1 //! Trait Resolution. See the [rustc dev guide] for more information on how this works.
3 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
8 pub mod specialization_graph;
12 use crate::infer::canonical::Canonical;
13 use crate::mir::ConstraintCategory;
14 use crate::ty::abstract_const::NotConstEvaluatable;
15 use crate::ty::subst::SubstsRef;
16 use crate::ty::{self, AdtKind, Ty, TyCtxt};
18 use rustc_data_structures::sync::Lrc;
19 use rustc_errors::{Applicability, Diagnostic};
21 use rustc_hir::def_id::{DefId, LocalDefId};
22 use rustc_span::symbol::Symbol;
23 use rustc_span::{Span, DUMMY_SP};
24 use smallvec::SmallVec;
27 use std::hash::{Hash, Hasher};
29 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
31 pub type CanonicalChalkEnvironmentAndGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>;
33 pub use self::ObligationCauseCode::*;
35 pub use self::chalk::{ChalkEnvironmentAndGoal, RustInterner as ChalkRustInterner};
37 /// Depending on the stage of compilation, we want projection to be
38 /// more or less conservative.
39 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
41 /// At type-checking time, we refuse to project any associated
42 /// type that is marked `default`. Non-`default` ("final") types
43 /// are always projected. This is necessary in general for
44 /// soundness of specialization. However, we *could* allow
45 /// projections in fully-monomorphic cases. We choose not to,
46 /// because we prefer for `default type` to force the type
47 /// definition to be treated abstractly by any consumers of the
48 /// impl. Concretely, that means that the following example will
51 /// ```compile_fail,E0308
52 /// #![feature(specialization)]
57 /// impl<T> Assoc for T {
58 /// default type Output = bool;
62 /// let x: <() as Assoc>::Output = true;
66 /// We also do not reveal the hidden type of opaque types during
70 /// At codegen time, all monomorphic projections will succeed.
71 /// Also, `impl Trait` is normalized to the concrete type,
72 /// which has to be already collected by type-checking.
74 /// NOTE: as `impl Trait`'s concrete type should *never*
75 /// be observable directly by the user, `Reveal::All`
76 /// should not be used by checks which may expose
77 /// type equality or type contents to the user.
78 /// There are some exceptions, e.g., around auto traits and
79 /// transmute-checking, which expose some details, but
80 /// not the whole concrete type of the `impl Trait`.
84 /// The reason why we incurred this obligation; used for error reporting.
86 /// Non-misc `ObligationCauseCode`s are stored on the heap. This gives the
87 /// best trade-off between keeping the type small (which makes copies cheaper)
88 /// while not doing too many heap allocations.
90 /// We do not want to intern this as there are a lot of obligation causes which
91 /// only live for a short period of time.
92 #[derive(Clone, Debug, PartialEq, Eq, Lift)]
93 pub struct ObligationCause<'tcx> {
96 /// The ID of the fn body that triggered this obligation. This is
97 /// used for region obligations to determine the precise
98 /// environment in which the region obligation should be evaluated
99 /// (in particular, closures can add new assumptions). See the
100 /// field `region_obligations` of the `FulfillmentContext` for more
102 pub body_id: hir::HirId,
104 code: InternedObligationCauseCode<'tcx>,
107 // This custom hash function speeds up hashing for `Obligation` deduplication
108 // greatly by skipping the `code` field, which can be large and complex. That
109 // shouldn't affect hash quality much since there are several other fields in
110 // `Obligation` which should be unique enough, especially the predicate itself
111 // which is hashed as an interned pointer. See #90996.
112 impl Hash for ObligationCause<'_> {
113 fn hash<H: Hasher>(&self, state: &mut H) {
114 self.body_id.hash(state);
115 self.span.hash(state);
119 impl<'tcx> ObligationCause<'tcx> {
124 code: ObligationCauseCode<'tcx>,
125 ) -> ObligationCause<'tcx> {
126 ObligationCause { span, body_id, code: code.into() }
129 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
130 ObligationCause::new(span, body_id, MiscObligation)
134 pub fn dummy() -> ObligationCause<'tcx> {
135 ObligationCause::dummy_with_span(DUMMY_SP)
139 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
140 ObligationCause { span, body_id: hir::CRATE_HIR_ID, code: Default::default() }
143 pub fn span(&self) -> Span {
145 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
154 pub fn code(&self) -> &ObligationCauseCode<'tcx> {
160 f: impl FnOnce(InternedObligationCauseCode<'tcx>) -> ObligationCauseCode<'tcx>,
162 self.code = f(std::mem::take(&mut self.code)).into();
165 pub fn derived_cause(
167 parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
168 variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,
169 ) -> ObligationCause<'tcx> {
171 * Creates a cause for obligations that are derived from
172 * `obligation` by a recursive search (e.g., for a builtin
173 * bound, or eventually a `auto trait Foo`). If `obligation`
174 * is itself a derived obligation, this is just a clone, but
175 * otherwise we create a "derived obligation" cause so as to
176 * keep track of the original root obligation for error
180 // NOTE(flaper87): As of now, it keeps track of the whole error
181 // chain. Ideally, we should have a way to configure this either
182 // by using -Z verbose or just a CLI argument.
184 variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into();
188 pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
190 MatchImpl(cause, _) => cause.to_constraint_category(),
191 AscribeUserTypeProvePredicate(predicate_span) => {
192 ConstraintCategory::Predicate(*predicate_span)
194 _ => ConstraintCategory::BoringNoLocation,
199 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
200 pub struct UnifyReceiverContext<'tcx> {
201 pub assoc_item: ty::AssocItem,
202 pub param_env: ty::ParamEnv<'tcx>,
203 pub substs: SubstsRef<'tcx>,
206 #[derive(Clone, PartialEq, Eq, Hash, Lift, Default)]
207 pub struct InternedObligationCauseCode<'tcx> {
208 /// `None` for `ObligationCauseCode::MiscObligation` (a common case, occurs ~60% of
209 /// the time). `Some` otherwise.
210 code: Option<Lrc<ObligationCauseCode<'tcx>>>,
213 impl<'tcx> std::fmt::Debug for InternedObligationCauseCode<'tcx> {
214 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
215 let cause: &ObligationCauseCode<'_> = self;
220 impl<'tcx> ObligationCauseCode<'tcx> {
222 fn into(self) -> InternedObligationCauseCode<'tcx> {
223 InternedObligationCauseCode {
224 code: if let ObligationCauseCode::MiscObligation = self {
233 impl<'tcx> std::ops::Deref for InternedObligationCauseCode<'tcx> {
234 type Target = ObligationCauseCode<'tcx>;
236 fn deref(&self) -> &Self::Target {
237 self.code.as_deref().unwrap_or(&ObligationCauseCode::MiscObligation)
241 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
242 pub enum ObligationCauseCode<'tcx> {
243 /// Not well classified or should be obvious from the span.
246 /// A slice or array is WF only if `T: Sized`.
249 /// A tuple is WF only if its middle elements are `Sized`.
252 /// This is the trait reference from the given projection.
253 ProjectionWf(ty::ProjectionTy<'tcx>),
255 /// Must satisfy all of the where-clause predicates of the
257 ItemObligation(DefId),
259 /// Like `ItemObligation`, but carries the span of the
260 /// predicate when it can be identified.
261 BindingObligation(DefId, Span),
263 /// Like `ItemObligation`, but carries the `HirId` of the
264 /// expression that caused the obligation, and the `usize`
265 /// indicates exactly which predicate it is in the list of
266 /// instantiated predicates.
267 ExprItemObligation(DefId, rustc_hir::HirId, usize),
269 /// Combines `ExprItemObligation` and `BindingObligation`.
270 ExprBindingObligation(DefId, Span, rustc_hir::HirId, usize),
272 /// A type like `&'a T` is WF only if `T: 'a`.
273 ReferenceOutlivesReferent(Ty<'tcx>),
275 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
276 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
278 /// Obligation incurred due to an object cast.
279 ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'tcx>),
281 /// Obligation incurred due to a coercion.
287 /// Various cases where expressions must be `Sized` / `Copy` / etc.
288 /// `L = X` implies that `L` is `Sized`.
290 /// `(x1, .., xn)` must be `Sized`.
291 TupleInitializerSized,
292 /// `S { ... }` must be `Sized`.
293 StructInitializerSized,
294 /// Type of each variable must be `Sized`.
295 VariableType(hir::HirId),
296 /// Argument type must be `Sized`.
297 SizedArgumentType(Option<Span>),
298 /// Return type must be `Sized`.
300 /// Yield type must be `Sized`.
302 /// Box expression result type must be `Sized`.
304 /// Inline asm operand type must be `Sized`.
306 /// `[expr; N]` requires `type_of(expr): Copy`.
308 /// If element is a `const fn` we display a help message suggesting to move the
309 /// function call to a new `const` item while saying that `T` doesn't implement `Copy`.
313 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
320 /// Constant expressions must be sized.
323 /// `static` items must have `Sync` type.
326 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
328 ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>),
330 DerivedObligation(DerivedObligationCause<'tcx>),
332 FunctionArgumentObligation {
333 /// The node of the relevant argument in the function call.
334 arg_hir_id: hir::HirId,
335 /// The node of the function call.
336 call_hir_id: hir::HirId,
337 /// The obligation introduced by this argument.
338 parent_code: InternedObligationCauseCode<'tcx>,
341 /// Error derived when matching traits/impls; see ObligationCause for more details
342 CompareImplItemObligation {
343 impl_item_def_id: LocalDefId,
344 trait_item_def_id: DefId,
348 /// Checking that the bounds of a trait's associated type hold for a given impl
349 CheckAssociatedTypeBounds {
350 impl_item_def_id: LocalDefId,
351 trait_item_def_id: DefId,
354 /// Checking that this expression can be assigned to its target.
357 /// Computing common supertype in the arms of a match expression
358 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
360 /// Type error arising from type checking a pattern against an expected type.
362 /// The span of the scrutinee or type expression which caused the `root_ty` type.
364 /// The root expected type induced by a scrutinee or type expression.
366 /// Whether the `Span` came from an expression or a type expression.
370 /// Constants in patterns must have `Structural` type.
371 ConstPatternStructural,
373 /// Computing common supertype in an if expression
374 IfExpression(Box<IfExpressionCause<'tcx>>),
376 /// Computing common supertype of an if expression with no else counter-part
377 IfExpressionWithNoElse,
379 /// `main` has wrong type
382 /// `start` has wrong type
385 /// Intrinsic has wrong type
388 /// A let else block does not diverge
394 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
396 /// `return` with no expression
399 /// `return` with an expression
400 ReturnValue(hir::HirId),
402 /// Return type of this function
405 /// Opaque return type of this function
406 OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
408 /// Block implicit return
409 BlockTailExpression(hir::HirId),
411 /// #[feature(trivial_bounds)] is not enabled
414 /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
417 AwaitableExpr(Option<hir::HirId>),
423 /// Well-formed checking. If a `WellFormedLoc` is provided,
424 /// then it will be used to perform HIR-based wf checking
425 /// after an error occurs, in order to generate a more precise error span.
426 /// This is purely for diagnostic purposes - it is always
427 /// correct to use `MiscObligation` instead, or to specify
428 /// `WellFormed(None)`
429 WellFormed(Option<WellFormedLoc>),
431 /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
432 MatchImpl(ObligationCause<'tcx>, DefId),
435 rhs_span: Option<Span>,
437 output_ty: Option<Ty<'tcx>>,
440 AscribeUserTypeProvePredicate(Span),
445 /// The 'location' at which we try to perform HIR-based wf checking.
446 /// This information is used to obtain an `hir::Ty`, which
447 /// we can walk in order to obtain precise spans for any
448 /// 'nested' types (e.g. `Foo` in `Option<Foo>`).
449 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
450 pub enum WellFormedLoc {
451 /// Use the type of the provided definition.
453 /// Use the type of the parameter of the provided function.
454 /// We cannot use `hir::Param`, since the function may
455 /// not have a body (e.g. a trait method definition)
457 /// The function to lookup the parameter in
458 function: LocalDefId,
459 /// The index of the parameter to use.
460 /// Parameters are indexed from 0, with the return type
461 /// being the last 'parameter'
466 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
467 pub struct ImplDerivedObligationCause<'tcx> {
468 pub derived: DerivedObligationCause<'tcx>,
469 pub impl_def_id: DefId,
473 impl<'tcx> ObligationCauseCode<'tcx> {
474 // Return the base obligation, ignoring derived obligations.
475 pub fn peel_derives(&self) -> &Self {
476 let mut base_cause = self;
477 while let Some((parent_code, _)) = base_cause.parent() {
478 base_cause = parent_code;
483 pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> {
485 FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)),
486 BuiltinDerivedObligation(derived)
487 | DerivedObligation(derived)
488 | ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => {
489 Some((&derived.parent_code, Some(derived.parent_trait_pred)))
495 pub fn peel_match_impls(&self) -> &Self {
497 MatchImpl(cause, _) => cause.code(),
503 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
504 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
505 static_assert_size!(ObligationCauseCode<'_>, 48);
507 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
508 pub enum StatementAsExpression {
513 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
514 type Lifted = StatementAsExpression;
515 fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
520 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
521 pub struct MatchExpressionArmCause<'tcx> {
522 pub arm_block_id: Option<hir::HirId>,
523 pub arm_ty: Ty<'tcx>,
525 pub prior_arm_block_id: Option<hir::HirId>,
526 pub prior_arm_ty: Ty<'tcx>,
527 pub prior_arm_span: Span,
528 pub scrut_span: Span,
529 pub source: hir::MatchSource,
530 pub prior_arms: Vec<Span>,
531 pub scrut_hir_id: hir::HirId,
532 pub opt_suggest_box_span: Option<Span>,
535 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
536 #[derive(Lift, TypeFoldable, TypeVisitable)]
537 pub struct IfExpressionCause<'tcx> {
538 pub then_id: hir::HirId,
539 pub else_id: hir::HirId,
540 pub then_ty: Ty<'tcx>,
541 pub else_ty: Ty<'tcx>,
542 pub outer_span: Option<Span>,
543 pub opt_suggest_box_span: Option<Span>,
546 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
547 pub struct DerivedObligationCause<'tcx> {
548 /// The trait predicate of the parent obligation that led to the
549 /// current obligation. Note that only trait obligations lead to
550 /// derived obligations, so we just store the trait predicate here
552 pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
554 /// The parent trait had this cause.
555 pub parent_code: InternedObligationCauseCode<'tcx>,
558 #[derive(Clone, Debug, TypeFoldable, TypeVisitable, Lift)]
559 pub enum SelectionError<'tcx> {
560 /// The trait is not implemented.
562 /// After a closure impl has selected, its "outputs" were evaluated
563 /// (which for closures includes the "input" type params) and they
564 /// didn't resolve. See `confirm_poly_trait_refs` for more.
565 OutputTypeParameterMismatch(
566 ty::PolyTraitRef<'tcx>,
567 ty::PolyTraitRef<'tcx>,
568 ty::error::TypeError<'tcx>,
570 /// The trait pointed by `DefId` is not object safe.
571 TraitNotObjectSafe(DefId),
572 /// A given constant couldn't be evaluated.
573 NotConstEvaluatable(NotConstEvaluatable),
574 /// Exceeded the recursion depth during type projection.
575 Overflow(OverflowError),
576 /// Signaling that an error has already been emitted, to avoid
577 /// multiple errors being shown.
581 /// When performing resolution, it is typically the case that there
582 /// can be one of three outcomes:
584 /// - `Ok(Some(r))`: success occurred with result `r`
585 /// - `Ok(None)`: could not definitely determine anything, usually due
586 /// to inconclusive type inference.
587 /// - `Err(e)`: error `e` occurred
588 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
590 /// Given the successful resolution of an obligation, the `ImplSource`
591 /// indicates where the impl comes from.
593 /// For example, the obligation may be satisfied by a specific impl (case A),
594 /// or it may be relative to some bound that is in scope (case B).
596 /// ```ignore (illustrative)
597 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
598 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
599 /// impl Clone for i32 { ... } // Impl_3
601 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
602 /// // Case A: ImplSource points at a specific impl. Only possible when
603 /// // type is concretely known. If the impl itself has bounded
604 /// // type parameters, ImplSource will carry resolutions for those as well:
605 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
607 /// // Case B: ImplSource must be provided by caller. This applies when
608 /// // type is a type parameter.
609 /// param.clone(); // ImplSource::Param
611 /// // Case C: A mix of cases A and B.
612 /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param])
616 /// ### The type parameter `N`
618 /// See explanation on `ImplSourceUserDefinedData`.
619 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
620 #[derive(TypeFoldable, TypeVisitable)]
621 pub enum ImplSource<'tcx, N> {
622 /// ImplSource identifying a particular impl.
623 UserDefined(ImplSourceUserDefinedData<'tcx, N>),
625 /// ImplSource for auto trait implementations.
626 /// This carries the information and nested obligations with regards
627 /// to an auto implementation for a trait `Trait`. The nested obligations
628 /// ensure the trait implementation holds for all the constituent types.
629 AutoImpl(ImplSourceAutoImplData<N>),
631 /// Successful resolution to an obligation provided by the caller
632 /// for some type parameter. The `Vec<N>` represents the
633 /// obligations incurred from normalizing the where-clause (if
635 Param(Vec<N>, ty::BoundConstness),
637 /// Virtual calls through an object.
638 Object(ImplSourceObjectData<'tcx, N>),
640 /// Successful resolution for a builtin trait.
641 Builtin(ImplSourceBuiltinData<N>),
643 /// ImplSource for trait upcasting coercion
644 TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
646 /// ImplSource automatically generated for a closure. The `DefId` is the ID
647 /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the
648 /// impl is generated by the compiler and does not appear in the source.
649 Closure(ImplSourceClosureData<'tcx, N>),
651 /// Same as above, but for a function pointer type with the given signature.
652 FnPointer(ImplSourceFnPointerData<'tcx, N>),
654 /// ImplSource for a builtin `DeterminantKind` trait implementation.
655 DiscriminantKind(ImplSourceDiscriminantKindData),
657 /// ImplSource for a builtin `Pointee` trait implementation.
658 Pointee(ImplSourcePointeeData),
660 /// ImplSource automatically generated for a generator.
661 Generator(ImplSourceGeneratorData<'tcx, N>),
663 /// ImplSource for a trait alias.
664 TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
666 /// ImplSource for a `const Drop` implementation.
667 ConstDestruct(ImplSourceConstDestructData<N>),
670 impl<'tcx, N> ImplSource<'tcx, N> {
671 pub fn nested_obligations(self) -> Vec<N> {
673 ImplSource::UserDefined(i) => i.nested,
674 ImplSource::Param(n, _) => n,
675 ImplSource::Builtin(i) => i.nested,
676 ImplSource::AutoImpl(d) => d.nested,
677 ImplSource::Closure(c) => c.nested,
678 ImplSource::Generator(c) => c.nested,
679 ImplSource::Object(d) => d.nested,
680 ImplSource::FnPointer(d) => d.nested,
681 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
682 | ImplSource::Pointee(ImplSourcePointeeData) => vec![],
683 ImplSource::TraitAlias(d) => d.nested,
684 ImplSource::TraitUpcasting(d) => d.nested,
685 ImplSource::ConstDestruct(i) => i.nested,
689 pub fn borrow_nested_obligations(&self) -> &[N] {
691 ImplSource::UserDefined(i) => &i.nested[..],
692 ImplSource::Param(n, _) => &n,
693 ImplSource::Builtin(i) => &i.nested,
694 ImplSource::AutoImpl(d) => &d.nested,
695 ImplSource::Closure(c) => &c.nested,
696 ImplSource::Generator(c) => &c.nested,
697 ImplSource::Object(d) => &d.nested,
698 ImplSource::FnPointer(d) => &d.nested,
699 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
700 | ImplSource::Pointee(ImplSourcePointeeData) => &[],
701 ImplSource::TraitAlias(d) => &d.nested,
702 ImplSource::TraitUpcasting(d) => &d.nested,
703 ImplSource::ConstDestruct(i) => &i.nested,
707 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
712 ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
713 impl_def_id: i.impl_def_id,
715 nested: i.nested.into_iter().map(f).collect(),
717 ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
718 ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
719 nested: i.nested.into_iter().map(f).collect(),
721 ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
722 upcast_trait_ref: o.upcast_trait_ref,
723 vtable_base: o.vtable_base,
724 nested: o.nested.into_iter().map(f).collect(),
726 ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
727 trait_def_id: d.trait_def_id,
728 nested: d.nested.into_iter().map(f).collect(),
730 ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
731 closure_def_id: c.closure_def_id,
733 nested: c.nested.into_iter().map(f).collect(),
735 ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
736 generator_def_id: c.generator_def_id,
738 nested: c.nested.into_iter().map(f).collect(),
740 ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
742 nested: p.nested.into_iter().map(f).collect(),
744 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
745 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
747 ImplSource::Pointee(ImplSourcePointeeData) => {
748 ImplSource::Pointee(ImplSourcePointeeData)
750 ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
751 alias_def_id: d.alias_def_id,
753 nested: d.nested.into_iter().map(f).collect(),
755 ImplSource::TraitUpcasting(d) => {
756 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
757 upcast_trait_ref: d.upcast_trait_ref,
758 vtable_vptr_slot: d.vtable_vptr_slot,
759 nested: d.nested.into_iter().map(f).collect(),
762 ImplSource::ConstDestruct(i) => {
763 ImplSource::ConstDestruct(ImplSourceConstDestructData {
764 nested: i.nested.into_iter().map(f).collect(),
771 /// Identifies a particular impl in the source, along with a set of
772 /// substitutions from the impl's type/lifetime parameters. The
773 /// `nested` vector corresponds to the nested obligations attached to
774 /// the impl's type parameters.
776 /// The type parameter `N` indicates the type used for "nested
777 /// obligations" that are required by the impl. During type-check, this
778 /// is `Obligation`, as one might expect. During codegen, however, this
779 /// is `()`, because codegen only requires a shallow resolution of an
780 /// impl, and nested obligations are satisfied later.
781 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
782 #[derive(TypeFoldable, TypeVisitable)]
783 pub struct ImplSourceUserDefinedData<'tcx, N> {
784 pub impl_def_id: DefId,
785 pub substs: SubstsRef<'tcx>,
789 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
790 #[derive(TypeFoldable, TypeVisitable)]
791 pub struct ImplSourceGeneratorData<'tcx, N> {
792 pub generator_def_id: DefId,
793 pub substs: SubstsRef<'tcx>,
794 /// Nested obligations. This can be non-empty if the generator
795 /// signature contains associated types.
799 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
800 #[derive(TypeFoldable, TypeVisitable)]
801 pub struct ImplSourceClosureData<'tcx, N> {
802 pub closure_def_id: DefId,
803 pub substs: SubstsRef<'tcx>,
804 /// Nested obligations. This can be non-empty if the closure
805 /// signature contains associated types.
809 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
810 #[derive(TypeFoldable, TypeVisitable)]
811 pub struct ImplSourceAutoImplData<N> {
812 pub trait_def_id: DefId,
816 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
817 #[derive(TypeFoldable, TypeVisitable)]
818 pub struct ImplSourceTraitUpcastingData<'tcx, N> {
819 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
820 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
822 /// The vtable is formed by concatenating together the method lists of
823 /// the base object trait and all supertraits, pointers to supertrait vtable will
824 /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
825 /// within that vtable.
826 pub vtable_vptr_slot: Option<usize>,
831 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
832 #[derive(TypeFoldable, TypeVisitable)]
833 pub struct ImplSourceBuiltinData<N> {
837 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, Lift)]
838 #[derive(TypeFoldable, TypeVisitable)]
839 pub struct ImplSourceObjectData<'tcx, N> {
840 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
841 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
843 /// The vtable is formed by concatenating together the method lists of
844 /// the base object trait and all supertraits, pointers to supertrait vtable will
845 /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
847 pub vtable_base: usize,
852 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
853 #[derive(TypeFoldable, TypeVisitable)]
854 pub struct ImplSourceFnPointerData<'tcx, N> {
859 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
860 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
861 pub struct ImplSourceDiscriminantKindData;
863 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
864 pub struct ImplSourcePointeeData;
866 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
867 #[derive(TypeFoldable, TypeVisitable)]
868 pub struct ImplSourceConstDestructData<N> {
872 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
873 #[derive(TypeFoldable, TypeVisitable)]
874 pub struct ImplSourceTraitAliasData<'tcx, N> {
875 pub alias_def_id: DefId,
876 pub substs: SubstsRef<'tcx>,
880 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
881 pub enum ObjectSafetyViolation {
882 /// `Self: Sized` declared on the trait.
883 SizedSelf(SmallVec<[Span; 1]>),
885 /// Supertrait reference references `Self` an in illegal location
886 /// (e.g., `trait Foo : Bar<Self>`).
887 SupertraitSelf(SmallVec<[Span; 1]>),
889 /// Method has something illegal.
890 Method(Symbol, MethodViolationCode, Span),
892 /// Associated const.
893 AssocConst(Symbol, Span),
899 impl ObjectSafetyViolation {
900 pub fn error_msg(&self) -> Cow<'static, str> {
902 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
903 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
904 if spans.iter().any(|sp| *sp != DUMMY_SP) {
905 "it uses `Self` as a type parameter".into()
907 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
911 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
912 format!("associated function `{}` has no `self` parameter", name).into()
914 ObjectSafetyViolation::Method(
916 MethodViolationCode::ReferencesSelfInput(_),
918 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
919 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
920 format!("method `{}` references the `Self` type in this parameter", name).into()
922 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
923 format!("method `{}` references the `Self` type in its return type", name).into()
925 ObjectSafetyViolation::Method(
927 MethodViolationCode::ReferencesImplTraitInTrait(_),
929 ) => format!("method `{}` references an `impl Trait` type in its return type", name)
931 ObjectSafetyViolation::Method(name, MethodViolationCode::AsyncFn, _) => {
932 format!("method `{}` is `async`", name).into()
934 ObjectSafetyViolation::Method(
936 MethodViolationCode::WhereClauseReferencesSelf,
939 format!("method `{}` references the `Self` type in its `where` clause", name).into()
941 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
942 format!("method `{}` has generic type parameters", name).into()
944 ObjectSafetyViolation::Method(
946 MethodViolationCode::UndispatchableReceiver(_),
948 ) => format!("method `{}`'s `self` parameter cannot be dispatched on", name).into(),
949 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
950 format!("it contains associated `const` `{}`", name).into()
952 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
953 ObjectSafetyViolation::GAT(name, _) => {
954 format!("it contains the generic associated type `{}`", name).into()
959 pub fn solution(&self, err: &mut Diagnostic) {
961 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
962 ObjectSafetyViolation::Method(
964 MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))),
970 "consider turning `{}` into a method by giving it a `&self` argument",
973 add_self_sugg.0.to_string(),
974 Applicability::MaybeIncorrect,
979 "alternatively, consider constraining `{}` so it does not apply to \
983 make_sized_sugg.0.to_string(),
984 Applicability::MaybeIncorrect,
987 ObjectSafetyViolation::Method(
989 MethodViolationCode::UndispatchableReceiver(Some(span)),
995 "consider changing method `{}`'s `self` parameter to be `&self`",
999 Applicability::MachineApplicable,
1002 ObjectSafetyViolation::AssocConst(name, _)
1003 | ObjectSafetyViolation::GAT(name, _)
1004 | ObjectSafetyViolation::Method(name, ..) => {
1005 err.help(&format!("consider moving `{}` to another trait", name));
1010 pub fn spans(&self) -> SmallVec<[Span; 1]> {
1011 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
1012 // diagnostics use a `note` instead of a `span_label`.
1014 ObjectSafetyViolation::SupertraitSelf(spans)
1015 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
1016 ObjectSafetyViolation::AssocConst(_, span)
1017 | ObjectSafetyViolation::GAT(_, span)
1018 | ObjectSafetyViolation::Method(_, _, span)
1019 if *span != DUMMY_SP =>
1028 /// Reasons a method might not be object-safe.
1029 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
1030 pub enum MethodViolationCode {
1031 /// e.g., `fn foo()`
1032 StaticMethod(Option<(/* add &self */ (String, Span), /* add Self: Sized */ (String, Span))>),
1034 /// e.g., `fn foo(&self, x: Self)`
1035 ReferencesSelfInput(Option<Span>),
1037 /// e.g., `fn foo(&self) -> Self`
1038 ReferencesSelfOutput,
1040 /// e.g., `fn foo(&self) -> impl Sized`
1041 ReferencesImplTraitInTrait(Span),
1043 /// e.g., `async fn foo(&self)`
1046 /// e.g., `fn foo(&self) where Self: Clone`
1047 WhereClauseReferencesSelf,
1049 /// e.g., `fn foo<A>()`
1052 /// the method's receiver (`self` argument) can't be dispatched on
1053 UndispatchableReceiver(Option<Span>),
1056 /// These are the error cases for `codegen_select_candidate`.
1057 #[derive(Copy, Clone, Debug, Hash, HashStable, Encodable, Decodable)]
1058 pub enum CodegenObligationError {
1059 /// Ambiguity can happen when monomorphizing during trans
1060 /// expands to some humongous type that never occurred
1061 /// statically -- this humongous type can then overflow,
1062 /// leading to an ambiguous result. So report this as an
1063 /// overflow bug, since I believe this is the only case
1064 /// where ambiguity can result.
1066 /// This can trigger when we probe for the source of a `'static` lifetime requirement
1067 /// on a trait object: `impl Foo for dyn Trait {}` has an implicit `'static` bound.
1068 /// This can also trigger when we have a global bound that is not actually satisfied,
1069 /// but was included during typeck due to the trivial_bounds feature.