. Only possible when
 424 ///     // type is concretely known. If the impl itself has bounded
 425 ///     // type parameters, Vtable will carry resolutions for those as well:
 426 ///     concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 427 ///
 428 ///     // Case A: ImplSource points at a specific impl. Only possible when
 429 ///     // type is concretely known. If the impl itself has bounded
 430 ///     // type parameters, ImplSource will carry resolutions for those as well:
 431 ///     concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
 432 ///
 433 ///     // Case B: ImplSource must be provided by caller. This applies when
 434 ///     // type is a type parameter.
 435 ///     param.clone();    // ImplSource::Param
 436 ///
 437 ///     // Case C: A mix of cases A and B.
 438 ///     mixed.clone();    // ImplSource(Impl_1, [ImplSource::Param])
 439 /// }
 440 /// ```
 441 ///
 442 /// ### The type parameter `N`
 443 ///
 444 /// See explanation on `ImplSourceUserDefinedData`.
 445 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 446 pub enum ImplSource<'tcx, N> {
 447     /// ImplSource identifying a particular impl.
 448     UserDefined(ImplSourceUserDefinedData<'tcx, N>),
 449
 450     /// ImplSource for auto trait implementations.
 451     /// This carries the information and nested obligations with regards
 452     /// to an auto implementation for a trait `Trait`. The nested obligations
 453     /// ensure the trait implementation holds for all the constituent types.
 454     AutoImpl(ImplSourceAutoImplData<N>),
 455
 456     /// Successful resolution to an obligation provided by the caller
 457     /// for some type parameter. The `Vec<N>` represents the
 458     /// obligations incurred from normalizing the where-clause (if
 459     /// any).
 460     Param(Vec<N>),
 461
 462     /// Virtual calls through an object.
 463     Object(ImplSourceObjectData<'tcx, N>),
 464
 465     /// Successful resolution for a builtin trait.
 466     Builtin(ImplSourceBuiltinData<N>),
 467
 468     /// ImplSource automatically generated for a closure. The `DefId` is the ID
 469     /// of the closure expression. This is a `ImplSource::UserDefined` in spirit, but the
 470     /// impl is generated by the compiler and does not appear in the source.
 471     Closure(ImplSourceClosureData<'tcx, N>),
 472
 473     /// Same as above, but for a function pointer type with the given signature.
 474     FnPointer(ImplSourceFnPointerData<'tcx, N>),
 475
 476     /// ImplSource for a builtin `DeterminantKind` trait implementation.
 477     DiscriminantKind(ImplSourceDiscriminantKindData),
 478
 479     /// ImplSource automatically generated for a generator.
 480     Generator(ImplSourceGeneratorData<'tcx, N>),
 481
 482     /// ImplSource for a trait alias.
 483     TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
 484 }
 485
 486 impl<'tcx, N> ImplSource<'tcx, N> {
 487     pub fn nested_obligations(self) -> Vec<N> {
 488         match self {
 489             ImplSource::UserDefined(i) => i.nested,
 490             ImplSource::Param(n) => n,
 491             ImplSource::Builtin(i) => i.nested,
 492             ImplSource::AutoImpl(d) => d.nested,
 493             ImplSource::Closure(c) => c.nested,
 494             ImplSource::Generator(c) => c.nested,
 495             ImplSource::Object(d) => d.nested,
 496             ImplSource::FnPointer(d) => d.nested,
 497             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => Vec::new(),
 498             ImplSource::TraitAlias(d) => d.nested,
 499         }
 500     }
 501
 502     pub fn borrow_nested_obligations(&self) -> &[N] {
 503         match &self {
 504             ImplSource::UserDefined(i) => &i.nested[..],
 505             ImplSource::Param(n) => &n[..],
 506             ImplSource::Builtin(i) => &i.nested[..],
 507             ImplSource::AutoImpl(d) => &d.nested[..],
 508             ImplSource::Closure(c) => &c.nested[..],
 509             ImplSource::Generator(c) => &c.nested[..],
 510             ImplSource::Object(d) => &d.nested[..],
 511             ImplSource::FnPointer(d) => &d.nested[..],
 512             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => &[],
 513             ImplSource::TraitAlias(d) => &d.nested[..],
 514         }
 515     }
 516
 517     pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
 518     where
 519         F: FnMut(N) -> M,
 520     {
 521         match self {
 522             ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
 523                 impl_def_id: i.impl_def_id,
 524                 substs: i.substs,
 525                 nested: i.nested.into_iter().map(f).collect(),
 526             }),
 527             ImplSource::Param(n) => ImplSource::Param(n.into_iter().map(f).collect()),
 528             ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
 529                 nested: i.nested.into_iter().map(f).collect(),
 530             }),
 531             ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
 532                 upcast_trait_ref: o.upcast_trait_ref,
 533                 vtable_base: o.vtable_base,
 534                 nested: o.nested.into_iter().map(f).collect(),
 535             }),
 536             ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
 537                 trait_def_id: d.trait_def_id,
 538                 nested: d.nested.into_iter().map(f).collect(),
 539             }),
 540             ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
 541                 closure_def_id: c.closure_def_id,
 542                 substs: c.substs,
 543                 nested: c.nested.into_iter().map(f).collect(),
 544             }),
 545             ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
 546                 generator_def_id: c.generator_def_id,
 547                 substs: c.substs,
 548                 nested: c.nested.into_iter().map(f).collect(),
 549             }),
 550             ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
 551                 fn_ty: p.fn_ty,
 552                 nested: p.nested.into_iter().map(f).collect(),
 553             }),
 554             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
 555                 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 556             }
 557             ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
 558                 alias_def_id: d.alias_def_id,
 559                 substs: d.substs,
 560                 nested: d.nested.into_iter().map(f).collect(),
 561             }),
 562         }
 563     }
 564 }
 565
 566 /// Identifies a particular impl in the source, along with a set of
 567 /// substitutions from the impl's type/lifetime parameters. The
 568 /// `nested` vector corresponds to the nested obligations attached to
 569 /// the impl's type parameters.
 570 ///
 571 /// The type parameter `N` indicates the type used for "nested
 572 /// obligations" that are required by the impl. During type-check, this
 573 /// is `Obligation`, as one might expect. During codegen, however, this
 574 /// is `()`, because codegen only requires a shallow resolution of an
 575 /// impl, and nested obligations are satisfied later.
 576 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 577 pub struct ImplSourceUserDefinedData<'tcx, N> {
 578     pub impl_def_id: DefId,
 579     pub substs: SubstsRef<'tcx>,
 580     pub nested: Vec<N>,
 581 }
 582
 583 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 584 pub struct ImplSourceGeneratorData<'tcx, N> {
 585     pub generator_def_id: DefId,
 586     pub substs: SubstsRef<'tcx>,
 587     /// Nested obligations. This can be non-empty if the generator
 588     /// signature contains associated types.
 589     pub nested: Vec<N>,
 590 }
 591
 592 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 593 pub struct ImplSourceClosureData<'tcx, N> {
 594     pub closure_def_id: DefId,
 595     pub substs: SubstsRef<'tcx>,
 596     /// Nested obligations. This can be non-empty if the closure
 597     /// signature contains associated types.
 598     pub nested: Vec<N>,
 599 }
 600
 601 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 602 pub struct ImplSourceAutoImplData<N> {
 603     pub trait_def_id: DefId,
 604     pub nested: Vec<N>,
 605 }
 606
 607 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 608 pub struct ImplSourceBuiltinData<N> {
 609     pub nested: Vec<N>,
 610 }
 611
 612 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 613 pub struct ImplSourceObjectData<'tcx, N> {
 614     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 615     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 616
 617     /// The vtable is formed by concatenating together the method lists of
 618     /// the base object trait and all supertraits; this is the start of
 619     /// `upcast_trait_ref`'s methods in that vtable.
 620     pub vtable_base: usize,
 621
 622     pub nested: Vec<N>,
 623 }
 624
 625 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 626 pub struct ImplSourceFnPointerData<'tcx, N> {
 627     pub fn_ty: Ty<'tcx>,
 628     pub nested: Vec<N>,
 629 }
 630
 631 // FIXME(@lcnr): This should be  refactored and merged with other builtin vtables.
 632 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 633 pub struct ImplSourceDiscriminantKindData;
 634
 635 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 636 pub struct ImplSourceTraitAliasData<'tcx, N> {
 637     pub alias_def_id: DefId,
 638     pub substs: SubstsRef<'tcx>,
 639     pub nested: Vec<N>,
 640 }
 641
 642 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 643 pub enum ObjectSafetyViolation {
 644     /// `Self: Sized` declared on the trait.
 645     SizedSelf(SmallVec<[Span; 1]>),
 646
 647     /// Supertrait reference references `Self` an in illegal location
 648     /// (e.g., `trait Foo : Bar<Self>`).
 649     SupertraitSelf(SmallVec<[Span; 1]>),
 650
 651     /// Method has something illegal.
 652     Method(Symbol, MethodViolationCode, Span),
 653
 654     /// Associated const.
 655     AssocConst(Symbol, Span),
 656 }
 657
 658 impl ObjectSafetyViolation {
 659     pub fn error_msg(&self) -> Cow<'static, str> {
 660         match *self {
 661             ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
 662             ObjectSafetyViolation::SupertraitSelf(ref spans) => {
 663                 if spans.iter().any(|sp| *sp != DUMMY_SP) {
 664                     "it uses `Self` as a type parameter".into()
 665                 } else {
 666                     "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
 667                         .into()
 668                 }
 669             }
 670             ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
 671                 format!("associated function `{}` has no `self` parameter", name).into()
 672             }
 673             ObjectSafetyViolation::Method(
 674                 name,
 675                 MethodViolationCode::ReferencesSelfInput(_),
 676                 DUMMY_SP,
 677             ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
 678             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
 679                 format!("method `{}` references the `Self` type in this parameter", name).into()
 680             }
 681             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
 682                 format!("method `{}` references the `Self` type in its return type", name).into()
 683             }
 684             ObjectSafetyViolation::Method(
 685                 name,
 686                 MethodViolationCode::WhereClauseReferencesSelf,
 687                 _,
 688             ) => {
 689                 format!("method `{}` references the `Self` type in its `where` clause", name).into()
 690             }
 691             ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
 692                 format!("method `{}` has generic type parameters", name).into()
 693             }
 694             ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
 695                 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
 696             }
 697             ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
 698                 format!("it contains associated `const` `{}`", name).into()
 699             }
 700             ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
 701         }
 702     }
 703
 704     pub fn solution(&self, err: &mut DiagnosticBuilder<'_>) {
 705         match *self {
 706             ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
 707             ObjectSafetyViolation::Method(
 708                 name,
 709                 MethodViolationCode::StaticMethod(sugg, self_span, has_args),
 710                 _,
 711             ) => {
 712                 err.span_suggestion(
 713                     self_span,
 714                     &format!(
 715                         "consider turning `{}` into a method by giving it a `&self` argument",
 716                         name
 717                     ),
 718                     format!("&self{}", if has_args { ", " } else { "" }),
 719                     Applicability::MaybeIncorrect,
 720                 );
 721                 match sugg {
 722                     Some((sugg, span)) => {
 723                         err.span_suggestion(
 724                             span,
 725                             &format!(
 726                                 "alternatively, consider constraining `{}` so it does not apply to \
 727                                  trait objects",
 728                                 name
 729                             ),
 730                             sugg.to_string(),
 731                             Applicability::MaybeIncorrect,
 732                         );
 733                     }
 734                     None => {
 735                         err.help(&format!(
 736                             "consider turning `{}` into a method by giving it a `&self` \
 737                              argument or constraining it so it does not apply to trait objects",
 738                             name
 739                         ));
 740                     }
 741                 }
 742             }
 743             ObjectSafetyViolation::Method(
 744                 name,
 745                 MethodViolationCode::UndispatchableReceiver,
 746                 span,
 747             ) => {
 748                 err.span_suggestion(
 749                     span,
 750                     &format!(
 751                         "consider changing method `{}`'s `self` parameter to be `&self`",
 752                         name
 753                     ),
 754                     "&Self".to_string(),
 755                     Applicability::MachineApplicable,
 756                 );
 757             }
 758             ObjectSafetyViolation::AssocConst(name, _)
 759             | ObjectSafetyViolation::Method(name, ..) => {
 760                 err.help(&format!("consider moving `{}` to another trait", name));
 761             }
 762         }
 763     }
 764
 765     pub fn spans(&self) -> SmallVec<[Span; 1]> {
 766         // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
 767         // diagnostics use a `note` instead of a `span_label`.
 768         match self {
 769             ObjectSafetyViolation::SupertraitSelf(spans)
 770             | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
 771             ObjectSafetyViolation::AssocConst(_, span)
 772             | ObjectSafetyViolation::Method(_, _, span)
 773                 if *span != DUMMY_SP =>
 774             {
 775                 smallvec![*span]
 776             }
 777             _ => smallvec![],
 778         }
 779     }
 780 }
 781
 782 /// Reasons a method might not be object-safe.
 783 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 784 pub enum MethodViolationCode {
 785     /// e.g., `fn foo()`
 786     StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),
 787
 788     /// e.g., `fn foo(&self, x: Self)`
 789     ReferencesSelfInput(usize),
 790
 791     /// e.g., `fn foo(&self) -> Self`
 792     ReferencesSelfOutput,
 793
 794     /// e.g., `fn foo(&self) where Self: Clone`
 795     WhereClauseReferencesSelf,
 796
 797     /// e.g., `fn foo<A>()`
 798     Generic,
 799
 800     /// the method's receiver (`self` argument) can't be dispatched on
 801     UndispatchableReceiver,
 802 }