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::abstract_const::NotConstEvaluatable;
  13 use crate::ty::subst::SubstsRef;
  14 use crate::ty::{self, AdtKind, Ty, TyCtxt};
  15
  16 use rustc_data_structures::sync::Lrc;
  17 use rustc_errors::{Applicability, DiagnosticBuilder};
  18 use rustc_hir as hir;
  19 use rustc_hir::def_id::{DefId, LocalDefId};
  20 use rustc_span::symbol::Symbol;
  21 use rustc_span::{Span, DUMMY_SP};
  22 use smallvec::SmallVec;
  23
  24 use std::borrow::Cow;
  25 use std::fmt;
  26 use std::ops::Deref;
  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 auto traits 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<Lrc<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(Lrc::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         Lrc::make_mut(self.data.get_or_insert_with(|| Lrc::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     /// Box expression result type must be `Sized`.
 228     SizedBoxType,
 229     /// Inline asm operand type must be `Sized`.
 230     InlineAsmSized,
 231     /// `[T, ..n]` implies that `T` must be `Copy`.
 232     /// If the function in the array repeat expression is a `const fn`,
 233     /// display a help message suggesting to move the function call to a
 234     /// new `const` item while saying that `T` doesn't implement `Copy`.
 235     RepeatVec(bool),
 236
 237     /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
 238     FieldSized {
 239         adt_kind: AdtKind,
 240         span: Span,
 241         last: bool,
 242     },
 243
 244     /// Constant expressions must be sized.
 245     ConstSized,
 246
 247     /// `static` items must have `Sync` type.
 248     SharedStatic,
 249
 250     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 251
 252     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 253
 254     DerivedObligation(DerivedObligationCause<'tcx>),
 255
 256     /// Error derived when matching traits/impls; see ObligationCause for more details
 257     CompareImplConstObligation,
 258
 259     /// Error derived when matching traits/impls; see ObligationCause for more details
 260     CompareImplMethodObligation {
 261         item_name: Symbol,
 262         impl_item_def_id: DefId,
 263         trait_item_def_id: DefId,
 264     },
 265
 266     /// Error derived when matching traits/impls; see ObligationCause for more details
 267     CompareImplTypeObligation {
 268         item_name: Symbol,
 269         impl_item_def_id: DefId,
 270         trait_item_def_id: DefId,
 271     },
 272
 273     /// Checking that this expression can be assigned where it needs to be
 274     // FIXME(eddyb) #11161 is the original Expr required?
 275     ExprAssignable,
 276
 277     /// Computing common supertype in the arms of a match expression
 278     MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
 279
 280     /// Type error arising from type checking a pattern against an expected type.
 281     Pattern {
 282         /// The span of the scrutinee or type expression which caused the `root_ty` type.
 283         span: Option<Span>,
 284         /// The root expected type induced by a scrutinee or type expression.
 285         root_ty: Ty<'tcx>,
 286         /// Whether the `Span` came from an expression or a type expression.
 287         origin_expr: bool,
 288     },
 289
 290     /// Constants in patterns must have `Structural` type.
 291     ConstPatternStructural,
 292
 293     /// Computing common supertype in an if expression
 294     IfExpression(Box<IfExpressionCause>),
 295
 296     /// Computing common supertype of an if expression with no else counter-part
 297     IfExpressionWithNoElse,
 298
 299     /// `main` has wrong type
 300     MainFunctionType,
 301
 302     /// `start` has wrong type
 303     StartFunctionType,
 304
 305     /// Intrinsic has wrong type
 306     IntrinsicType,
 307
 308     /// A let else block does not diverge
 309     LetElse,
 310
 311     /// Method receiver
 312     MethodReceiver,
 313
 314     UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
 315
 316     /// `return` with no expression
 317     ReturnNoExpression,
 318
 319     /// `return` with an expression
 320     ReturnValue(hir::HirId),
 321
 322     /// Return type of this function
 323     ReturnType,
 324
 325     /// Block implicit return
 326     BlockTailExpression(hir::HirId),
 327
 328     /// #[feature(trivial_bounds)] is not enabled
 329     TrivialBound,
 330
 331     /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
 332     OpaqueType,
 333
 334     /// Well-formed checking. If a `WellFormedLoc` is provided,
 335     /// then it will be used to eprform HIR-based wf checking
 336     /// after an error occurs, in order to generate a more precise error span.
 337     /// This is purely for diagnostic purposes - it is always
 338     /// correct to use `MiscObligation` instead, or to specify
 339     /// `WellFormed(None)`
 340     WellFormed(Option<WellFormedLoc>),
 341
 342     /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
 343     MatchImpl(Lrc<ObligationCauseCode<'tcx>>, DefId),
 344 }
 345
 346 /// The 'location' at which we try to perform HIR-based wf checking.
 347 /// This information is used to obtain an `hir::Ty`, which
 348 /// we can walk in order to obtain precise spans for any
 349 /// 'nested' types (e.g. `Foo` in `Option<Foo>`).
 350 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 351 pub enum WellFormedLoc {
 352     /// Use the type of the provided definition.
 353     Ty(LocalDefId),
 354     /// Use the type of the parameter of the provided function.
 355     /// We cannot use `hir::Param`, since the function may
 356     /// not have a body (e.g. a trait method definition)
 357     Param {
 358         /// The function to lookup the parameter in
 359         function: LocalDefId,
 360         /// The index of the parameter to use.
 361         /// Parameters are indexed from 0, with the return type
 362         /// being the last 'parameter'
 363         param_idx: u16,
 364     },
 365 }
 366
 367 impl ObligationCauseCode<'_> {
 368     // Return the base obligation, ignoring derived obligations.
 369     pub fn peel_derives(&self) -> &Self {
 370         let mut base_cause = self;
 371         while let BuiltinDerivedObligation(cause)
 372         | ImplDerivedObligation(cause)
 373         | DerivedObligation(cause) = base_cause
 374         {
 375             base_cause = &cause.parent_code;
 376         }
 377         base_cause
 378     }
 379 }
 380
 381 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
 382 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 383 static_assert_size!(ObligationCauseCode<'_>, 40);
 384
 385 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 386 pub enum StatementAsExpression {
 387     CorrectType,
 388     NeedsBoxing,
 389 }
 390
 391 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
 392     type Lifted = StatementAsExpression;
 393     fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
 394         Some(self)
 395     }
 396 }
 397
 398 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 399 pub struct MatchExpressionArmCause<'tcx> {
 400     pub arm_span: Span,
 401     pub scrut_span: Span,
 402     pub semi_span: Option<(Span, StatementAsExpression)>,
 403     pub source: hir::MatchSource,
 404     pub prior_arms: Vec<Span>,
 405     pub last_ty: Ty<'tcx>,
 406     pub scrut_hir_id: hir::HirId,
 407     pub opt_suggest_box_span: Option<Span>,
 408 }
 409
 410 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 411 pub struct IfExpressionCause {
 412     pub then: Span,
 413     pub else_sp: Span,
 414     pub outer: Option<Span>,
 415     pub semicolon: Option<(Span, StatementAsExpression)>,
 416     pub opt_suggest_box_span: Option<Span>,
 417 }
 418
 419 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
 420 pub struct DerivedObligationCause<'tcx> {
 421     /// The trait reference of the parent obligation that led to the
 422     /// current obligation. Note that only trait obligations lead to
 423     /// derived obligations, so we just store the trait reference here
 424     /// directly.
 425     pub parent_trait_ref: ty::PolyTraitRef<'tcx>,
 426
 427     /// The parent trait had this cause.
 428     pub parent_code: Lrc<ObligationCauseCode<'tcx>>,
 429 }
 430
 431 #[derive(Clone, Debug, TypeFoldable, Lift)]
 432 pub enum SelectionError<'tcx> {
 433     Unimplemented,
 434     OutputTypeParameterMismatch(
 435         ty::PolyTraitRef<'tcx>,
 436         ty::PolyTraitRef<'tcx>,
 437         ty::error::TypeError<'tcx>,
 438     ),
 439     TraitNotObjectSafe(DefId),
 440     NotConstEvaluatable(NotConstEvaluatable),
 441     Overflow,
 442 }
 443
 444 /// When performing resolution, it is typically the case that there
 445 /// can be one of three outcomes:
 446 ///
 447 /// - `Ok(Some(r))`: success occurred with result `r`
 448 /// - `Ok(None)`: could not definitely determine anything, usually due
 449 ///   to inconclusive type inference.
 450 /// - `Err(e)`: error `e` occurred
 451 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 452
 453 /// Given the successful resolution of an obligation, the `ImplSource`
 454 /// indicates where the impl comes from.
 455 ///
 456 /// For example, the obligation may be satisfied by a specific impl (case A),
 457 /// or it may be relative to some bound that is in scope (case B).
 458 ///
 459 /// ```
 460 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 461 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 462 /// impl Clone for i32 { ... }                   // Impl_3
 463 ///
 464 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
 465 ///     // Case A: ImplSource points at a specific impl. Only possible when
 466 ///     // type is concretely known. If the impl itself has bounded
 467 ///     // type parameters, ImplSource will carry resolutions for those as well:
 468 ///     concrete.clone(); // ImpleSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
 469 ///
 470 ///     // Case A: ImplSource points at a specific impl. Only possible when
 471 ///     // type is concretely known. If the impl itself has bounded
 472 ///     // type parameters, ImplSource will carry resolutions for those as well:
 473 ///     concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
 474 ///
 475 ///     // Case B: ImplSource must be provided by caller. This applies when
 476 ///     // type is a type parameter.
 477 ///     param.clone();    // ImplSource::Param
 478 ///
 479 ///     // Case C: A mix of cases A and B.
 480 ///     mixed.clone();    // ImplSource(Impl_1, [ImplSource::Param])
 481 /// }
 482 /// ```
 483 ///
 484 /// ### The type parameter `N`
 485 ///
 486 /// See explanation on `ImplSourceUserDefinedData`.
 487 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 488 pub enum ImplSource<'tcx, N> {
 489     /// ImplSource identifying a particular impl.
 490     UserDefined(ImplSourceUserDefinedData<'tcx, N>),
 491
 492     /// ImplSource for auto trait implementations.
 493     /// This carries the information and nested obligations with regards
 494     /// to an auto implementation for a trait `Trait`. The nested obligations
 495     /// ensure the trait implementation holds for all the constituent types.
 496     AutoImpl(ImplSourceAutoImplData<N>),
 497
 498     /// Successful resolution to an obligation provided by the caller
 499     /// for some type parameter. The `Vec<N>` represents the
 500     /// obligations incurred from normalizing the where-clause (if
 501     /// any).
 502     Param(Vec<N>, ty::BoundConstness),
 503
 504     /// Virtual calls through an object.
 505     Object(ImplSourceObjectData<'tcx, N>),
 506
 507     /// Successful resolution for a builtin trait.
 508     Builtin(ImplSourceBuiltinData<N>),
 509
 510     /// ImplSource for trait upcasting coercion
 511     TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
 512
 513     /// ImplSource automatically generated for a closure. The `DefId` is the ID
 514     /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the
 515     /// impl is generated by the compiler and does not appear in the source.
 516     Closure(ImplSourceClosureData<'tcx, N>),
 517
 518     /// Same as above, but for a function pointer type with the given signature.
 519     FnPointer(ImplSourceFnPointerData<'tcx, N>),
 520
 521     /// ImplSource for a builtin `DeterminantKind` trait implementation.
 522     DiscriminantKind(ImplSourceDiscriminantKindData),
 523
 524     /// ImplSource for a builtin `Pointee` trait implementation.
 525     Pointee(ImplSourcePointeeData),
 526
 527     /// ImplSource automatically generated for a generator.
 528     Generator(ImplSourceGeneratorData<'tcx, N>),
 529
 530     /// ImplSource for a trait alias.
 531     TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
 532 }
 533
 534 impl<'tcx, N> ImplSource<'tcx, N> {
 535     pub fn nested_obligations(self) -> Vec<N> {
 536         match self {
 537             ImplSource::UserDefined(i) => i.nested,
 538             ImplSource::Param(n, _) => n,
 539             ImplSource::Builtin(i) => i.nested,
 540             ImplSource::AutoImpl(d) => d.nested,
 541             ImplSource::Closure(c) => c.nested,
 542             ImplSource::Generator(c) => c.nested,
 543             ImplSource::Object(d) => d.nested,
 544             ImplSource::FnPointer(d) => d.nested,
 545             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 546             | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
 547             ImplSource::TraitAlias(d) => d.nested,
 548             ImplSource::TraitUpcasting(d) => d.nested,
 549         }
 550     }
 551
 552     pub fn borrow_nested_obligations(&self) -> &[N] {
 553         match &self {
 554             ImplSource::UserDefined(i) => &i.nested[..],
 555             ImplSource::Param(n, _) => &n[..],
 556             ImplSource::Builtin(i) => &i.nested[..],
 557             ImplSource::AutoImpl(d) => &d.nested[..],
 558             ImplSource::Closure(c) => &c.nested[..],
 559             ImplSource::Generator(c) => &c.nested[..],
 560             ImplSource::Object(d) => &d.nested[..],
 561             ImplSource::FnPointer(d) => &d.nested[..],
 562             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 563             | ImplSource::Pointee(ImplSourcePointeeData) => &[],
 564             ImplSource::TraitAlias(d) => &d.nested[..],
 565             ImplSource::TraitUpcasting(d) => &d.nested[..],
 566         }
 567     }
 568
 569     pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
 570     where
 571         F: FnMut(N) -> M,
 572     {
 573         match self {
 574             ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
 575                 impl_def_id: i.impl_def_id,
 576                 substs: i.substs,
 577                 nested: i.nested.into_iter().map(f).collect(),
 578             }),
 579             ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
 580             ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
 581                 nested: i.nested.into_iter().map(f).collect(),
 582             }),
 583             ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
 584                 upcast_trait_ref: o.upcast_trait_ref,
 585                 vtable_base: o.vtable_base,
 586                 nested: o.nested.into_iter().map(f).collect(),
 587             }),
 588             ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
 589                 trait_def_id: d.trait_def_id,
 590                 nested: d.nested.into_iter().map(f).collect(),
 591             }),
 592             ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
 593                 closure_def_id: c.closure_def_id,
 594                 substs: c.substs,
 595                 nested: c.nested.into_iter().map(f).collect(),
 596             }),
 597             ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
 598                 generator_def_id: c.generator_def_id,
 599                 substs: c.substs,
 600                 nested: c.nested.into_iter().map(f).collect(),
 601             }),
 602             ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
 603                 fn_ty: p.fn_ty,
 604                 nested: p.nested.into_iter().map(f).collect(),
 605             }),
 606             ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
 607                 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
 608             }
 609             ImplSource::Pointee(ImplSourcePointeeData) => {
 610                 ImplSource::Pointee(ImplSourcePointeeData)
 611             }
 612             ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
 613                 alias_def_id: d.alias_def_id,
 614                 substs: d.substs,
 615                 nested: d.nested.into_iter().map(f).collect(),
 616             }),
 617             ImplSource::TraitUpcasting(d) => {
 618                 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
 619                     upcast_trait_ref: d.upcast_trait_ref,
 620                     vtable_vptr_slot: d.vtable_vptr_slot,
 621                     nested: d.nested.into_iter().map(f).collect(),
 622                 })
 623             }
 624         }
 625     }
 626 }
 627
 628 /// Identifies a particular impl in the source, along with a set of
 629 /// substitutions from the impl's type/lifetime parameters. The
 630 /// `nested` vector corresponds to the nested obligations attached to
 631 /// the impl's type parameters.
 632 ///
 633 /// The type parameter `N` indicates the type used for "nested
 634 /// obligations" that are required by the impl. During type-check, this
 635 /// is `Obligation`, as one might expect. During codegen, however, this
 636 /// is `()`, because codegen only requires a shallow resolution of an
 637 /// impl, and nested obligations are satisfied later.
 638 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 639 pub struct ImplSourceUserDefinedData<'tcx, N> {
 640     pub impl_def_id: DefId,
 641     pub substs: SubstsRef<'tcx>,
 642     pub nested: Vec<N>,
 643 }
 644
 645 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 646 pub struct ImplSourceGeneratorData<'tcx, N> {
 647     pub generator_def_id: DefId,
 648     pub substs: SubstsRef<'tcx>,
 649     /// Nested obligations. This can be non-empty if the generator
 650     /// signature contains associated types.
 651     pub nested: Vec<N>,
 652 }
 653
 654 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 655 pub struct ImplSourceClosureData<'tcx, N> {
 656     pub closure_def_id: DefId,
 657     pub substs: SubstsRef<'tcx>,
 658     /// Nested obligations. This can be non-empty if the closure
 659     /// signature contains associated types.
 660     pub nested: Vec<N>,
 661 }
 662
 663 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 664 pub struct ImplSourceAutoImplData<N> {
 665     pub trait_def_id: DefId,
 666     pub nested: Vec<N>,
 667 }
 668
 669 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 670 pub struct ImplSourceTraitUpcastingData<'tcx, N> {
 671     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 672     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 673
 674     /// The vtable is formed by concatenating together the method lists of
 675     /// the base object trait and all supertraits, pointers to supertrait vtable will
 676     /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
 677     /// within that vtable.
 678     pub vtable_vptr_slot: Option<usize>,
 679
 680     pub nested: Vec<N>,
 681 }
 682
 683 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 684 pub struct ImplSourceBuiltinData<N> {
 685     pub nested: Vec<N>,
 686 }
 687
 688 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 689 pub struct ImplSourceObjectData<'tcx, N> {
 690     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 691     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 692
 693     /// The vtable is formed by concatenating together the method lists of
 694     /// the base object trait and all supertraits, pointers to supertrait vtable will
 695     /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
 696     /// in that vtable.
 697     pub vtable_base: usize,
 698
 699     pub nested: Vec<N>,
 700 }
 701
 702 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 703 pub struct ImplSourceFnPointerData<'tcx, N> {
 704     pub fn_ty: Ty<'tcx>,
 705     pub nested: Vec<N>,
 706 }
 707
 708 // FIXME(@lcnr): This should be  refactored and merged with other builtin vtables.
 709 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 710 pub struct ImplSourceDiscriminantKindData;
 711
 712 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
 713 pub struct ImplSourcePointeeData;
 714
 715 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
 716 pub struct ImplSourceTraitAliasData<'tcx, N> {
 717     pub alias_def_id: DefId,
 718     pub substs: SubstsRef<'tcx>,
 719     pub nested: Vec<N>,
 720 }
 721
 722 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 723 pub enum ObjectSafetyViolation {
 724     /// `Self: Sized` declared on the trait.
 725     SizedSelf(SmallVec<[Span; 1]>),
 726
 727     /// Supertrait reference references `Self` an in illegal location
 728     /// (e.g., `trait Foo : Bar<Self>`).
 729     SupertraitSelf(SmallVec<[Span; 1]>),
 730
 731     /// Method has something illegal.
 732     Method(Symbol, MethodViolationCode, Span),
 733
 734     /// Associated const.
 735     AssocConst(Symbol, Span),
 736
 737     /// GAT
 738     GAT(Symbol, Span),
 739 }
 740
 741 impl ObjectSafetyViolation {
 742     pub fn error_msg(&self) -> Cow<'static, str> {
 743         match *self {
 744             ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
 745             ObjectSafetyViolation::SupertraitSelf(ref spans) => {
 746                 if spans.iter().any(|sp| *sp != DUMMY_SP) {
 747                     "it uses `Self` as a type parameter".into()
 748                 } else {
 749                     "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
 750                         .into()
 751                 }
 752             }
 753             ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
 754                 format!("associated function `{}` has no `self` parameter", name).into()
 755             }
 756             ObjectSafetyViolation::Method(
 757                 name,
 758                 MethodViolationCode::ReferencesSelfInput(_),
 759                 DUMMY_SP,
 760             ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
 761             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
 762                 format!("method `{}` references the `Self` type in this parameter", name).into()
 763             }
 764             ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
 765                 format!("method `{}` references the `Self` type in its return type", name).into()
 766             }
 767             ObjectSafetyViolation::Method(
 768                 name,
 769                 MethodViolationCode::WhereClauseReferencesSelf,
 770                 _,
 771             ) => {
 772                 format!("method `{}` references the `Self` type in its `where` clause", name).into()
 773             }
 774             ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
 775                 format!("method `{}` has generic type parameters", name).into()
 776             }
 777             ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
 778                 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
 779             }
 780             ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
 781                 format!("it contains associated `const` `{}`", name).into()
 782             }
 783             ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
 784             ObjectSafetyViolation::GAT(name, _) => {
 785                 format!("it contains the generic associated type `{}`", name).into()
 786             }
 787         }
 788     }
 789
 790     pub fn solution(&self, err: &mut DiagnosticBuilder<'_>) {
 791         match *self {
 792             ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
 793             ObjectSafetyViolation::Method(
 794                 name,
 795                 MethodViolationCode::StaticMethod(sugg, self_span, has_args),
 796                 _,
 797             ) => {
 798                 err.span_suggestion(
 799                     self_span,
 800                     &format!(
 801                         "consider turning `{}` into a method by giving it a `&self` argument",
 802                         name
 803                     ),
 804                     format!("&self{}", if has_args { ", " } else { "" }),
 805                     Applicability::MaybeIncorrect,
 806                 );
 807                 match sugg {
 808                     Some((sugg, span)) => {
 809                         err.span_suggestion(
 810                             span,
 811                             &format!(
 812                                 "alternatively, consider constraining `{}` so it does not apply to \
 813                                  trait objects",
 814                                 name
 815                             ),
 816                             sugg.to_string(),
 817                             Applicability::MaybeIncorrect,
 818                         );
 819                     }
 820                     None => {
 821                         err.help(&format!(
 822                             "consider turning `{}` into a method by giving it a `&self` \
 823                              argument or constraining it so it does not apply to trait objects",
 824                             name
 825                         ));
 826                     }
 827                 }
 828             }
 829             ObjectSafetyViolation::Method(
 830                 name,
 831                 MethodViolationCode::UndispatchableReceiver,
 832                 span,
 833             ) => {
 834                 err.span_suggestion(
 835                     span,
 836                     &format!(
 837                         "consider changing method `{}`'s `self` parameter to be `&self`",
 838                         name
 839                     ),
 840                     "&Self".to_string(),
 841                     Applicability::MachineApplicable,
 842                 );
 843             }
 844             ObjectSafetyViolation::AssocConst(name, _)
 845             | ObjectSafetyViolation::GAT(name, _)
 846             | ObjectSafetyViolation::Method(name, ..) => {
 847                 err.help(&format!("consider moving `{}` to another trait", name));
 848             }
 849         }
 850     }
 851
 852     pub fn spans(&self) -> SmallVec<[Span; 1]> {
 853         // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
 854         // diagnostics use a `note` instead of a `span_label`.
 855         match self {
 856             ObjectSafetyViolation::SupertraitSelf(spans)
 857             | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
 858             ObjectSafetyViolation::AssocConst(_, span)
 859             | ObjectSafetyViolation::GAT(_, span)
 860             | ObjectSafetyViolation::Method(_, _, span)
 861                 if *span != DUMMY_SP =>
 862             {
 863                 smallvec![*span]
 864             }
 865             _ => smallvec![],
 866         }
 867     }
 868 }
 869
 870 /// Reasons a method might not be object-safe.
 871 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 872 pub enum MethodViolationCode {
 873     /// e.g., `fn foo()`
 874     StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),
 875
 876     /// e.g., `fn foo(&self, x: Self)`
 877     ReferencesSelfInput(usize),
 878
 879     /// e.g., `fn foo(&self) -> Self`
 880     ReferencesSelfOutput,
 881
 882     /// e.g., `fn foo(&self) where Self: Clone`
 883     WhereClauseReferencesSelf,
 884
 885     /// e.g., `fn foo<A>()`
 886     Generic,
 887
 888     /// the method's receiver (`self` argument) can't be dispatched on
 889     UndispatchableReceiver,
 890 }