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, Debug, 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> ObligationCauseCode<'tcx> {
215 fn into(self) -> InternedObligationCauseCode<'tcx> {
216 InternedObligationCauseCode {
217 code: if let ObligationCauseCode::MiscObligation = self {
226 impl<'tcx> std::ops::Deref for InternedObligationCauseCode<'tcx> {
227 type Target = ObligationCauseCode<'tcx>;
229 fn deref(&self) -> &Self::Target {
230 self.code.as_deref().unwrap_or(&ObligationCauseCode::MiscObligation)
234 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
235 pub enum ObligationCauseCode<'tcx> {
236 /// Not well classified or should be obvious from the span.
239 /// A slice or array is WF only if `T: Sized`.
242 /// A tuple is WF only if its middle elements are `Sized`.
245 /// This is the trait reference from the given projection.
246 ProjectionWf(ty::ProjectionTy<'tcx>),
248 /// Must satisfy all of the where-clause predicates of the
250 ItemObligation(DefId),
252 /// Like `ItemObligation`, but carries the span of the
253 /// predicate when it can be identified.
254 BindingObligation(DefId, Span),
256 /// Like `ItemObligation`, but carries the `HirId` of the
257 /// expression that caused the obligation, and the `usize`
258 /// indicates exactly which predicate it is in the list of
259 /// instantiated predicates.
260 ExprItemObligation(DefId, rustc_hir::HirId, usize),
262 /// Combines `ExprItemObligation` and `BindingObligation`.
263 ExprBindingObligation(DefId, Span, rustc_hir::HirId, usize),
265 /// A type like `&'a T` is WF only if `T: 'a`.
266 ReferenceOutlivesReferent(Ty<'tcx>),
268 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
269 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
271 /// Obligation incurred due to an object cast.
272 ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'tcx>),
274 /// Obligation incurred due to a coercion.
280 /// Various cases where expressions must be `Sized` / `Copy` / etc.
281 /// `L = X` implies that `L` is `Sized`.
283 /// `(x1, .., xn)` must be `Sized`.
284 TupleInitializerSized,
285 /// `S { ... }` must be `Sized`.
286 StructInitializerSized,
287 /// Type of each variable must be `Sized`.
288 VariableType(hir::HirId),
289 /// Argument type must be `Sized`.
290 SizedArgumentType(Option<Span>),
291 /// Return type must be `Sized`.
293 /// Yield type must be `Sized`.
295 /// Box expression result type must be `Sized`.
297 /// Inline asm operand type must be `Sized`.
299 /// `[expr; N]` requires `type_of(expr): Copy`.
301 /// If element is a `const fn` we display a help message suggesting to move the
302 /// function call to a new `const` item while saying that `T` doesn't implement `Copy`.
306 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
313 /// Constant expressions must be sized.
316 /// `static` items must have `Sync` type.
319 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
321 ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>),
323 DerivedObligation(DerivedObligationCause<'tcx>),
325 FunctionArgumentObligation {
326 /// The node of the relevant argument in the function call.
327 arg_hir_id: hir::HirId,
328 /// The node of the function call.
329 call_hir_id: hir::HirId,
330 /// The obligation introduced by this argument.
331 parent_code: InternedObligationCauseCode<'tcx>,
334 /// Error derived when matching traits/impls; see ObligationCause for more details
335 CompareImplItemObligation {
336 impl_item_def_id: LocalDefId,
337 trait_item_def_id: DefId,
341 /// Checking that the bounds of a trait's associated type hold for a given impl
342 CheckAssociatedTypeBounds {
343 impl_item_def_id: LocalDefId,
344 trait_item_def_id: DefId,
347 /// Checking that this expression can be assigned to its target.
350 /// Computing common supertype in the arms of a match expression
351 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
353 /// Type error arising from type checking a pattern against an expected type.
355 /// The span of the scrutinee or type expression which caused the `root_ty` type.
357 /// The root expected type induced by a scrutinee or type expression.
359 /// Whether the `Span` came from an expression or a type expression.
363 /// Constants in patterns must have `Structural` type.
364 ConstPatternStructural,
366 /// Computing common supertype in an if expression
367 IfExpression(Box<IfExpressionCause<'tcx>>),
369 /// Computing common supertype of an if expression with no else counter-part
370 IfExpressionWithNoElse,
372 /// `main` has wrong type
375 /// `start` has wrong type
378 /// Intrinsic has wrong type
381 /// A let else block does not diverge
387 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
389 /// `return` with no expression
392 /// `return` with an expression
393 ReturnValue(hir::HirId),
395 /// Return type of this function
398 /// Opaque return type of this function
399 OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
401 /// Block implicit return
402 BlockTailExpression(hir::HirId),
404 /// #[feature(trivial_bounds)] is not enabled
407 /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
410 AwaitableExpr(Option<hir::HirId>),
416 /// Well-formed checking. If a `WellFormedLoc` is provided,
417 /// then it will be used to perform HIR-based wf checking
418 /// after an error occurs, in order to generate a more precise error span.
419 /// This is purely for diagnostic purposes - it is always
420 /// correct to use `MiscObligation` instead, or to specify
421 /// `WellFormed(None)`
422 WellFormed(Option<WellFormedLoc>),
424 /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
425 MatchImpl(ObligationCause<'tcx>, DefId),
428 rhs_span: Option<Span>,
430 output_ty: Option<Ty<'tcx>>,
433 AscribeUserTypeProvePredicate(Span),
436 /// The 'location' at which we try to perform HIR-based wf checking.
437 /// This information is used to obtain an `hir::Ty`, which
438 /// we can walk in order to obtain precise spans for any
439 /// 'nested' types (e.g. `Foo` in `Option<Foo>`).
440 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
441 pub enum WellFormedLoc {
442 /// Use the type of the provided definition.
444 /// Use the type of the parameter of the provided function.
445 /// We cannot use `hir::Param`, since the function may
446 /// not have a body (e.g. a trait method definition)
448 /// The function to lookup the parameter in
449 function: LocalDefId,
450 /// The index of the parameter to use.
451 /// Parameters are indexed from 0, with the return type
452 /// being the last 'parameter'
457 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
458 pub struct ImplDerivedObligationCause<'tcx> {
459 pub derived: DerivedObligationCause<'tcx>,
460 pub impl_def_id: DefId,
464 impl<'tcx> ObligationCauseCode<'tcx> {
465 // Return the base obligation, ignoring derived obligations.
466 pub fn peel_derives(&self) -> &Self {
467 let mut base_cause = self;
468 while let Some((parent_code, _)) = base_cause.parent() {
469 base_cause = parent_code;
474 pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> {
476 FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)),
477 BuiltinDerivedObligation(derived)
478 | DerivedObligation(derived)
479 | ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => {
480 Some((&derived.parent_code, Some(derived.parent_trait_pred)))
486 pub fn peel_match_impls(&self) -> &Self {
488 MatchImpl(cause, _) => cause.code(),
494 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
495 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
496 static_assert_size!(ObligationCauseCode<'_>, 48);
498 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
499 pub enum StatementAsExpression {
504 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
505 type Lifted = StatementAsExpression;
506 fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
511 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
512 pub struct MatchExpressionArmCause<'tcx> {
513 pub arm_block_id: Option<hir::HirId>,
514 pub arm_ty: Ty<'tcx>,
516 pub prior_arm_block_id: Option<hir::HirId>,
517 pub prior_arm_ty: Ty<'tcx>,
518 pub prior_arm_span: Span,
519 pub scrut_span: Span,
520 pub source: hir::MatchSource,
521 pub prior_arms: Vec<Span>,
522 pub scrut_hir_id: hir::HirId,
523 pub opt_suggest_box_span: Option<Span>,
526 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
527 #[derive(Lift, TypeFoldable, TypeVisitable)]
528 pub struct IfExpressionCause<'tcx> {
529 pub then_id: hir::HirId,
530 pub else_id: hir::HirId,
531 pub then_ty: Ty<'tcx>,
532 pub else_ty: Ty<'tcx>,
533 pub outer_span: Option<Span>,
534 pub opt_suggest_box_span: Option<Span>,
537 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
538 pub struct DerivedObligationCause<'tcx> {
539 /// The trait predicate of the parent obligation that led to the
540 /// current obligation. Note that only trait obligations lead to
541 /// derived obligations, so we just store the trait predicate here
543 pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
545 /// The parent trait had this cause.
546 pub parent_code: InternedObligationCauseCode<'tcx>,
549 #[derive(Clone, Debug, TypeFoldable, TypeVisitable, Lift)]
550 pub enum SelectionError<'tcx> {
551 /// The trait is not implemented.
553 /// After a closure impl has selected, its "outputs" were evaluated
554 /// (which for closures includes the "input" type params) and they
555 /// didn't resolve. See `confirm_poly_trait_refs` for more.
556 OutputTypeParameterMismatch(
557 ty::PolyTraitRef<'tcx>,
558 ty::PolyTraitRef<'tcx>,
559 ty::error::TypeError<'tcx>,
561 /// The trait pointed by `DefId` is not object safe.
562 TraitNotObjectSafe(DefId),
563 /// A given constant couldn't be evaluated.
564 NotConstEvaluatable(NotConstEvaluatable),
565 /// Exceeded the recursion depth during type projection.
566 Overflow(OverflowError),
567 /// Signaling that an error has already been emitted, to avoid
568 /// multiple errors being shown.
570 /// Multiple applicable `impl`s where found. The `DefId`s correspond to
571 /// all the `impl`s' Items.
572 Ambiguous(Vec<DefId>),
575 /// When performing resolution, it is typically the case that there
576 /// can be one of three outcomes:
578 /// - `Ok(Some(r))`: success occurred with result `r`
579 /// - `Ok(None)`: could not definitely determine anything, usually due
580 /// to inconclusive type inference.
581 /// - `Err(e)`: error `e` occurred
582 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
584 /// Given the successful resolution of an obligation, the `ImplSource`
585 /// indicates where the impl comes from.
587 /// For example, the obligation may be satisfied by a specific impl (case A),
588 /// or it may be relative to some bound that is in scope (case B).
590 /// ```ignore (illustrative)
591 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
592 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
593 /// impl Clone for i32 { ... } // Impl_3
595 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
596 /// // Case A: ImplSource points at a specific impl. Only possible when
597 /// // type is concretely known. If the impl itself has bounded
598 /// // type parameters, ImplSource will carry resolutions for those as well:
599 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
601 /// // Case A: ImplSource points at a specific impl. Only possible when
602 /// // type is concretely known. If the impl itself has bounded
603 /// // type parameters, ImplSource will carry resolutions for those as well:
604 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
606 /// // Case B: ImplSource must be provided by caller. This applies when
607 /// // type is a type parameter.
608 /// param.clone(); // ImplSource::Param
610 /// // Case C: A mix of cases A and B.
611 /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param])
615 /// ### The type parameter `N`
617 /// See explanation on `ImplSourceUserDefinedData`.
618 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
619 #[derive(TypeFoldable, TypeVisitable)]
620 pub enum ImplSource<'tcx, N> {
621 /// ImplSource identifying a particular impl.
622 UserDefined(ImplSourceUserDefinedData<'tcx, N>),
624 /// ImplSource for auto trait implementations.
625 /// This carries the information and nested obligations with regards
626 /// to an auto implementation for a trait `Trait`. The nested obligations
627 /// ensure the trait implementation holds for all the constituent types.
628 AutoImpl(ImplSourceAutoImplData<N>),
630 /// Successful resolution to an obligation provided by the caller
631 /// for some type parameter. The `Vec<N>` represents the
632 /// obligations incurred from normalizing the where-clause (if
634 Param(Vec<N>, ty::BoundConstness),
636 /// Virtual calls through an object.
637 Object(ImplSourceObjectData<'tcx, N>),
639 /// Successful resolution for a builtin trait.
640 Builtin(ImplSourceBuiltinData<N>),
642 /// ImplSource for trait upcasting coercion
643 TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
645 /// ImplSource automatically generated for a closure. The `DefId` is the ID
646 /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the
647 /// impl is generated by the compiler and does not appear in the source.
648 Closure(ImplSourceClosureData<'tcx, N>),
650 /// Same as above, but for a function pointer type with the given signature.
651 FnPointer(ImplSourceFnPointerData<'tcx, N>),
653 /// ImplSource for a builtin `DeterminantKind` trait implementation.
654 DiscriminantKind(ImplSourceDiscriminantKindData),
656 /// ImplSource for a builtin `Pointee` trait implementation.
657 Pointee(ImplSourcePointeeData),
659 /// ImplSource automatically generated for a generator.
660 Generator(ImplSourceGeneratorData<'tcx, N>),
662 /// ImplSource for a trait alias.
663 TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
665 /// ImplSource for a `const Drop` implementation.
666 ConstDestruct(ImplSourceConstDestructData<N>),
668 /// ImplSource for a `std::marker::Tuple` implementation.
669 /// This has no nested predicates ever, so no data.
673 impl<'tcx, N> ImplSource<'tcx, N> {
674 pub fn nested_obligations(self) -> Vec<N> {
676 ImplSource::UserDefined(i) => i.nested,
677 ImplSource::Param(n, _) => n,
678 ImplSource::Builtin(i) => i.nested,
679 ImplSource::AutoImpl(d) => d.nested,
680 ImplSource::Closure(c) => c.nested,
681 ImplSource::Generator(c) => c.nested,
682 ImplSource::Object(d) => d.nested,
683 ImplSource::FnPointer(d) => d.nested,
684 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
685 | ImplSource::Pointee(ImplSourcePointeeData)
686 | ImplSource::Tuple => Vec::new(),
687 ImplSource::TraitAlias(d) => d.nested,
688 ImplSource::TraitUpcasting(d) => d.nested,
689 ImplSource::ConstDestruct(i) => i.nested,
693 pub fn borrow_nested_obligations(&self) -> &[N] {
695 ImplSource::UserDefined(i) => &i.nested[..],
696 ImplSource::Param(n, _) => &n,
697 ImplSource::Builtin(i) => &i.nested,
698 ImplSource::AutoImpl(d) => &d.nested,
699 ImplSource::Closure(c) => &c.nested,
700 ImplSource::Generator(c) => &c.nested,
701 ImplSource::Object(d) => &d.nested,
702 ImplSource::FnPointer(d) => &d.nested,
703 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
704 | ImplSource::Pointee(ImplSourcePointeeData)
705 | ImplSource::Tuple => &[],
706 ImplSource::TraitAlias(d) => &d.nested,
707 ImplSource::TraitUpcasting(d) => &d.nested,
708 ImplSource::ConstDestruct(i) => &i.nested,
712 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
717 ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
718 impl_def_id: i.impl_def_id,
720 nested: i.nested.into_iter().map(f).collect(),
722 ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
723 ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
724 nested: i.nested.into_iter().map(f).collect(),
726 ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
727 upcast_trait_ref: o.upcast_trait_ref,
728 vtable_base: o.vtable_base,
729 nested: o.nested.into_iter().map(f).collect(),
731 ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
732 trait_def_id: d.trait_def_id,
733 nested: d.nested.into_iter().map(f).collect(),
735 ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
736 closure_def_id: c.closure_def_id,
738 nested: c.nested.into_iter().map(f).collect(),
740 ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
741 generator_def_id: c.generator_def_id,
743 nested: c.nested.into_iter().map(f).collect(),
745 ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
747 nested: p.nested.into_iter().map(f).collect(),
749 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
750 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
752 ImplSource::Pointee(ImplSourcePointeeData) => {
753 ImplSource::Pointee(ImplSourcePointeeData)
755 ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
756 alias_def_id: d.alias_def_id,
758 nested: d.nested.into_iter().map(f).collect(),
760 ImplSource::TraitUpcasting(d) => {
761 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
762 upcast_trait_ref: d.upcast_trait_ref,
763 vtable_vptr_slot: d.vtable_vptr_slot,
764 nested: d.nested.into_iter().map(f).collect(),
767 ImplSource::ConstDestruct(i) => {
768 ImplSource::ConstDestruct(ImplSourceConstDestructData {
769 nested: i.nested.into_iter().map(f).collect(),
772 ImplSource::Tuple => ImplSource::Tuple,
777 /// Identifies a particular impl in the source, along with a set of
778 /// substitutions from the impl's type/lifetime parameters. The
779 /// `nested` vector corresponds to the nested obligations attached to
780 /// the impl's type parameters.
782 /// The type parameter `N` indicates the type used for "nested
783 /// obligations" that are required by the impl. During type-check, this
784 /// is `Obligation`, as one might expect. During codegen, however, this
785 /// is `()`, because codegen only requires a shallow resolution of an
786 /// impl, and nested obligations are satisfied later.
787 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
788 #[derive(TypeFoldable, TypeVisitable)]
789 pub struct ImplSourceUserDefinedData<'tcx, N> {
790 pub impl_def_id: DefId,
791 pub substs: SubstsRef<'tcx>,
795 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
796 #[derive(TypeFoldable, TypeVisitable)]
797 pub struct ImplSourceGeneratorData<'tcx, N> {
798 pub generator_def_id: DefId,
799 pub substs: SubstsRef<'tcx>,
800 /// Nested obligations. This can be non-empty if the generator
801 /// signature contains associated types.
805 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
806 #[derive(TypeFoldable, TypeVisitable)]
807 pub struct ImplSourceClosureData<'tcx, N> {
808 pub closure_def_id: DefId,
809 pub substs: SubstsRef<'tcx>,
810 /// Nested obligations. This can be non-empty if the closure
811 /// signature contains associated types.
815 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
816 #[derive(TypeFoldable, TypeVisitable)]
817 pub struct ImplSourceAutoImplData<N> {
818 pub trait_def_id: DefId,
822 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
823 #[derive(TypeFoldable, TypeVisitable)]
824 pub struct ImplSourceTraitUpcastingData<'tcx, N> {
825 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
826 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
828 /// The vtable is formed by concatenating together the method lists of
829 /// the base object trait and all supertraits, pointers to supertrait vtable will
830 /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
831 /// within that vtable.
832 pub vtable_vptr_slot: Option<usize>,
837 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
838 #[derive(TypeFoldable, TypeVisitable)]
839 pub struct ImplSourceBuiltinData<N> {
843 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, Lift)]
844 #[derive(TypeFoldable, TypeVisitable)]
845 pub struct ImplSourceObjectData<'tcx, N> {
846 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
847 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
849 /// The vtable is formed by concatenating together the method lists of
850 /// the base object trait and all supertraits, pointers to supertrait vtable will
851 /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
853 pub vtable_base: usize,
858 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
859 #[derive(TypeFoldable, TypeVisitable)]
860 pub struct ImplSourceFnPointerData<'tcx, N> {
865 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
866 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
867 pub struct ImplSourceDiscriminantKindData;
869 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
870 pub struct ImplSourcePointeeData;
872 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
873 #[derive(TypeFoldable, TypeVisitable)]
874 pub struct ImplSourceConstDestructData<N> {
878 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)]
879 #[derive(TypeFoldable, TypeVisitable)]
880 pub struct ImplSourceTraitAliasData<'tcx, N> {
881 pub alias_def_id: DefId,
882 pub substs: SubstsRef<'tcx>,
886 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
887 pub enum ObjectSafetyViolation {
888 /// `Self: Sized` declared on the trait.
889 SizedSelf(SmallVec<[Span; 1]>),
891 /// Supertrait reference references `Self` an in illegal location
892 /// (e.g., `trait Foo : Bar<Self>`).
893 SupertraitSelf(SmallVec<[Span; 1]>),
895 /// Method has something illegal.
896 Method(Symbol, MethodViolationCode, Span),
898 /// Associated const.
899 AssocConst(Symbol, Span),
905 impl ObjectSafetyViolation {
906 pub fn error_msg(&self) -> Cow<'static, str> {
908 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
909 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
910 if spans.iter().any(|sp| *sp != DUMMY_SP) {
911 "it uses `Self` as a type parameter".into()
913 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
917 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
918 format!("associated function `{}` has no `self` parameter", name).into()
920 ObjectSafetyViolation::Method(
922 MethodViolationCode::ReferencesSelfInput(_),
924 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
925 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
926 format!("method `{}` references the `Self` type in this parameter", name).into()
928 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
929 format!("method `{}` references the `Self` type in its return type", name).into()
931 ObjectSafetyViolation::Method(
933 MethodViolationCode::ReferencesImplTraitInTrait,
935 ) => format!("method `{}` references an `impl Trait` type in its return type", name)
937 ObjectSafetyViolation::Method(
939 MethodViolationCode::WhereClauseReferencesSelf,
942 format!("method `{}` references the `Self` type in its `where` clause", name).into()
944 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
945 format!("method `{}` has generic type parameters", name).into()
947 ObjectSafetyViolation::Method(
949 MethodViolationCode::UndispatchableReceiver(_),
951 ) => format!("method `{}`'s `self` parameter cannot be dispatched on", name).into(),
952 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
953 format!("it contains associated `const` `{}`", name).into()
955 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
956 ObjectSafetyViolation::GAT(name, _) => {
957 format!("it contains the generic associated type `{}`", name).into()
962 pub fn solution(&self, err: &mut Diagnostic) {
964 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
965 ObjectSafetyViolation::Method(
967 MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))),
973 "consider turning `{}` into a method by giving it a `&self` argument",
976 add_self_sugg.0.to_string(),
977 Applicability::MaybeIncorrect,
982 "alternatively, consider constraining `{}` so it does not apply to \
986 make_sized_sugg.0.to_string(),
987 Applicability::MaybeIncorrect,
990 ObjectSafetyViolation::Method(
992 MethodViolationCode::UndispatchableReceiver(Some(span)),
998 "consider changing method `{}`'s `self` parameter to be `&self`",
1002 Applicability::MachineApplicable,
1005 ObjectSafetyViolation::AssocConst(name, _)
1006 | ObjectSafetyViolation::GAT(name, _)
1007 | ObjectSafetyViolation::Method(name, ..) => {
1008 err.help(&format!("consider moving `{}` to another trait", name));
1013 pub fn spans(&self) -> SmallVec<[Span; 1]> {
1014 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
1015 // diagnostics use a `note` instead of a `span_label`.
1017 ObjectSafetyViolation::SupertraitSelf(spans)
1018 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
1019 ObjectSafetyViolation::AssocConst(_, span)
1020 | ObjectSafetyViolation::GAT(_, span)
1021 | ObjectSafetyViolation::Method(_, _, span)
1022 if *span != DUMMY_SP =>
1031 /// Reasons a method might not be object-safe.
1032 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
1033 pub enum MethodViolationCode {
1034 /// e.g., `fn foo()`
1035 StaticMethod(Option<(/* add &self */ (String, Span), /* add Self: Sized */ (String, Span))>),
1037 /// e.g., `fn foo(&self, x: Self)`
1038 ReferencesSelfInput(Option<Span>),
1040 /// e.g., `fn foo(&self) -> Self`
1041 ReferencesSelfOutput,
1043 /// e.g., `fn foo(&self) -> impl Sized`
1044 ReferencesImplTraitInTrait,
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.