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::interpret::ErrorHandled;
13 use crate::ty::subst::SubstsRef;
14 use crate::ty::{self, AdtKind, Ty, TyCtxt};
17 use rustc_hir::def_id::DefId;
18 use rustc_span::symbol::Symbol;
19 use rustc_span::{Span, DUMMY_SP};
20 use smallvec::SmallVec;
27 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
29 pub type ChalkCanonicalGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>;
31 pub use self::ImplSource::*;
32 pub use self::ObligationCauseCode::*;
34 pub use self::chalk::{
35 ChalkEnvironmentAndGoal, ChalkEnvironmentClause, RustInterner as ChalkRustInterner,
38 /// Depending on the stage of compilation, we want projection to be
39 /// more or less conservative.
40 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
42 /// At type-checking time, we refuse to project any associated
43 /// type that is marked `default`. Non-`default` ("final") types
44 /// are always projected. This is necessary in general for
45 /// soundness of specialization. However, we *could* allow
46 /// projections in fully-monomorphic cases. We choose not to,
47 /// because we prefer for `default type` to force the type
48 /// definition to be treated abstractly by any consumers of the
49 /// impl. Concretely, that means that the following example will
57 /// impl<T> Assoc for T {
58 /// default type Output = bool;
62 /// let <() as Assoc>::Output = true;
67 /// At codegen time, all monomorphic projections will succeed.
68 /// Also, `impl Trait` is normalized to the concrete type,
69 /// which has to be already collected by type-checking.
71 /// NOTE: as `impl Trait`'s concrete type should *never*
72 /// be observable directly by the user, `Reveal::All`
73 /// should not be used by checks which may expose
74 /// type equality or type contents to the user.
75 /// There are some exceptions, e.g., around OIBITS and
76 /// transmute-checking, which expose some details, but
77 /// not the whole concrete type of the `impl Trait`.
81 /// The reason why we incurred this obligation; used for error reporting.
83 /// As the happy path does not care about this struct, storing this on the heap
84 /// ends up increasing performance.
86 /// We do not want to intern this as there are a lot of obligation causes which
87 /// only live for a short period of time.
88 #[derive(Clone, PartialEq, Eq, Hash, Lift)]
89 pub struct ObligationCause<'tcx> {
90 /// `None` for `ObligationCause::dummy`, `Some` otherwise.
91 data: Option<Rc<ObligationCauseData<'tcx>>>,
94 const DUMMY_OBLIGATION_CAUSE_DATA: ObligationCauseData<'static> =
95 ObligationCauseData { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation };
97 // Correctly format `ObligationCause::dummy`.
98 impl<'tcx> fmt::Debug for ObligationCause<'tcx> {
99 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
100 ObligationCauseData::fmt(self, f)
104 impl Deref for ObligationCause<'tcx> {
105 type Target = ObligationCauseData<'tcx>;
108 fn deref(&self) -> &Self::Target {
109 self.data.as_deref().unwrap_or(&DUMMY_OBLIGATION_CAUSE_DATA)
113 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
114 pub struct ObligationCauseData<'tcx> {
117 /// The ID of the fn body that triggered this obligation. This is
118 /// used for region obligations to determine the precise
119 /// environment in which the region obligation should be evaluated
120 /// (in particular, closures can add new assumptions). See the
121 /// field `region_obligations` of the `FulfillmentContext` for more
123 pub body_id: hir::HirId,
125 pub code: ObligationCauseCode<'tcx>,
128 impl<'tcx> ObligationCause<'tcx> {
133 code: ObligationCauseCode<'tcx>,
134 ) -> ObligationCause<'tcx> {
135 ObligationCause { data: Some(Rc::new(ObligationCauseData { span, body_id, code })) }
138 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
139 ObligationCause::new(span, body_id, MiscObligation)
142 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
143 ObligationCause::new(span, hir::CRATE_HIR_ID, MiscObligation)
147 pub fn dummy() -> ObligationCause<'tcx> {
148 ObligationCause { data: None }
151 pub fn make_mut(&mut self) -> &mut ObligationCauseData<'tcx> {
152 Rc::make_mut(self.data.get_or_insert_with(|| Rc::new(DUMMY_OBLIGATION_CAUSE_DATA)))
155 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
157 ObligationCauseCode::CompareImplMethodObligation { .. }
158 | ObligationCauseCode::MainFunctionType
159 | ObligationCauseCode::StartFunctionType => {
160 tcx.sess.source_map().guess_head_span(self.span)
162 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
171 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
172 pub struct UnifyReceiverContext<'tcx> {
173 pub assoc_item: ty::AssocItem,
174 pub param_env: ty::ParamEnv<'tcx>,
175 pub substs: SubstsRef<'tcx>,
178 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
179 pub enum ObligationCauseCode<'tcx> {
180 /// Not well classified or should be obvious from the span.
183 /// A slice or array is WF only if `T: Sized`.
186 /// A tuple is WF only if its middle elements are `Sized`.
189 /// This is the trait reference from the given projection.
190 ProjectionWf(ty::ProjectionTy<'tcx>),
192 /// In an impl of trait `X` for type `Y`, type `Y` must
193 /// also implement all supertraits of `X`.
194 ItemObligation(DefId),
196 /// Like `ItemObligation`, but with extra detail on the source of the obligation.
197 BindingObligation(DefId, Span),
199 /// A type like `&'a T` is WF only if `T: 'a`.
200 ReferenceOutlivesReferent(Ty<'tcx>),
202 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
203 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
205 /// Obligation incurred due to an object cast.
206 ObjectCastObligation(/* Object type */ Ty<'tcx>),
208 /// Obligation incurred due to a coercion.
214 /// Various cases where expressions must be `Sized` / `Copy` / etc.
215 /// `L = X` implies that `L` is `Sized`.
217 /// `(x1, .., xn)` must be `Sized`.
218 TupleInitializerSized,
219 /// `S { ... }` must be `Sized`.
220 StructInitializerSized,
221 /// Type of each variable must be `Sized`.
222 VariableType(hir::HirId),
223 /// Argument type must be `Sized`.
224 SizedArgumentType(Option<Span>),
225 /// Return type must be `Sized`.
227 /// Yield type must be `Sized`.
229 /// Inline asm operand type must be `Sized`.
231 /// `[T, ..n]` implies that `T` must be `Copy`.
232 /// If `true`, suggest `const_in_array_repeat_expressions` feature flag.
235 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
242 /// Constant expressions must be sized.
245 /// `static` items must have `Sync` type.
248 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
250 ImplDerivedObligation(DerivedObligationCause<'tcx>),
252 DerivedObligation(DerivedObligationCause<'tcx>),
254 /// Error derived when matching traits/impls; see ObligationCause for more details
255 CompareImplConstObligation,
257 /// Error derived when matching traits/impls; see ObligationCause for more details
258 CompareImplMethodObligation {
260 impl_item_def_id: DefId,
261 trait_item_def_id: DefId,
264 /// Error derived when matching traits/impls; see ObligationCause for more details
265 CompareImplTypeObligation {
267 impl_item_def_id: DefId,
268 trait_item_def_id: DefId,
271 /// Checking that this expression can be assigned where it needs to be
272 // FIXME(eddyb) #11161 is the original Expr required?
275 /// Computing common supertype in the arms of a match expression
276 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
278 /// Type error arising from type checking a pattern against an expected type.
280 /// The span of the scrutinee or type expression which caused the `root_ty` type.
282 /// The root expected type induced by a scrutinee or type expression.
284 /// Whether the `Span` came from an expression or a type expression.
288 /// Constants in patterns must have `Structural` type.
289 ConstPatternStructural,
291 /// Computing common supertype in an if expression
292 IfExpression(Box<IfExpressionCause>),
294 /// Computing common supertype of an if expression with no else counter-part
295 IfExpressionWithNoElse,
297 /// `main` has wrong type
300 /// `start` has wrong type
303 /// Intrinsic has wrong type
309 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
311 /// `return` with no expression
314 /// `return` with an expression
315 ReturnValue(hir::HirId),
317 /// Return type of this function
320 /// Block implicit return
321 BlockTailExpression(hir::HirId),
323 /// #[feature(trivial_bounds)] is not enabled
327 impl ObligationCauseCode<'_> {
328 // Return the base obligation, ignoring derived obligations.
329 pub fn peel_derives(&self) -> &Self {
330 let mut base_cause = self;
331 while let BuiltinDerivedObligation(cause)
332 | ImplDerivedObligation(cause)
333 | DerivedObligation(cause) = base_cause
335 base_cause = &cause.parent_code;
341 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
342 #[cfg(target_arch = "x86_64")]
343 static_assert_size!(ObligationCauseCode<'_>, 32);
345 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
346 pub struct MatchExpressionArmCause<'tcx> {
348 pub source: hir::MatchSource,
349 pub prior_arms: Vec<Span>,
350 pub last_ty: Ty<'tcx>,
351 pub scrut_hir_id: hir::HirId,
354 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
355 pub struct IfExpressionCause {
357 pub outer: Option<Span>,
358 pub semicolon: Option<Span>,
361 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
362 pub struct DerivedObligationCause<'tcx> {
363 /// The trait reference of the parent obligation that led to the
364 /// current obligation. Note that only trait obligations lead to
365 /// derived obligations, so we just store the trait reference here
367 pub parent_trait_ref: ty::PolyTraitRef<'tcx>,
369 /// The parent trait had this cause.
370 pub parent_code: Rc<ObligationCauseCode<'tcx>>,
373 #[derive(Clone, Debug, TypeFoldable, Lift)]
374 pub enum SelectionError<'tcx> {
376 OutputTypeParameterMismatch(
377 ty::PolyTraitRef<'tcx>,
378 ty::PolyTraitRef<'tcx>,
379 ty::error::TypeError<'tcx>,
381 TraitNotObjectSafe(DefId),
382 ConstEvalFailure(ErrorHandled),
386 /// When performing resolution, it is typically the case that there
387 /// can be one of three outcomes:
389 /// - `Ok(Some(r))`: success occurred with result `r`
390 /// - `Ok(None)`: could not definitely determine anything, usually due
391 /// to inconclusive type inference.
392 /// - `Err(e)`: error `e` occurred
393 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
395 /// Given the successful resolution of an obligation, the `ImplSource`
396 /// indicates where the impl comes from.
398 /// For example, the obligation may be satisfied by a specific impl (case A),
399 /// or it may be relative to some bound that is in scope (case B).
402 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
403 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
404 /// impl Clone for i32 { ... } // Impl_3
406 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
407 /// // Case A: Vtable points at a specific impl. Only possible when
408 /// // type is concretely known. If the impl itself has bounded
409 /// // type parameters, Vtable will carry resolutions for those as well:
410 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
412 /// // Case A: ImplSource points at a specific impl. Only possible when
413 /// // type is concretely known. If the impl itself has bounded
414 /// // type parameters, ImplSource will carry resolutions for those as well:
415 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
417 /// // Case B: ImplSource must be provided by caller. This applies when
418 /// // type is a type parameter.
419 /// param.clone(); // ImplSourceParam
421 /// // Case C: A mix of cases A and B.
422 /// mixed.clone(); // ImplSource(Impl_1, [ImplSourceParam])
426 /// ### The type parameter `N`
428 /// See explanation on `ImplSourceUserDefinedData`.
429 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
430 pub enum ImplSource<'tcx, N> {
431 /// ImplSource identifying a particular impl.
432 ImplSourceUserDefined(ImplSourceUserDefinedData<'tcx, N>),
434 /// ImplSource for auto trait implementations.
435 /// This carries the information and nested obligations with regards
436 /// to an auto implementation for a trait `Trait`. The nested obligations
437 /// ensure the trait implementation holds for all the constituent types.
438 ImplSourceAutoImpl(ImplSourceAutoImplData<N>),
440 /// Successful resolution to an obligation provided by the caller
441 /// for some type parameter. The `Vec<N>` represents the
442 /// obligations incurred from normalizing the where-clause (if
444 ImplSourceParam(Vec<N>),
446 /// Virtual calls through an object.
447 ImplSourceObject(ImplSourceObjectData<'tcx, N>),
449 /// Successful resolution for a builtin trait.
450 ImplSourceBuiltin(ImplSourceBuiltinData<N>),
452 /// ImplSource automatically generated for a closure. The `DefId` is the ID
453 /// of the closure expression. This is a `ImplSourceUserDefined` in spirit, but the
454 /// impl is generated by the compiler and does not appear in the source.
455 ImplSourceClosure(ImplSourceClosureData<'tcx, N>),
457 /// Same as above, but for a function pointer type with the given signature.
458 ImplSourceFnPointer(ImplSourceFnPointerData<'tcx, N>),
460 /// ImplSource for a builtin `DeterminantKind` trait implementation.
461 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData),
463 /// ImplSource automatically generated for a generator.
464 ImplSourceGenerator(ImplSourceGeneratorData<'tcx, N>),
466 /// ImplSource for a trait alias.
467 ImplSourceTraitAlias(ImplSourceTraitAliasData<'tcx, N>),
470 impl<'tcx, N> ImplSource<'tcx, N> {
471 pub fn nested_obligations(self) -> Vec<N> {
473 ImplSourceUserDefined(i) => i.nested,
474 ImplSourceParam(n) => n,
475 ImplSourceBuiltin(i) => i.nested,
476 ImplSourceAutoImpl(d) => d.nested,
477 ImplSourceClosure(c) => c.nested,
478 ImplSourceGenerator(c) => c.nested,
479 ImplSourceObject(d) => d.nested,
480 ImplSourceFnPointer(d) => d.nested,
481 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => Vec::new(),
482 ImplSourceTraitAlias(d) => d.nested,
486 pub fn borrow_nested_obligations(&self) -> &[N] {
488 ImplSourceUserDefined(i) => &i.nested[..],
489 ImplSourceParam(n) => &n[..],
490 ImplSourceBuiltin(i) => &i.nested[..],
491 ImplSourceAutoImpl(d) => &d.nested[..],
492 ImplSourceClosure(c) => &c.nested[..],
493 ImplSourceGenerator(c) => &c.nested[..],
494 ImplSourceObject(d) => &d.nested[..],
495 ImplSourceFnPointer(d) => &d.nested[..],
496 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => &[],
497 ImplSourceTraitAlias(d) => &d.nested[..],
501 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
506 ImplSourceUserDefined(i) => ImplSourceUserDefined(ImplSourceUserDefinedData {
507 impl_def_id: i.impl_def_id,
509 nested: i.nested.into_iter().map(f).collect(),
511 ImplSourceParam(n) => ImplSourceParam(n.into_iter().map(f).collect()),
512 ImplSourceBuiltin(i) => ImplSourceBuiltin(ImplSourceBuiltinData {
513 nested: i.nested.into_iter().map(f).collect(),
515 ImplSourceObject(o) => ImplSourceObject(ImplSourceObjectData {
516 upcast_trait_ref: o.upcast_trait_ref,
517 vtable_base: o.vtable_base,
518 nested: o.nested.into_iter().map(f).collect(),
520 ImplSourceAutoImpl(d) => ImplSourceAutoImpl(ImplSourceAutoImplData {
521 trait_def_id: d.trait_def_id,
522 nested: d.nested.into_iter().map(f).collect(),
524 ImplSourceClosure(c) => ImplSourceClosure(ImplSourceClosureData {
525 closure_def_id: c.closure_def_id,
527 nested: c.nested.into_iter().map(f).collect(),
529 ImplSourceGenerator(c) => ImplSourceGenerator(ImplSourceGeneratorData {
530 generator_def_id: c.generator_def_id,
532 nested: c.nested.into_iter().map(f).collect(),
534 ImplSourceFnPointer(p) => ImplSourceFnPointer(ImplSourceFnPointerData {
536 nested: p.nested.into_iter().map(f).collect(),
538 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => {
539 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData)
541 ImplSourceTraitAlias(d) => ImplSourceTraitAlias(ImplSourceTraitAliasData {
542 alias_def_id: d.alias_def_id,
544 nested: d.nested.into_iter().map(f).collect(),
550 /// Identifies a particular impl in the source, along with a set of
551 /// substitutions from the impl's type/lifetime parameters. The
552 /// `nested` vector corresponds to the nested obligations attached to
553 /// the impl's type parameters.
555 /// The type parameter `N` indicates the type used for "nested
556 /// obligations" that are required by the impl. During type-check, this
557 /// is `Obligation`, as one might expect. During codegen, however, this
558 /// is `()`, because codegen only requires a shallow resolution of an
559 /// impl, and nested obligations are satisfied later.
560 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
561 pub struct ImplSourceUserDefinedData<'tcx, N> {
562 pub impl_def_id: DefId,
563 pub substs: SubstsRef<'tcx>,
567 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
568 pub struct ImplSourceGeneratorData<'tcx, N> {
569 pub generator_def_id: DefId,
570 pub substs: SubstsRef<'tcx>,
571 /// Nested obligations. This can be non-empty if the generator
572 /// signature contains associated types.
576 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
577 pub struct ImplSourceClosureData<'tcx, N> {
578 pub closure_def_id: DefId,
579 pub substs: SubstsRef<'tcx>,
580 /// Nested obligations. This can be non-empty if the closure
581 /// signature contains associated types.
585 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
586 pub struct ImplSourceAutoImplData<N> {
587 pub trait_def_id: DefId,
591 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
592 pub struct ImplSourceBuiltinData<N> {
596 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
597 pub struct ImplSourceObjectData<'tcx, N> {
598 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
599 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
601 /// The vtable is formed by concatenating together the method lists of
602 /// the base object trait and all supertraits; this is the start of
603 /// `upcast_trait_ref`'s methods in that vtable.
604 pub vtable_base: usize,
609 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
610 pub struct ImplSourceFnPointerData<'tcx, N> {
615 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
616 #[derive(Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
617 pub struct ImplSourceDiscriminantKindData;
619 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable, Lift)]
620 pub struct ImplSourceTraitAliasData<'tcx, N> {
621 pub alias_def_id: DefId,
622 pub substs: SubstsRef<'tcx>,
626 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
627 pub enum ObjectSafetyViolation {
628 /// `Self: Sized` declared on the trait.
629 SizedSelf(SmallVec<[Span; 1]>),
631 /// Supertrait reference references `Self` an in illegal location
632 /// (e.g., `trait Foo : Bar<Self>`).
633 SupertraitSelf(SmallVec<[Span; 1]>),
635 /// Method has something illegal.
636 Method(Symbol, MethodViolationCode, Span),
638 /// Associated const.
639 AssocConst(Symbol, Span),
642 impl ObjectSafetyViolation {
643 pub fn error_msg(&self) -> Cow<'static, str> {
645 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
646 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
647 if spans.iter().any(|sp| *sp != DUMMY_SP) {
648 "it uses `Self` as a type parameter in this".into()
650 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
654 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
655 format!("associated function `{}` has no `self` parameter", name).into()
657 ObjectSafetyViolation::Method(
659 MethodViolationCode::ReferencesSelfInput(_),
661 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
662 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
663 format!("method `{}` references the `Self` type in this parameter", name).into()
665 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
666 format!("method `{}` references the `Self` type in its return type", name).into()
668 ObjectSafetyViolation::Method(
670 MethodViolationCode::WhereClauseReferencesSelf,
673 format!("method `{}` references the `Self` type in its `where` clause", name).into()
675 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
676 format!("method `{}` has generic type parameters", name).into()
678 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
679 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
681 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
682 format!("it contains associated `const` `{}`", name).into()
684 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
688 pub fn solution(&self) -> Option<(String, Option<(String, Span)>)> {
690 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {
693 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(sugg), _) => (
695 "consider turning `{}` into a method by giving it a `&self` argument or \
696 constraining it so it does not apply to trait objects",
699 sugg.map(|(sugg, sp)| (sugg.to_string(), sp)),
701 ObjectSafetyViolation::Method(
703 MethodViolationCode::UndispatchableReceiver,
706 format!("consider changing method `{}`'s `self` parameter to be `&self`", name),
707 Some(("&Self".to_string(), span)),
709 ObjectSafetyViolation::AssocConst(name, _)
710 | ObjectSafetyViolation::Method(name, ..) => {
711 (format!("consider moving `{}` to another trait", name), None)
716 pub fn spans(&self) -> SmallVec<[Span; 1]> {
717 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
718 // diagnostics use a `note` instead of a `span_label`.
720 ObjectSafetyViolation::SupertraitSelf(spans)
721 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
722 ObjectSafetyViolation::AssocConst(_, span)
723 | ObjectSafetyViolation::Method(_, _, span)
724 if *span != DUMMY_SP =>
733 /// Reasons a method might not be object-safe.
734 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
735 pub enum MethodViolationCode {
737 StaticMethod(Option<(&'static str, Span)>),
739 /// e.g., `fn foo(&self, x: Self)`
740 ReferencesSelfInput(usize),
742 /// e.g., `fn foo(&self) -> Self`
743 ReferencesSelfOutput,
745 /// e.g., `fn foo(&self) where Self: Clone`
746 WhereClauseReferencesSelf,
748 /// e.g., `fn foo<A>()`
751 /// the method's receiver (`self` argument) can't be dispatched on
752 UndispatchableReceiver,