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 pub mod util;
  11
  12 use crate::infer::canonical::Canonical;
  13 use crate::thir::abstract_const::NotConstEvaluatable;
  14 use crate::ty::subst::SubstsRef;
  15 use crate::ty::{self, AdtKind, Ty, TyCtxt};
  16
  17 use rustc_data_structures::sync::Lrc;
  18 use rustc_errors::{Applicability, Diagnostic};
  19 use rustc_hir as hir;
  20 use rustc_hir::def_id::{DefId, LocalDefId};
  21 use rustc_span::symbol::Symbol;
  22 use rustc_span::{Span, DUMMY_SP};
  23 use smallvec::SmallVec;
  24
  25 use std::borrow::Cow;
  26 use std::hash::{Hash, Hasher};
  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     /// ```compile_fail,E0308
  51     /// #![feature(specialization)]
  52     /// trait Assoc {
  53     ///     type Output;
  54     /// }
  55     ///
  56     /// impl<T> Assoc for T {
  57     ///     default type Output = bool;
  58     /// }
  59     ///
  60     /// fn main() {
  61     ///     let x: <() as Assoc>::Output = true;
  62     /// }
  63     /// ```
  64     ///
  65     /// We also do not reveal the hidden type of opaque types during
  66     /// type-checking.
  67     UserFacing,
  68
  69     /// At codegen time, all monomorphic projections will succeed.
  70     /// Also, `impl Trait` is normalized to the concrete type,
  71     /// which has to be already collected by type-checking.
  72     ///
  73     /// NOTE: as `impl Trait`'s concrete type should *never*
  74     /// be observable directly by the user, `Reveal::All`
  75     /// should not be used by checks which may expose
  76     /// type equality or type contents to the user.
  77     /// There are some exceptions, e.g., around auto traits and
  78     /// transmute-checking, which expose some details, but
  79     /// not the whole concrete type of the `impl Trait`.
  80     All,
  81 }
  82
  83 /// The reason why we incurred this obligation; used for error reporting.
  84 ///
  85 /// Non-misc `ObligationCauseCode`s are stored on the heap. This gives the
  86 /// best trade-off between keeping the type small (which makes copies cheaper)
  87 /// while not doing too many heap allocations.
  88 ///
  89 /// We do not want to intern this as there are a lot of obligation causes which
  90 /// only live for a short period of time.
  91 #[derive(Clone, Debug, PartialEq, Eq, Lift)]
  92 pub struct ObligationCause<'tcx> {
  93     pub span: Span,
  94
  95     /// The ID of the fn body that triggered this obligation. This is
  96     /// used for region obligations to determine the precise
  97     /// environment in which the region obligation should be evaluated
  98     /// (in particular, closures can add new assumptions). See the
  99     /// field `region_obligations` of the `FulfillmentContext` for more
 100     /// information.
 101     pub body_id: hir::HirId,
 102
 103     code: InternedObligationCauseCode<'tcx>,
 104 }
 105
 106 // This custom hash function speeds up hashing for `Obligation` deduplication
 107 // greatly by skipping the `code` field, which can be large and complex. That
 108 // shouldn't affect hash quality much since there are several other fields in
 109 // `Obligation` which should be unique enough, especially the predicate itself
 110 // which is hashed as an interned pointer. See #90996.
 111 impl Hash for ObligationCause<'_> {
 112     fn hash<H: Hasher>(&self, state: &mut H) {
 113         self.body_id.hash(state);
 114         self.span.hash(state);
 115     }
 116 }
 117
 118 impl<'tcx> ObligationCause<'tcx> {
 119     #[inline]
 120     pub fn new(
 121         span: Span,
 122         body_id: hir::HirId,
 123         code: ObligationCauseCode<'tcx>,
 124     ) -> ObligationCause<'tcx> {
 125         ObligationCause { span, body_id, code: code.into() }
 126     }
 127
 128     pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
 129         ObligationCause::new(span, body_id, MiscObligation)
 130     }
 131
 132     #[inline(always)]
 133     pub fn dummy() -> ObligationCause<'tcx> {
 134         ObligationCause::dummy_with_span(DUMMY_SP)
 135     }
 136
 137     #[inline(always)]
 138     pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
 139         ObligationCause { span, body_id: hir::CRATE_HIR_ID, code: Default::default() }
 140     }
 141
 142     pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
 143         match *self.code() {
 144             ObligationCauseCode::CompareImplMethodObligation { .. }
 145             | ObligationCauseCode::MainFunctionType
 146             | ObligationCauseCode::StartFunctionType => {
 147                 tcx.sess.source_map().guess_head_span(self.span)
 148             }
 149             ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
 150                 arm_span,
 151                 ..
 152             }) => arm_span,
 153             _ => self.span,
 154         }
 155     }
 156
 157     #[inline]
 158     pub fn code(&self) -> &ObligationCauseCode<'tcx> {
 159         &self.code
 160     }
 161
 162     pub fn map_code(
 163         &mut self,
 164         f: impl FnOnce(InternedObligationCauseCode<'tcx>) -> ObligationCauseCode<'tcx>,
 165     ) {
 166         self.code = f(std::mem::take(&mut self.code)).into();
 167     }
 168
 169     pub fn derived_cause(
 170         mut self,
 171         parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
 172         variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,
 173     ) -> ObligationCause<'tcx> {
 174         /*!
 175          * Creates a cause for obligations that are derived from
 176          * `obligation` by a recursive search (e.g., for a builtin
 177          * bound, or eventually a `auto trait Foo`). If `obligation`
 178          * is itself a derived obligation, this is just a clone, but
 179          * otherwise we create a "derived obligation" cause so as to
 180          * keep track of the original root obligation for error
 181          * reporting.
 182          */
 183
 184         // NOTE(flaper87): As of now, it keeps track of the whole error
 185         // chain. Ideally, we should have a way to configure this either
 186         // by using -Z verbose or just a CLI argument.
 187         self.code =
 188             variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into();
 189         self
 190     }
 191 }
 192
 193 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 194 pub struct UnifyReceiverContext<'tcx> {
 195     pub assoc_item: ty::AssocItem,
 196     pub param_env: ty::ParamEnv<'tcx>,
 197     pub substs: SubstsRef<'tcx>,
 198 }
 199
 200 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift, Default)]
 201 pub struct InternedObligationCauseCode<'tcx> {
 202     /// `None` for `ObligationCauseCode::MiscObligation` (a common case, occurs ~60% of
 203     /// the time). `Some` otherwise.
 204     code: Option<Lrc<ObligationCauseCode<'tcx>>>,
 205 }
 206
 207 impl<'tcx> ObligationCauseCode<'tcx> {
 208     #[inline(always)]
 209     fn into(self) -> InternedObligationCauseCode<'tcx> {
 210         InternedObligationCauseCode {
 211             code: if let ObligationCauseCode::MiscObligation = self {
 212                 None
 213             } else {
 214                 Some(Lrc::new(self))
 215             },
 216         }
 217     }
 218 }
 219
 220 impl<'tcx> std::ops::Deref for InternedObligationCauseCode<'tcx> {
 221     type Target = ObligationCauseCode<'tcx>;
 222
 223     fn deref(&self) -> &Self::Target {
 224         self.code.as_deref().unwrap_or(&ObligationCauseCode::MiscObligation)
 225     }
 226 }
 227
 228 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 229 pub enum ObligationCauseCode<'tcx> {
 230     /// Not well classified or should be obvious from the span.
 231     MiscObligation,
 232
 233     /// A slice or array is WF only if `T: Sized`.
 234     SliceOrArrayElem,
 235
 236     /// A tuple is WF only if its middle elements are `Sized`.
 237     TupleElem,
 238
 239     /// This is the trait reference from the given projection.
 240     ProjectionWf(ty::ProjectionTy<'tcx>),
 241
 242     /// In an impl of trait `X` for type `Y`, type `Y` must
 243     /// also implement all supertraits of `X`.
 244     ItemObligation(DefId),
 245
 246     /// Like `ItemObligation`, but with extra detail on the source of the obligation.
 247     BindingObligation(DefId, Span),
 248
 249     /// A type like `&'a T` is WF only if `T: 'a`.
 250     ReferenceOutlivesReferent(Ty<'tcx>),
 251
 252     /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
 253     ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 254
 255     /// Obligation incurred due to an object cast.
 256     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 257
 258     /// Obligation incurred due to a coercion.
 259     Coercion {
 260         source: Ty<'tcx>,
 261         target: Ty<'tcx>,
 262     },
 263
 264     /// Various cases where expressions must be `Sized` / `Copy` / etc.
 265     /// `L = X` implies that `L` is `Sized`.
 266     AssignmentLhsSized,
 267     /// `(x1, .., xn)` must be `Sized`.
 268     TupleInitializerSized,
 269     /// `S { ... }` must be `Sized`.
 270     StructInitializerSized,
 271     /// Type of each variable must be `Sized`.
 272     VariableType(hir::HirId),
 273     /// Argument type must be `Sized`.
 274     SizedArgumentType(Option<Span>),
 275     /// Return type must be `Sized`.
 276     SizedReturnType,
 277     /// Yield type must be `Sized`.
 278     SizedYieldType,
 279     /// Box expression result type must be `Sized`.
 280     SizedBoxType,
 281     /// Inline asm operand type must be `Sized`.
 282     InlineAsmSized,
 283     /// `[expr; N]` requires `type_of(expr): Copy`.
 284     RepeatElementCopy {
 285         /// If element is a `const fn` we display a help message suggesting to move the
 286         /// function call to a new `const` item while saying that `T` doesn't implement `Copy`.
 287         is_const_fn: bool,
 288     },
 289
 290     /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
 291     FieldSized {
 292         adt_kind: AdtKind,
 293         span: Span,
 294         last: bool,
 295     },
 296
 297     /// Constant expressions must be sized.
 298     ConstSized,
 299
 300     /// `static` items must have `Sync` type.
 301     SharedStatic,
 302
 303     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 304
 305     ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>),
 306
 307     DerivedObligation(DerivedObligationCause<'tcx>),
 308
 309     FunctionArgumentObligation {
 310         /// The node of the relevant argument in the function call.
 311         arg_hir_id: hir::HirId,
 312         /// The node of the function call.
 313         call_hir_id: hir::HirId,
 314         /// The obligation introduced by this argument.
 315         parent_code: InternedObligationCauseCode<'tcx>,
 316     },
 317
 318     /// Error derived when matching traits/impls; see ObligationCause for more details
 319     CompareImplConstObligation,
 320
 321     /// Error derived when matching traits/impls; see ObligationCause for more details
 322     CompareImplMethodObligation {
 323         impl_item_def_id: LocalDefId,
 324         trait_item_def_id: DefId,
 325     },
 326
 327     /// Error derived when matching traits/impls; see ObligationCause for more details
 328     CompareImplTypeObligation {
 329         impl_item_def_id: LocalDefId,
 330         trait_item_def_id: DefId,
 331     },
 332
 333     /// Checking that the bounds of a trait's associated type hold for a given impl
 334     CheckAssociatedTypeBounds {
 335         impl_item_def_id: LocalDefId,
 336         trait_item_def_id: DefId,
 337     },
 338
 339     /// Checking that this expression can be assigned to its target.
 340     ExprAssignable,
 341
 342     /// Computing common supertype in the arms of a match expression
 343     MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
 344
 345     /// Type error arising from type checking a pattern against an expected type.
 346     Pattern {
 347         /// The span of the scrutinee or type expression which caused the `root_ty` type.
 348         span: Option<Span>,
 349         /// The root expected type induced by a scrutinee or type expression.
 350         root_ty: Ty<'tcx>,
 351         /// Whether the `Span` came from an expression or a type expression.
 352         origin_expr: bool,
 353     },
 354
 355     /// Constants in patterns must have `Structural` type.
 356     ConstPatternStructural,
 357
 358     /// Computing common supertype in an if expression
 359     IfExpression(Box<IfExpressionCause>),
 360
 361     /// Computing common supertype of an if expression with no else counter-part
 362     IfExpressionWithNoElse,
 363
 364     /// `main` has wrong type
 365     MainFunctionType,
 366
 367     /// `start` has wrong type
 368     StartFunctionType,
 369
 370     /// Intrinsic has wrong type
 371     IntrinsicType,
 372
 373     /// A let else block does not diverge
 374     LetElse,
 375
 376     /// Method receiver
 377     MethodReceiver,
 378
 379     UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
 380
 381     /// `return` with no expression
 382     ReturnNoExpression,
 383
 384     /// `return` with an expression
 385     ReturnValue(hir::HirId),
 386
 387     /// Return type of this function
 388     ReturnType,
 389
 390     /// Opaque return type of this function
 391     OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
 392
 393     /// Block implicit return
 394     BlockTailExpression(hir::HirId),
 395
 396     /// #[feature(trivial_bounds)] is not enabled
 397     TrivialBound,
 398
 399     /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
 400     OpaqueType,
 401
 402     AwaitableExpr(Option<hir::HirId>),
 403
 404     ForLoopIterator,
 405
 406     QuestionMark,
 407
 408     /// Well-formed checking. If a `WellFormedLoc` is provided,
 409     /// then it will be used to eprform HIR-based wf checking
 410     /// after an error occurs, in order to generate a more precise error span.
 411     /// This is purely for diagnostic purposes - it is always
 412     /// correct to use `MiscObligation` instead, or to specify
 413     /// `WellFormed(None)`
 414     WellFormed(Option<WellFormedLoc>),
 415
 416     /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
 417     MatchImpl(ObligationCause<'tcx>, DefId),
 418
 419     BinOp {
 420         rhs_span: Option<Span>,
 421         is_lit: bool,
 422     },
 423 }
 424
 425 /// The 'location' at which we try to perform HIR-based wf checking.
 426 /// This information is used to obtain an `hir::Ty`, which
 427 /// we can walk in order to obtain precise spans for any
 428 /// 'nested' types (e.g. `Foo` in `Option<Foo>`).
 429 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 430 pub enum WellFormedLoc {
 431     /// Use the type of the provided definition.
 432     Ty(LocalDefId),
 433     /// Use the type of the parameter of the provided function.
 434     /// We cannot use `hir::Param`, since the function may
 435     /// not have a body (e.g. a trait method definition)
 436     Param {
 437         /// The function to lookup the parameter in
 438         function: LocalDefId,
 439         /// The index of the parameter to use.
 440         /// Parameters are indexed from 0, with the return type
 441         /// being the last 'parameter'
 442         param_idx: u16,
 443     },
 444 }
 445
 446 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 447 pub struct ImplDerivedObligationCause<'tcx> {
 448     pub derived: DerivedObligationCause<'tcx>,
 449     pub impl_def_id: DefId,
 450     pub span: Span,
 451 }
 452
 453 impl<'tcx> ObligationCauseCode<'tcx> {
 454     // Return the base obligation, ignoring derived obligations.
 455     pub fn peel_derives(&self) -> &Self {
 456         let mut base_cause = self;
 457         while let Some((parent_code, _)) = base_cause.parent() {
 458             base_cause = parent_code;
 459         }
 460         base_cause
 461     }
 462
 463     pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> {
 464         match self {
 465             FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)),
 466             BuiltinDerivedObligation(derived)
 467             | DerivedObligation(derived)
 468             | ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => {
 469                 Some((&derived.parent_code, Some(derived.parent_trait_pred)))
 470             }
 471             _ => None,
 472         }
 473     }
 474 }
 475
 476 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
 477 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 478 static_assert_size!(ObligationCauseCode<'_>, 48);
 479
 480 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 481 pub enum StatementAsExpression {
 482     CorrectType,
 483     NeedsBoxing,
 484 }
 485
 486 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
 487     type Lifted = StatementAsExpression;
 488     fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
 489         Some(self)
 490     }
 491 }
 492
 493 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 494 pub struct MatchExpressionArmCause<'tcx> {
 495     pub arm_span: Span,
 496     pub scrut_span: Span,
 497     pub semi_span: Option<(Span, StatementAsExpression)>,
 498     pub source: hir::MatchSource,
 499     pub prior_arms: Vec<Span>,
 500     pub last_ty: Ty<'tcx>,
 501     pub scrut_hir_id: hir::HirId,
 502     pub opt_suggest_box_span: Option<Span>,
 503 }
 504
 505 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 506 pub struct IfExpressionCause {
 507     pub then: Span,
 508     pub else_sp: Span,
 509     pub outer: Option<Span>,
 510     pub semicolon: Option<(Span, StatementAsExpression)>,
 511     pub opt_suggest_box_span: Option<Span>,
 512 }
 513
 514 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 515 pub struct DerivedObligationCause<'tcx> {
 516     /// The trait predicate of the parent obligation that led to the
 517     /// current obligation. Note that only trait obligations lead to
 518     /// derived obligations, so we just store the trait predicate here
 519     /// directly.
 520     pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
 521
 522     /// The parent trait had this cause.
 523     pub parent_code: InternedObligationCauseCode<'tcx>,
 524 }
 525
 526 #[derive(Clone, Debug, TypeFoldable, Lift)]
 527 pub enum SelectionError<'tcx> {
 528     /// The trait is not implemented.
 529     Unimplemented,
 530     /// After a closure impl has selected, its "outputs" were evaluated
 531     /// (which for closures includes the "input" type params) and they
 532     /// didn't resolve. See `confirm_poly_trait_refs` for more.
 533     OutputTypeParameterMismatch(
 534         ty::PolyTraitRef<'tcx>,
 535         ty::PolyTraitRef<'tcx>,
 536         ty::error::TypeError<'tcx>,
 537     ),
 538     /// The trait pointed by `DefId` is not object safe.
 539     TraitNotObjectSafe(DefId),
 540     /// A given constant couldn't be evaluated.
 541     NotConstEvaluatable(NotConstEvaluatable),
 542     /// Exceeded the recursion depth during type projection.
 543     Overflow(OverflowError),
 544     /// Signaling that an error has already been emitted, to avoid
 545     /// multiple errors being shown.
 546     ErrorReporting,
 547     /// Multiple applicable `impl`s where found. The `DefId`s correspond to
 548     /// all the `impl`s' Items.
 549     Ambiguous(Vec<DefId>),
 550 }
 551
 552 /// When performing resolution, it is typically the case that there
 553 /// can be one of three outcomes:
 554 ///
 555 /// - `Ok(Some(r))`: success occurred with result `r`
 556 /// - `Ok(None)`: could not definitely determine anything, usually due
 557 ///   to inconclusive type inference.
 558 /// - `Err(e)`: error `e` occurred
 559 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 560
 561 /// Given the successful resolution of an obligation, the `ImplSource`
 562 /// indicates where the impl comes from.
 563 ///
 564 /// For example, the obligation may be satisfied by a specific impl (case A),
 565 /// or it may be relative to some bound that is in scope (case B).
 566 ///
 567 /// ```ignore (illustrative)
 568 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 569 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 570 /// impl Clone for i32 { ... }                   // Impl_3
 571 ///
 572 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
 573 ///     // Case A: ImplSource points at a specific impl. Only possible when
 574 ///     // type is concretely known. If the impl itself has bounded
 575 ///     // type parameters, ImplSource will carry resolutions for those as well:
 576 ///     concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
 577 ///
 578 ///     // Case A: ImplSource points at a specific impl. Only possible when
 579 ///     // type is concretely known. If the impl itself has bounded
 580 ///     // type parameters, ImplSource will carry resolutions for those as well:
 581 ///     concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
 582 ///
 583 ///     // Case B: ImplSource must be provided by caller. This applies when
 584 ///     // type is a type parameter.
 585 ///     param.clone();    // ImplSource::Param
 586 ///
 587 ///     // Case C: A mix of cases A and B.
 588 ///     mixed.clone();    // ImplSource(Impl_1, [ImplSource::Param])
 589 /// }
 590 /// ```
 591 ///
 592 /// ### The type parameter `N`
 593 ///
 594 /// See explanation on `ImplSourceUserDefinedData`.
 595 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 596 pub enum ImplSource<'tcx, N> {
 597     /// ImplSource identifying a particular impl.
 598     UserDefined(ImplSourceUserDefinedData<'tcx, N>),
 599
 600     /// ImplSource for auto trait implementations.
 601     /// This carries the information and nested obligations with regards
 602     /// to an auto implementation for a trait `Trait`. The nested obligations
 603     /// ensure the trait implementation holds for all the constituent types.
 604     AutoImpl(ImplSourceAutoImplData<N>),
 605
 606     /// Successful resolution to an obligation provided by the caller
 607     /// for some type parameter. The `Vec<N>` represents the
 608     /// obligations incurred from normalizing the where-clause (if
 609     /// any).
 610     Param(Vec<N>, ty::BoundConstness),
 611
 612     /// Virtual calls through an object.
 613     Object(ImplSourceObjectData<'tcx, N>),
 614
 615     /// Successful resolution for a builtin trait.
 616     Builtin(ImplSourceBuiltinData<N>),
 617
 618     /// ImplSource for trait upcasting coercion
 619     TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
 620
 621     /// ImplSource automatically generated for a closure. The `DefId` is the ID
 622     /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the
 623     /// impl is generated by the compiler and does not appear in the source.
 624     Closure(ImplSourceClosureData<'tcx, N>),
 625
 626     /// Same as above, but for a function pointer type with the given signature.
 627     FnPointer(ImplSourceFnPointerData<'tcx, N>),
 628
 629     /// ImplSource for a builtin `DeterminantKind` trait implementation.
 630     DiscriminantKind(ImplSourceDiscriminantKindData),
 631
 632     /// ImplSource for a builtin `Pointee` trait implementation.
 633     Pointee(ImplSourcePointeeData),
 634
 635     /// ImplSource automatically generated for a generator.
 636     Generator(ImplSourceGeneratorData<'tcx, N>),
 637
 638     /// ImplSource for a trait alias.
 639     TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
 640
 641     /// ImplSource for a `const Drop` implementation.
 642     ConstDestruct(ImplSourceConstDestructData<N>),
 643 }
 644
 645 impl<'tcx, N> ImplSource<'tcx, N> {
 646     pub fn nested_obligations(self) -> Vec<N> {
 647         match self {
 648             ImplSource::UserDefined(i) => i.nested,
 649             ImplSource::Param(n, _) => n,
 650             ImplSource::Builtin(i) => i.nested,
 651             ImplSource::AutoImpl(d) => d.nested,
 652             ImplSource::Closure(c) => c.nested,
 653             ImplSource::Generator(c) => c.nested,
 654             ImplSource::Object(d) => d.nested,
 655             ImplSource::FnPointer(d) => d.nested,
 656             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 657             | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
 658             ImplSource::TraitAlias(d) => d.nested,
 659             ImplSource::TraitUpcasting(d) => d.nested,
 660             ImplSource::ConstDestruct(i) => i.nested,
 661         }
 662     }
 663
 664     pub fn borrow_nested_obligations(&self) -> &[N] {
 665         match &self {
 666             ImplSource::UserDefined(i) => &i.nested[..],
 667             ImplSource::Param(n, _) => &n,
 668             ImplSource::Builtin(i) => &i.nested,
 669             ImplSource::AutoImpl(d) => &d.nested,
 670             ImplSource::Closure(c) => &c.nested,
 671             ImplSource::Generator(c) => &c.nested,
 672             ImplSource::Object(d) => &d.nested,
 673             ImplSource::FnPointer(d) => &d.nested,
 674             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 675             | ImplSource::Pointee(ImplSourcePointeeData) => &[],
 676             ImplSource::TraitAlias(d) => &d.nested,
 677             ImplSource::TraitUpcasting(d) => &d.nested,
 678             ImplSource::ConstDestruct(i) => &i.nested,
 679         }
 680     }
 681
 682     pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
 683     where
 684         F: FnMut(N) -> M,
 685     {
 686         match self {
 687             ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
 688                 impl_def_id: i.impl_def_id,
 689                 substs: i.substs,
 690                 nested: i.nested.into_iter().map(f).collect(),
 691             }),
 692             ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
 693             ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
 694                 nested: i.nested.into_iter().map(f).collect(),
 695             }),
 696             ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
 697                 upcast_trait_ref: o.upcast_trait_ref,
 698                 vtable_base: o.vtable_base,
 699                 nested: o.nested.into_iter().map(f).collect(),
 700             }),
 701             ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
 702                 trait_def_id: d.trait_def_id,
 703                 nested: d.nested.into_iter().map(f).collect(),
 704             }),
 705             ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
 706                 closure_def_id: c.closure_def_id,
 707                 substs: c.substs,
 708                 nested: c.nested.into_iter().map(f).collect(),
 709             }),
 710             ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
 711                 generator_def_id: c.generator_def_id,
 712                 substs: c.substs,
 713                 nested: c.nested.into_iter().map(f).collect(),
 714             }),
 715             ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
 716                 fn_ty: p.fn_ty,
 717                 nested: p.nested.into_iter().map(f).collect(),
 718             }),
 719             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
 720                 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 721             }
 722             ImplSource::Pointee(ImplSourcePointeeData) => {
 723                 ImplSource::Pointee(ImplSourcePointeeData)
 724             }
 725             ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
 726                 alias_def_id: d.alias_def_id,
 727                 substs: d.substs,
 728                 nested: d.nested.into_iter().map(f).collect(),
 729             }),
 730             ImplSource::TraitUpcasting(d) => {
 731                 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
 732                     upcast_trait_ref: d.upcast_trait_ref,
 733                     vtable_vptr_slot: d.vtable_vptr_slot,
 734                     nested: d.nested.into_iter().map(f).collect(),
 735                 })
 736             }
 737             ImplSource::ConstDestruct(i) => {
 738                 ImplSource::ConstDestruct(ImplSourceConstDestructData {
 739                     nested: i.nested.into_iter().map(f).collect(),
 740                 })
 741             }
 742         }
 743     }
 744 }
 745
 746 /// Identifies a particular impl in the source, along with a set of
 747 /// substitutions from the impl's type/lifetime parameters. The
 748 /// `nested` vector corresponds to the nested obligations attached to
 749 /// the impl's type parameters.
 750 ///
 751 /// The type parameter `N` indicates the type used for "nested
 752 /// obligations" that are required by the impl. During type-check, this
 753 /// is `Obligation`, as one might expect. During codegen, however, this
 754 /// is `()`, because codegen only requires a shallow resolution of an
 755 /// impl, and nested obligations are satisfied later.
 756 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 757 pub struct ImplSourceUserDefinedData<'tcx, N> {
 758     pub impl_def_id: DefId,
 759     pub substs: SubstsRef<'tcx>,
 760     pub nested: Vec<N>,
 761 }
 762
 763 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 764 pub struct ImplSourceGeneratorData<'tcx, N> {
 765     pub generator_def_id: DefId,
 766     pub substs: SubstsRef<'tcx>,
 767     /// Nested obligations. This can be non-empty if the generator
 768     /// signature contains associated types.
 769     pub nested: Vec<N>,
 770 }
 771
 772 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 773 pub struct ImplSourceClosureData<'tcx, N> {
 774     pub closure_def_id: DefId,
 775     pub substs: SubstsRef<'tcx>,
 776     /// Nested obligations. This can be non-empty if the closure
 777     /// signature contains associated types.
 778     pub nested: Vec<N>,
 779 }
 780
 781 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 782 pub struct ImplSourceAutoImplData<N> {
 783     pub trait_def_id: DefId,
 784     pub nested: Vec<N>,
 785 }
 786
 787 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 788 pub struct ImplSourceTraitUpcastingData<'tcx, N> {
 789     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 790     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 791
 792     /// The vtable is formed by concatenating together the method lists of
 793     /// the base object trait and all supertraits, pointers to supertrait vtable will
 794     /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
 795     /// within that vtable.
 796     pub vtable_vptr_slot: Option<usize>,
 797
 798     pub nested: Vec<N>,
 799 }
 800
 801 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 802 pub struct ImplSourceBuiltinData<N> {
 803     pub nested: Vec<N>,
 804 }
 805
 806 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 807 pub struct ImplSourceObjectData<'tcx, N> {
 808     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 809     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 810
 811     /// The vtable is formed by concatenating together the method lists of
 812     /// the base object trait and all supertraits, pointers to supertrait vtable will
 813     /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
 814     /// in that vtable.
 815     pub vtable_base: usize,
 816
 817     pub nested: Vec<N>,
 818 }
 819
 820 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 821 pub struct ImplSourceFnPointerData<'tcx, N> {
 822     pub fn_ty: Ty<'tcx>,
 823     pub nested: Vec<N>,
 824 }
 825
 826 // FIXME(@lcnr): This should be  refactored and merged with other builtin vtables.
 827 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 828 pub struct ImplSourceDiscriminantKindData;
 829
 830 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 831 pub struct ImplSourcePointeeData;
 832
 833 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 834 pub struct ImplSourceConstDestructData<N> {
 835     pub nested: Vec<N>,
 836 }
 837
 838 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 839 pub struct ImplSourceTraitAliasData<'tcx, N> {
 840     pub alias_def_id: DefId,
 841     pub substs: SubstsRef<'tcx>,
 842     pub nested: Vec<N>,
 843 }
 844
 845 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 846 pub enum ObjectSafetyViolation {
 847     /// `Self: Sized` declared on the trait.
 848     SizedSelf(SmallVec<[Span; 1]>),
 849
 850     /// Supertrait reference references `Self` an in illegal location
 851     /// (e.g., `trait Foo : Bar<Self>`).
 852     SupertraitSelf(SmallVec<[Span; 1]>),
 853
 854     /// Method has something illegal.
 855     Method(Symbol, MethodViolationCode, Span),
 856
 857     /// Associated const.
 858     AssocConst(Symbol, Span),
 859
 860     /// GAT
 861     GAT(Symbol, Span),
 862 }
 863
 864 impl ObjectSafetyViolation {
 865     pub fn error_msg(&self) -> Cow<'static, str> {
 866         match *self {
 867             ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
 868             ObjectSafetyViolation::SupertraitSelf(ref spans) => {
 869                 if spans.iter().any(|sp| *sp != DUMMY_SP) {
 870                     "it uses `Self` as a type parameter".into()
 871                 } else {
 872                     "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
 873                         .into()
 874                 }
 875             }
 876             ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
 877                 format!("associated function `{}` has no `self` parameter", name).into()
 878             }
 879             ObjectSafetyViolation::Method(
 880                 name,
 881                 MethodViolationCode::ReferencesSelfInput(_),
 882                 DUMMY_SP,
 883             ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
 884             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
 885                 format!("method `{}` references the `Self` type in this parameter", name).into()
 886             }
 887             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
 888                 format!("method `{}` references the `Self` type in its return type", name).into()
 889             }
 890             ObjectSafetyViolation::Method(
 891                 name,
 892                 MethodViolationCode::WhereClauseReferencesSelf,
 893                 _,
 894             ) => {
 895                 format!("method `{}` references the `Self` type in its `where` clause", name).into()
 896             }
 897             ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
 898                 format!("method `{}` has generic type parameters", name).into()
 899             }
 900             ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
 901                 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
 902             }
 903             ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
 904                 format!("it contains associated `const` `{}`", name).into()
 905             }
 906             ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
 907             ObjectSafetyViolation::GAT(name, _) => {
 908                 format!("it contains the generic associated type `{}`", name).into()
 909             }
 910         }
 911     }
 912
 913     pub fn solution(&self, err: &mut Diagnostic) {
 914         match *self {
 915             ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
 916             ObjectSafetyViolation::Method(
 917                 name,
 918                 MethodViolationCode::StaticMethod(sugg, self_span, has_args),
 919                 _,
 920             ) => {
 921                 err.span_suggestion(
 922                     self_span,
 923                     &format!(
 924                         "consider turning `{}` into a method by giving it a `&self` argument",
 925                         name
 926                     ),
 927                     format!("&self{}", if has_args { ", " } else { "" }),
 928                     Applicability::MaybeIncorrect,
 929                 );
 930                 match sugg {
 931                     Some((sugg, span)) => {
 932                         err.span_suggestion(
 933                             span,
 934                             &format!(
 935                                 "alternatively, consider constraining `{}` so it does not apply to \
 936                                  trait objects",
 937                                 name
 938                             ),
 939                             sugg,
 940                             Applicability::MaybeIncorrect,
 941                         );
 942                     }
 943                     None => {
 944                         err.help(&format!(
 945                             "consider turning `{}` into a method by giving it a `&self` \
 946                              argument or constraining it so it does not apply to trait objects",
 947                             name
 948                         ));
 949                     }
 950                 }
 951             }
 952             ObjectSafetyViolation::Method(
 953                 name,
 954                 MethodViolationCode::UndispatchableReceiver,
 955                 span,
 956             ) => {
 957                 err.span_suggestion(
 958                     span,
 959                     &format!(
 960                         "consider changing method `{}`'s `self` parameter to be `&self`",
 961                         name
 962                     ),
 963                     "&Self",
 964                     Applicability::MachineApplicable,
 965                 );
 966             }
 967             ObjectSafetyViolation::AssocConst(name, _)
 968             | ObjectSafetyViolation::GAT(name, _)
 969             | ObjectSafetyViolation::Method(name, ..) => {
 970                 err.help(&format!("consider moving `{}` to another trait", name));
 971             }
 972         }
 973     }
 974
 975     pub fn spans(&self) -> SmallVec<[Span; 1]> {
 976         // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
 977         // diagnostics use a `note` instead of a `span_label`.
 978         match self {
 979             ObjectSafetyViolation::SupertraitSelf(spans)
 980             | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
 981             ObjectSafetyViolation::AssocConst(_, span)
 982             | ObjectSafetyViolation::GAT(_, span)
 983             | ObjectSafetyViolation::Method(_, _, span)
 984                 if *span != DUMMY_SP =>
 985             {
 986                 smallvec![*span]
 987             }
 988             _ => smallvec![],
 989         }
 990     }
 991 }
 992
 993 /// Reasons a method might not be object-safe.
 994 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 995 pub enum MethodViolationCode {
 996     /// e.g., `fn foo()`
 997     StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),
 998
 999     /// e.g., `fn foo(&self, x: Self)`
1000     ReferencesSelfInput(usize),
1001
1002     /// e.g., `fn foo(&self) -> Self`
1003     ReferencesSelfOutput,
1004
1005     /// e.g., `fn foo(&self) where Self: Clone`
1006     WhereClauseReferencesSelf,
1007
1008     /// e.g., `fn foo<A>()`
1009     Generic,
1010
1011     /// the method's receiver (`self` argument) can't be dispatched on
1012     UndispatchableReceiver,
1013 }
1014
1015 /// These are the error cases for `codegen_fulfill_obligation`.
1016 #[derive(Copy, Clone, Debug, Hash, HashStable, Encodable, Decodable)]
1017 pub enum CodegenObligationError {
1018     /// Ambiguity can happen when monomorphizing during trans
1019     /// expands to some humongous type that never occurred
1020     /// statically -- this humongous type can then overflow,
1021     /// leading to an ambiguous result. So report this as an
1022     /// overflow bug, since I believe this is the only case
1023     /// where ambiguity can result.
1024     Ambiguity,
1025     /// This can trigger when we probe for the source of a `'static` lifetime requirement
1026     /// on a trait object: `impl Foo for dyn Trait {}` has an implicit `'static` bound.
1027     /// This can also trigger when we have a global bound that is not actually satisfied,
1028     /// but was included during typeck due to the trivial_bounds feature.
1029     Unimplemented,
1030     FulfillmentError,
1031 }