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;
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};
16 use rustc_errors::{Applicability, DiagnosticBuilder};
18 use rustc_hir::def_id::DefId;
19 use rustc_hir::Constness;
20 use rustc_span::symbol::Symbol;
21 use rustc_span::{Span, DUMMY_SP};
22 use smallvec::SmallVec;
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
56 /// impl<T> Assoc for T {
57 /// default type Output = bool;
61 /// let <() as Assoc>::Output = true;
66 /// At codegen time, all monomorphic projections will succeed.
67 /// Also, `impl Trait` is normalized to the concrete type,
68 /// which has to be already collected by type-checking.
70 /// NOTE: as `impl Trait`'s concrete type should *never*
71 /// be observable directly by the user, `Reveal::All`
72 /// should not be used by checks which may expose
73 /// type equality or type contents to the user.
74 /// There are some exceptions, e.g., around auto traits and
75 /// transmute-checking, which expose some details, but
76 /// not the whole concrete type of the `impl Trait`.
80 /// The reason why we incurred this obligation; used for error reporting.
82 /// As the happy path does not care about this struct, storing this on the heap
83 /// ends up increasing performance.
85 /// We do not want to intern this as there are a lot of obligation causes which
86 /// only live for a short period of time.
87 #[derive(Clone, PartialEq, Eq, Hash, Lift)]
88 pub struct ObligationCause<'tcx> {
89 /// `None` for `ObligationCause::dummy`, `Some` otherwise.
90 data: Option<Rc<ObligationCauseData<'tcx>>>,
93 const DUMMY_OBLIGATION_CAUSE_DATA: ObligationCauseData<'static> =
94 ObligationCauseData { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation };
96 // Correctly format `ObligationCause::dummy`.
97 impl<'tcx> fmt::Debug for ObligationCause<'tcx> {
98 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
99 ObligationCauseData::fmt(self, f)
103 impl Deref for ObligationCause<'tcx> {
104 type Target = ObligationCauseData<'tcx>;
107 fn deref(&self) -> &Self::Target {
108 self.data.as_deref().unwrap_or(&DUMMY_OBLIGATION_CAUSE_DATA)
112 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
113 pub struct ObligationCauseData<'tcx> {
116 /// The ID of the fn body that triggered this obligation. This is
117 /// used for region obligations to determine the precise
118 /// environment in which the region obligation should be evaluated
119 /// (in particular, closures can add new assumptions). See the
120 /// field `region_obligations` of the `FulfillmentContext` for more
122 pub body_id: hir::HirId,
124 pub code: ObligationCauseCode<'tcx>,
127 impl<'tcx> ObligationCause<'tcx> {
132 code: ObligationCauseCode<'tcx>,
133 ) -> ObligationCause<'tcx> {
134 ObligationCause { data: Some(Rc::new(ObligationCauseData { span, body_id, code })) }
137 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
138 ObligationCause::new(span, body_id, MiscObligation)
141 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
142 ObligationCause::new(span, hir::CRATE_HIR_ID, MiscObligation)
146 pub fn dummy() -> ObligationCause<'tcx> {
147 ObligationCause { data: None }
150 pub fn make_mut(&mut self) -> &mut ObligationCauseData<'tcx> {
151 Rc::make_mut(self.data.get_or_insert_with(|| Rc::new(DUMMY_OBLIGATION_CAUSE_DATA)))
154 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
156 ObligationCauseCode::CompareImplMethodObligation { .. }
157 | ObligationCauseCode::MainFunctionType
158 | ObligationCauseCode::StartFunctionType => {
159 tcx.sess.source_map().guess_head_span(self.span)
161 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
170 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
171 pub struct UnifyReceiverContext<'tcx> {
172 pub assoc_item: ty::AssocItem,
173 pub param_env: ty::ParamEnv<'tcx>,
174 pub substs: SubstsRef<'tcx>,
177 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
178 pub enum ObligationCauseCode<'tcx> {
179 /// Not well classified or should be obvious from the span.
182 /// A slice or array is WF only if `T: Sized`.
185 /// A tuple is WF only if its middle elements are `Sized`.
188 /// This is the trait reference from the given projection.
189 ProjectionWf(ty::ProjectionTy<'tcx>),
191 /// In an impl of trait `X` for type `Y`, type `Y` must
192 /// also implement all supertraits of `X`.
193 ItemObligation(DefId),
195 /// Like `ItemObligation`, but with extra detail on the source of the obligation.
196 BindingObligation(DefId, Span),
198 /// A type like `&'a T` is WF only if `T: 'a`.
199 ReferenceOutlivesReferent(Ty<'tcx>),
201 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
202 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
204 /// Obligation incurred due to an object cast.
205 ObjectCastObligation(/* Object type */ Ty<'tcx>),
207 /// Obligation incurred due to a coercion.
213 /// Various cases where expressions must be `Sized` / `Copy` / etc.
214 /// `L = X` implies that `L` is `Sized`.
216 /// `(x1, .., xn)` must be `Sized`.
217 TupleInitializerSized,
218 /// `S { ... }` must be `Sized`.
219 StructInitializerSized,
220 /// Type of each variable must be `Sized`.
221 VariableType(hir::HirId),
222 /// Argument type must be `Sized`.
223 SizedArgumentType(Option<Span>),
224 /// Return type must be `Sized`.
226 /// Yield type must be `Sized`.
228 /// Inline asm operand type must be `Sized`.
230 /// `[T, ..n]` implies that `T` must be `Copy`.
231 /// If the function in the array repeat expression is a `const fn`,
232 /// display a help message suggesting to move the function call to a
233 /// new `const` item while saying that `T` doesn't implement `Copy`.
236 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
243 /// Constant expressions must be sized.
246 /// `static` items must have `Sync` type.
249 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
251 ImplDerivedObligation(DerivedObligationCause<'tcx>),
253 DerivedObligation(DerivedObligationCause<'tcx>),
255 /// Error derived when matching traits/impls; see ObligationCause for more details
256 CompareImplConstObligation,
258 /// Error derived when matching traits/impls; see ObligationCause for more details
259 CompareImplMethodObligation {
261 impl_item_def_id: DefId,
262 trait_item_def_id: DefId,
265 /// Error derived when matching traits/impls; see ObligationCause for more details
266 CompareImplTypeObligation {
268 impl_item_def_id: DefId,
269 trait_item_def_id: DefId,
272 /// Checking that this expression can be assigned where it needs to be
273 // FIXME(eddyb) #11161 is the original Expr required?
276 /// Computing common supertype in the arms of a match expression
277 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
279 /// Type error arising from type checking a pattern against an expected type.
281 /// The span of the scrutinee or type expression which caused the `root_ty` type.
283 /// The root expected type induced by a scrutinee or type expression.
285 /// Whether the `Span` came from an expression or a type expression.
289 /// Constants in patterns must have `Structural` type.
290 ConstPatternStructural,
292 /// Computing common supertype in an if expression
293 IfExpression(Box<IfExpressionCause>),
295 /// Computing common supertype of an if expression with no else counter-part
296 IfExpressionWithNoElse,
298 /// `main` has wrong type
301 /// `start` has wrong type
304 /// Intrinsic has wrong type
310 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
312 /// `return` with no expression
315 /// `return` with an expression
316 ReturnValue(hir::HirId),
318 /// Return type of this function
321 /// Block implicit return
322 BlockTailExpression(hir::HirId),
324 /// #[feature(trivial_bounds)] is not enabled
327 /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
331 impl ObligationCauseCode<'_> {
332 // Return the base obligation, ignoring derived obligations.
333 pub fn peel_derives(&self) -> &Self {
334 let mut base_cause = self;
335 while let BuiltinDerivedObligation(cause)
336 | ImplDerivedObligation(cause)
337 | DerivedObligation(cause) = base_cause
339 base_cause = &cause.parent_code;
345 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
346 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
347 static_assert_size!(ObligationCauseCode<'_>, 40);
349 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
350 pub enum StatementAsExpression {
355 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
356 type Lifted = StatementAsExpression;
357 fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
362 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
363 pub struct MatchExpressionArmCause<'tcx> {
365 pub scrut_span: Span,
366 pub semi_span: Option<(Span, StatementAsExpression)>,
367 pub source: hir::MatchSource,
368 pub prior_arms: Vec<Span>,
369 pub last_ty: Ty<'tcx>,
370 pub scrut_hir_id: hir::HirId,
371 pub opt_suggest_box_span: Option<Span>,
374 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
375 pub struct IfExpressionCause {
378 pub outer: Option<Span>,
379 pub semicolon: Option<(Span, StatementAsExpression)>,
380 pub opt_suggest_box_span: Option<Span>,
383 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
384 pub struct DerivedObligationCause<'tcx> {
385 /// The trait reference of the parent obligation that led to the
386 /// current obligation. Note that only trait obligations lead to
387 /// derived obligations, so we just store the trait reference here
389 pub parent_trait_ref: ty::PolyTraitRef<'tcx>,
391 /// The parent trait had this cause.
392 pub parent_code: Rc<ObligationCauseCode<'tcx>>,
395 #[derive(Clone, Debug, TypeFoldable, Lift)]
396 pub enum SelectionError<'tcx> {
398 OutputTypeParameterMismatch(
399 ty::PolyTraitRef<'tcx>,
400 ty::PolyTraitRef<'tcx>,
401 ty::error::TypeError<'tcx>,
403 TraitNotObjectSafe(DefId),
404 NotConstEvaluatable(NotConstEvaluatable),
408 /// When performing resolution, it is typically the case that there
409 /// can be one of three outcomes:
411 /// - `Ok(Some(r))`: success occurred with result `r`
412 /// - `Ok(None)`: could not definitely determine anything, usually due
413 /// to inconclusive type inference.
414 /// - `Err(e)`: error `e` occurred
415 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
417 /// Given the successful resolution of an obligation, the `ImplSource`
418 /// indicates where the impl comes from.
420 /// For example, the obligation may be satisfied by a specific impl (case A),
421 /// or it may be relative to some bound that is in scope (case B).
424 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
425 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
426 /// impl Clone for i32 { ... } // Impl_3
428 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
429 /// // Case A: Vtable points at a specific impl. Only possible when
430 /// // type is concretely known. If the impl itself has bounded
431 /// // type parameters, Vtable will carry resolutions for those as well:
432 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
434 /// // Case A: ImplSource points at a specific impl. Only possible when
435 /// // type is concretely known. If the impl itself has bounded
436 /// // type parameters, ImplSource will carry resolutions for those as well:
437 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
439 /// // Case B: ImplSource must be provided by caller. This applies when
440 /// // type is a type parameter.
441 /// param.clone(); // ImplSource::Param
443 /// // Case C: A mix of cases A and B.
444 /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param])
448 /// ### The type parameter `N`
450 /// See explanation on `ImplSourceUserDefinedData`.
451 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
452 pub enum ImplSource<'tcx, N> {
453 /// ImplSource identifying a particular impl.
454 UserDefined(ImplSourceUserDefinedData<'tcx, N>),
456 /// ImplSource for auto trait implementations.
457 /// This carries the information and nested obligations with regards
458 /// to an auto implementation for a trait `Trait`. The nested obligations
459 /// ensure the trait implementation holds for all the constituent types.
460 AutoImpl(ImplSourceAutoImplData<N>),
462 /// Successful resolution to an obligation provided by the caller
463 /// for some type parameter. The `Vec<N>` represents the
464 /// obligations incurred from normalizing the where-clause (if
466 Param(Vec<N>, Constness),
468 /// Virtual calls through an object.
469 Object(ImplSourceObjectData<'tcx, N>),
471 /// Successful resolution for a builtin trait.
472 Builtin(ImplSourceBuiltinData<N>),
474 /// ImplSource automatically generated for a closure. The `DefId` is the ID
475 /// of the closure expression. This is a `ImplSource::UserDefined` in spirit, but the
476 /// impl is generated by the compiler and does not appear in the source.
477 Closure(ImplSourceClosureData<'tcx, N>),
479 /// Same as above, but for a function pointer type with the given signature.
480 FnPointer(ImplSourceFnPointerData<'tcx, N>),
482 /// ImplSource for a builtin `DeterminantKind` trait implementation.
483 DiscriminantKind(ImplSourceDiscriminantKindData),
485 /// ImplSource for a builtin `Pointee` trait implementation.
486 Pointee(ImplSourcePointeeData),
488 /// ImplSource automatically generated for a generator.
489 Generator(ImplSourceGeneratorData<'tcx, N>),
491 /// ImplSource for a trait alias.
492 TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
495 impl<'tcx, N> ImplSource<'tcx, N> {
496 pub fn nested_obligations(self) -> Vec<N> {
498 ImplSource::UserDefined(i) => i.nested,
499 ImplSource::Param(n, _) => n,
500 ImplSource::Builtin(i) => i.nested,
501 ImplSource::AutoImpl(d) => d.nested,
502 ImplSource::Closure(c) => c.nested,
503 ImplSource::Generator(c) => c.nested,
504 ImplSource::Object(d) => d.nested,
505 ImplSource::FnPointer(d) => d.nested,
506 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
507 | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
508 ImplSource::TraitAlias(d) => d.nested,
512 pub fn borrow_nested_obligations(&self) -> &[N] {
514 ImplSource::UserDefined(i) => &i.nested[..],
515 ImplSource::Param(n, _) => &n[..],
516 ImplSource::Builtin(i) => &i.nested[..],
517 ImplSource::AutoImpl(d) => &d.nested[..],
518 ImplSource::Closure(c) => &c.nested[..],
519 ImplSource::Generator(c) => &c.nested[..],
520 ImplSource::Object(d) => &d.nested[..],
521 ImplSource::FnPointer(d) => &d.nested[..],
522 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
523 | ImplSource::Pointee(ImplSourcePointeeData) => &[],
524 ImplSource::TraitAlias(d) => &d.nested[..],
528 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
533 ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
534 impl_def_id: i.impl_def_id,
536 nested: i.nested.into_iter().map(f).collect(),
538 ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
539 ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
540 nested: i.nested.into_iter().map(f).collect(),
542 ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
543 upcast_trait_ref: o.upcast_trait_ref,
544 vtable_base: o.vtable_base,
545 nested: o.nested.into_iter().map(f).collect(),
547 ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
548 trait_def_id: d.trait_def_id,
549 nested: d.nested.into_iter().map(f).collect(),
551 ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
552 closure_def_id: c.closure_def_id,
554 nested: c.nested.into_iter().map(f).collect(),
556 ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
557 generator_def_id: c.generator_def_id,
559 nested: c.nested.into_iter().map(f).collect(),
561 ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
563 nested: p.nested.into_iter().map(f).collect(),
565 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
566 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
568 ImplSource::Pointee(ImplSourcePointeeData) => {
569 ImplSource::Pointee(ImplSourcePointeeData)
571 ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
572 alias_def_id: d.alias_def_id,
574 nested: d.nested.into_iter().map(f).collect(),
580 /// Identifies a particular impl in the source, along with a set of
581 /// substitutions from the impl's type/lifetime parameters. The
582 /// `nested` vector corresponds to the nested obligations attached to
583 /// the impl's type parameters.
585 /// The type parameter `N` indicates the type used for "nested
586 /// obligations" that are required by the impl. During type-check, this
587 /// is `Obligation`, as one might expect. During codegen, however, this
588 /// is `()`, because codegen only requires a shallow resolution of an
589 /// impl, and nested obligations are satisfied later.
590 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
591 pub struct ImplSourceUserDefinedData<'tcx, N> {
592 pub impl_def_id: DefId,
593 pub substs: SubstsRef<'tcx>,
597 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
598 pub struct ImplSourceGeneratorData<'tcx, N> {
599 pub generator_def_id: DefId,
600 pub substs: SubstsRef<'tcx>,
601 /// Nested obligations. This can be non-empty if the generator
602 /// signature contains associated types.
606 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
607 pub struct ImplSourceClosureData<'tcx, N> {
608 pub closure_def_id: DefId,
609 pub substs: SubstsRef<'tcx>,
610 /// Nested obligations. This can be non-empty if the closure
611 /// signature contains associated types.
615 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
616 pub struct ImplSourceAutoImplData<N> {
617 pub trait_def_id: DefId,
621 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
622 pub struct ImplSourceBuiltinData<N> {
626 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
627 pub struct ImplSourceObjectData<'tcx, N> {
628 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
629 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
631 /// The vtable is formed by concatenating together the method lists of
632 /// the base object trait and all supertraits; this is the start of
633 /// `upcast_trait_ref`'s methods in that vtable.
634 pub vtable_base: usize,
639 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
640 pub struct ImplSourceFnPointerData<'tcx, N> {
645 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
646 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
647 pub struct ImplSourceDiscriminantKindData;
649 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
650 pub struct ImplSourcePointeeData;
652 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
653 pub struct ImplSourceTraitAliasData<'tcx, N> {
654 pub alias_def_id: DefId,
655 pub substs: SubstsRef<'tcx>,
659 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
660 pub enum ObjectSafetyViolation {
661 /// `Self: Sized` declared on the trait.
662 SizedSelf(SmallVec<[Span; 1]>),
664 /// Supertrait reference references `Self` an in illegal location
665 /// (e.g., `trait Foo : Bar<Self>`).
666 SupertraitSelf(SmallVec<[Span; 1]>),
668 /// Method has something illegal.
669 Method(Symbol, MethodViolationCode, Span),
671 /// Associated const.
672 AssocConst(Symbol, Span),
678 impl ObjectSafetyViolation {
679 pub fn error_msg(&self) -> Cow<'static, str> {
681 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
682 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
683 if spans.iter().any(|sp| *sp != DUMMY_SP) {
684 "it uses `Self` as a type parameter".into()
686 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
690 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
691 format!("associated function `{}` has no `self` parameter", name).into()
693 ObjectSafetyViolation::Method(
695 MethodViolationCode::ReferencesSelfInput(_),
697 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
698 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
699 format!("method `{}` references the `Self` type in this parameter", name).into()
701 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
702 format!("method `{}` references the `Self` type in its return type", name).into()
704 ObjectSafetyViolation::Method(
706 MethodViolationCode::WhereClauseReferencesSelf,
709 format!("method `{}` references the `Self` type in its `where` clause", name).into()
711 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
712 format!("method `{}` has generic type parameters", name).into()
714 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
715 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
717 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
718 format!("it contains associated `const` `{}`", name).into()
720 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
721 ObjectSafetyViolation::GAT(name, _) => {
722 format!("it contains the generic associated type `{}`", name).into()
727 pub fn solution(&self, err: &mut DiagnosticBuilder<'_>) {
729 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
730 ObjectSafetyViolation::Method(
732 MethodViolationCode::StaticMethod(sugg, self_span, has_args),
738 "consider turning `{}` into a method by giving it a `&self` argument",
741 format!("&self{}", if has_args { ", " } else { "" }),
742 Applicability::MaybeIncorrect,
745 Some((sugg, span)) => {
749 "alternatively, consider constraining `{}` so it does not apply to \
754 Applicability::MaybeIncorrect,
759 "consider turning `{}` into a method by giving it a `&self` \
760 argument or constraining it so it does not apply to trait objects",
766 ObjectSafetyViolation::Method(
768 MethodViolationCode::UndispatchableReceiver,
774 "consider changing method `{}`'s `self` parameter to be `&self`",
778 Applicability::MachineApplicable,
781 ObjectSafetyViolation::AssocConst(name, _)
782 | ObjectSafetyViolation::GAT(name, _)
783 | ObjectSafetyViolation::Method(name, ..) => {
784 err.help(&format!("consider moving `{}` to another trait", name));
789 pub fn spans(&self) -> SmallVec<[Span; 1]> {
790 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
791 // diagnostics use a `note` instead of a `span_label`.
793 ObjectSafetyViolation::SupertraitSelf(spans)
794 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
795 ObjectSafetyViolation::AssocConst(_, span)
796 | ObjectSafetyViolation::GAT(_, span)
797 | ObjectSafetyViolation::Method(_, _, span)
798 if *span != DUMMY_SP =>
807 /// Reasons a method might not be object-safe.
808 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
809 pub enum MethodViolationCode {
811 StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),
813 /// e.g., `fn foo(&self, x: Self)`
814 ReferencesSelfInput(usize),
816 /// e.g., `fn foo(&self) -> Self`
817 ReferencesSelfOutput,
819 /// e.g., `fn foo(&self) where Self: Clone`
820 WhereClauseReferencesSelf,
822 /// e.g., `fn foo<A>()`
825 /// the method's receiver (`self` argument) can't be dispatched on
826 UndispatchableReceiver,