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::*;
33 pub use self::SelectionError::*;
35 pub use self::chalk::{
36 ChalkEnvironmentAndGoal, ChalkEnvironmentClause, RustInterner as ChalkRustInterner,
39 /// Depending on the stage of compilation, we want projection to be
40 /// more or less conservative.
41 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
43 /// At type-checking time, we refuse to project any associated
44 /// type that is marked `default`. Non-`default` ("final") types
45 /// are always projected. This is necessary in general for
46 /// soundness of specialization. However, we *could* allow
47 /// projections in fully-monomorphic cases. We choose not to,
48 /// because we prefer for `default type` to force the type
49 /// definition to be treated abstractly by any consumers of the
50 /// impl. Concretely, that means that the following example will
58 /// impl<T> Assoc for T {
59 /// default type Output = bool;
63 /// let <() as Assoc>::Output = true;
68 /// At codegen time, all monomorphic projections will succeed.
69 /// Also, `impl Trait` is normalized to the concrete type,
70 /// which has to be already collected by type-checking.
72 /// NOTE: as `impl Trait`'s concrete type should *never*
73 /// be observable directly by the user, `Reveal::All`
74 /// should not be used by checks which may expose
75 /// type equality or type contents to the user.
76 /// There are some exceptions, e.g., around OIBITS and
77 /// transmute-checking, which expose some details, but
78 /// not the whole concrete type of the `impl Trait`.
82 /// The reason why we incurred this obligation; used for error reporting.
84 /// As the happy path does not care about this struct, storing this on the heap
85 /// ends up increasing performance.
87 /// We do not want to intern this as there are a lot of obligation causes which
88 /// only live for a short period of time.
89 #[derive(Clone, PartialEq, Eq, Hash)]
90 pub struct ObligationCause<'tcx> {
91 /// `None` for `ObligationCause::dummy`, `Some` otherwise.
92 data: Option<Rc<ObligationCauseData<'tcx>>>,
95 const DUMMY_OBLIGATION_CAUSE_DATA: ObligationCauseData<'static> =
96 ObligationCauseData { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation };
98 // Correctly format `ObligationCause::dummy`.
99 impl<'tcx> fmt::Debug for ObligationCause<'tcx> {
100 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
101 ObligationCauseData::fmt(self, f)
105 impl Deref for ObligationCause<'tcx> {
106 type Target = ObligationCauseData<'tcx>;
109 fn deref(&self) -> &Self::Target {
110 self.data.as_deref().unwrap_or(&DUMMY_OBLIGATION_CAUSE_DATA)
114 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
115 pub struct ObligationCauseData<'tcx> {
118 /// The ID of the fn body that triggered this obligation. This is
119 /// used for region obligations to determine the precise
120 /// environment in which the region obligation should be evaluated
121 /// (in particular, closures can add new assumptions). See the
122 /// field `region_obligations` of the `FulfillmentContext` for more
124 pub body_id: hir::HirId,
126 pub code: ObligationCauseCode<'tcx>,
129 impl<'tcx> ObligationCause<'tcx> {
134 code: ObligationCauseCode<'tcx>,
135 ) -> ObligationCause<'tcx> {
136 ObligationCause { data: Some(Rc::new(ObligationCauseData { span, body_id, code })) }
139 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
140 ObligationCause::new(span, body_id, MiscObligation)
143 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
144 ObligationCause::new(span, hir::CRATE_HIR_ID, MiscObligation)
148 pub fn dummy() -> ObligationCause<'tcx> {
149 ObligationCause { data: None }
152 pub fn make_mut(&mut self) -> &mut ObligationCauseData<'tcx> {
153 Rc::make_mut(self.data.get_or_insert_with(|| Rc::new(DUMMY_OBLIGATION_CAUSE_DATA)))
156 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
158 ObligationCauseCode::CompareImplMethodObligation { .. }
159 | ObligationCauseCode::MainFunctionType
160 | ObligationCauseCode::StartFunctionType => {
161 tcx.sess.source_map().guess_head_span(self.span)
163 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
172 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
173 pub struct UnifyReceiverContext<'tcx> {
174 pub assoc_item: ty::AssocItem,
175 pub param_env: ty::ParamEnv<'tcx>,
176 pub substs: SubstsRef<'tcx>,
179 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
180 pub enum ObligationCauseCode<'tcx> {
181 /// Not well classified or should be obvious from the span.
184 /// A slice or array is WF only if `T: Sized`.
187 /// A tuple is WF only if its middle elements are `Sized`.
190 /// This is the trait reference from the given projection.
191 ProjectionWf(ty::ProjectionTy<'tcx>),
193 /// In an impl of trait `X` for type `Y`, type `Y` must
194 /// also implement all supertraits of `X`.
195 ItemObligation(DefId),
197 /// Like `ItemObligation`, but with extra detail on the source of the obligation.
198 BindingObligation(DefId, Span),
200 /// A type like `&'a T` is WF only if `T: 'a`.
201 ReferenceOutlivesReferent(Ty<'tcx>),
203 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
204 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
206 /// Obligation incurred due to an object cast.
207 ObjectCastObligation(/* Object type */ Ty<'tcx>),
209 /// Obligation incurred due to a coercion.
215 /// Various cases where expressions must be `Sized` / `Copy` / etc.
216 /// `L = X` implies that `L` is `Sized`.
218 /// `(x1, .., xn)` must be `Sized`.
219 TupleInitializerSized,
220 /// `S { ... }` must be `Sized`.
221 StructInitializerSized,
222 /// Type of each variable must be `Sized`.
223 VariableType(hir::HirId),
224 /// Argument type must be `Sized`.
225 SizedArgumentType(Option<Span>),
226 /// Return type must be `Sized`.
228 /// Yield type must be `Sized`.
230 /// Inline asm operand type must be `Sized`.
232 /// `[T, ..n]` implies that `T` must be `Copy`.
233 /// If `true`, suggest `const_in_array_repeat_expressions` feature flag.
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
328 impl ObligationCauseCode<'_> {
329 // Return the base obligation, ignoring derived obligations.
330 pub fn peel_derives(&self) -> &Self {
331 let mut base_cause = self;
332 while let BuiltinDerivedObligation(cause)
333 | ImplDerivedObligation(cause)
334 | DerivedObligation(cause) = base_cause
336 base_cause = &cause.parent_code;
342 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
343 #[cfg(target_arch = "x86_64")]
344 static_assert_size!(ObligationCauseCode<'_>, 32);
346 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
347 pub struct MatchExpressionArmCause<'tcx> {
349 pub source: hir::MatchSource,
350 pub prior_arms: Vec<Span>,
351 pub last_ty: Ty<'tcx>,
352 pub scrut_hir_id: hir::HirId,
355 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
356 pub struct IfExpressionCause {
358 pub outer: Option<Span>,
359 pub semicolon: Option<Span>,
362 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
363 pub struct DerivedObligationCause<'tcx> {
364 /// The trait reference of the parent obligation that led to the
365 /// current obligation. Note that only trait obligations lead to
366 /// derived obligations, so we just store the trait reference here
368 pub parent_trait_ref: ty::PolyTraitRef<'tcx>,
370 /// The parent trait had this cause.
371 pub parent_code: Rc<ObligationCauseCode<'tcx>>,
374 #[derive(Clone, Debug, TypeFoldable)]
375 pub enum SelectionError<'tcx> {
377 OutputTypeParameterMismatch(
378 ty::PolyTraitRef<'tcx>,
379 ty::PolyTraitRef<'tcx>,
380 ty::error::TypeError<'tcx>,
382 TraitNotObjectSafe(DefId),
383 ConstEvalFailure(ErrorHandled),
387 /// When performing resolution, it is typically the case that there
388 /// can be one of three outcomes:
390 /// - `Ok(Some(r))`: success occurred with result `r`
391 /// - `Ok(None)`: could not definitely determine anything, usually due
392 /// to inconclusive type inference.
393 /// - `Err(e)`: error `e` occurred
394 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
396 /// Given the successful resolution of an obligation, the `ImplSource`
397 /// indicates where the impl comes from.
399 /// For example, the obligation may be satisfied by a specific impl (case A),
400 /// or it may be relative to some bound that is in scope (case B).
403 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
404 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
405 /// impl Clone for i32 { ... } // Impl_3
407 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
408 /// // Case A: Vtable points at a specific impl. Only possible when
409 /// // type is concretely known. If the impl itself has bounded
410 /// // type parameters, Vtable will carry resolutions for those as well:
411 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
413 /// // Case A: ImplSource points at a specific impl. Only possible when
414 /// // type is concretely known. If the impl itself has bounded
415 /// // type parameters, ImplSource will carry resolutions for those as well:
416 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
418 /// // Case B: ImplSource must be provided by caller. This applies when
419 /// // type is a type parameter.
420 /// param.clone(); // ImplSourceParam
422 /// // Case C: A mix of cases A and B.
423 /// mixed.clone(); // ImplSource(Impl_1, [ImplSourceParam])
427 /// ### The type parameter `N`
429 /// See explanation on `ImplSourceUserDefinedData`.
430 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
431 pub enum ImplSource<'tcx, N> {
432 /// ImplSource identifying a particular impl.
433 ImplSourceUserDefined(ImplSourceUserDefinedData<'tcx, N>),
435 /// ImplSource for auto trait implementations.
436 /// This carries the information and nested obligations with regards
437 /// to an auto implementation for a trait `Trait`. The nested obligations
438 /// ensure the trait implementation holds for all the constituent types.
439 ImplSourceAutoImpl(ImplSourceAutoImplData<N>),
441 /// Successful resolution to an obligation provided by the caller
442 /// for some type parameter. The `Vec<N>` represents the
443 /// obligations incurred from normalizing the where-clause (if
445 ImplSourceParam(Vec<N>),
447 /// Virtual calls through an object.
448 ImplSourceObject(ImplSourceObjectData<'tcx, N>),
450 /// Successful resolution for a builtin trait.
451 ImplSourceBuiltin(ImplSourceBuiltinData<N>),
453 /// ImplSource automatically generated for a closure. The `DefId` is the ID
454 /// of the closure expression. This is a `ImplSourceUserDefined` in spirit, but the
455 /// impl is generated by the compiler and does not appear in the source.
456 ImplSourceClosure(ImplSourceClosureData<'tcx, N>),
458 /// Same as above, but for a function pointer type with the given signature.
459 ImplSourceFnPointer(ImplSourceFnPointerData<'tcx, N>),
461 /// ImplSource for a builtin `DeterminantKind` trait implementation.
462 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData),
464 /// ImplSource automatically generated for a generator.
465 ImplSourceGenerator(ImplSourceGeneratorData<'tcx, N>),
467 /// ImplSource for a trait alias.
468 ImplSourceTraitAlias(ImplSourceTraitAliasData<'tcx, N>),
471 impl<'tcx, N> ImplSource<'tcx, N> {
472 pub fn nested_obligations(self) -> Vec<N> {
474 ImplSourceUserDefined(i) => i.nested,
475 ImplSourceParam(n) => n,
476 ImplSourceBuiltin(i) => i.nested,
477 ImplSourceAutoImpl(d) => d.nested,
478 ImplSourceClosure(c) => c.nested,
479 ImplSourceGenerator(c) => c.nested,
480 ImplSourceObject(d) => d.nested,
481 ImplSourceFnPointer(d) => d.nested,
482 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => Vec::new(),
483 ImplSourceTraitAlias(d) => d.nested,
487 pub fn borrow_nested_obligations(&self) -> &[N] {
489 ImplSourceUserDefined(i) => &i.nested[..],
490 ImplSourceParam(n) => &n[..],
491 ImplSourceBuiltin(i) => &i.nested[..],
492 ImplSourceAutoImpl(d) => &d.nested[..],
493 ImplSourceClosure(c) => &c.nested[..],
494 ImplSourceGenerator(c) => &c.nested[..],
495 ImplSourceObject(d) => &d.nested[..],
496 ImplSourceFnPointer(d) => &d.nested[..],
497 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => &[],
498 ImplSourceTraitAlias(d) => &d.nested[..],
502 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
507 ImplSourceUserDefined(i) => ImplSourceUserDefined(ImplSourceUserDefinedData {
508 impl_def_id: i.impl_def_id,
510 nested: i.nested.into_iter().map(f).collect(),
512 ImplSourceParam(n) => ImplSourceParam(n.into_iter().map(f).collect()),
513 ImplSourceBuiltin(i) => ImplSourceBuiltin(ImplSourceBuiltinData {
514 nested: i.nested.into_iter().map(f).collect(),
516 ImplSourceObject(o) => ImplSourceObject(ImplSourceObjectData {
517 upcast_trait_ref: o.upcast_trait_ref,
518 vtable_base: o.vtable_base,
519 nested: o.nested.into_iter().map(f).collect(),
521 ImplSourceAutoImpl(d) => ImplSourceAutoImpl(ImplSourceAutoImplData {
522 trait_def_id: d.trait_def_id,
523 nested: d.nested.into_iter().map(f).collect(),
525 ImplSourceClosure(c) => ImplSourceClosure(ImplSourceClosureData {
526 closure_def_id: c.closure_def_id,
528 nested: c.nested.into_iter().map(f).collect(),
530 ImplSourceGenerator(c) => ImplSourceGenerator(ImplSourceGeneratorData {
531 generator_def_id: c.generator_def_id,
533 nested: c.nested.into_iter().map(f).collect(),
535 ImplSourceFnPointer(p) => ImplSourceFnPointer(ImplSourceFnPointerData {
537 nested: p.nested.into_iter().map(f).collect(),
539 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData) => {
540 ImplSourceDiscriminantKind(ImplSourceDiscriminantKindData)
542 ImplSourceTraitAlias(d) => ImplSourceTraitAlias(ImplSourceTraitAliasData {
543 alias_def_id: d.alias_def_id,
545 nested: d.nested.into_iter().map(f).collect(),
551 /// Identifies a particular impl in the source, along with a set of
552 /// substitutions from the impl's type/lifetime parameters. The
553 /// `nested` vector corresponds to the nested obligations attached to
554 /// the impl's type parameters.
556 /// The type parameter `N` indicates the type used for "nested
557 /// obligations" that are required by the impl. During type-check, this
558 /// is `Obligation`, as one might expect. During codegen, however, this
559 /// is `()`, because codegen only requires a shallow resolution of an
560 /// impl, and nested obligations are satisfied later.
561 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
562 pub struct ImplSourceUserDefinedData<'tcx, N> {
563 pub impl_def_id: DefId,
564 pub substs: SubstsRef<'tcx>,
568 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
569 pub struct ImplSourceGeneratorData<'tcx, N> {
570 pub generator_def_id: DefId,
571 pub substs: SubstsRef<'tcx>,
572 /// Nested obligations. This can be non-empty if the generator
573 /// signature contains associated types.
577 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
578 pub struct ImplSourceClosureData<'tcx, N> {
579 pub closure_def_id: DefId,
580 pub substs: SubstsRef<'tcx>,
581 /// Nested obligations. This can be non-empty if the closure
582 /// signature contains associated types.
586 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
587 pub struct ImplSourceAutoImplData<N> {
588 pub trait_def_id: DefId,
592 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
593 pub struct ImplSourceBuiltinData<N> {
597 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
598 pub struct ImplSourceObjectData<'tcx, N> {
599 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
600 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
602 /// The vtable is formed by concatenating together the method lists of
603 /// the base object trait and all supertraits; this is the start of
604 /// `upcast_trait_ref`'s methods in that vtable.
605 pub vtable_base: usize,
610 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
611 pub struct ImplSourceFnPointerData<'tcx, N> {
616 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
617 #[derive(Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
618 pub struct ImplSourceDiscriminantKindData;
620 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable, TypeFoldable)]
621 pub struct ImplSourceTraitAliasData<'tcx, N> {
622 pub alias_def_id: DefId,
623 pub substs: SubstsRef<'tcx>,
627 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable)]
628 pub enum ObjectSafetyViolation {
629 /// `Self: Sized` declared on the trait.
630 SizedSelf(SmallVec<[Span; 1]>),
632 /// Supertrait reference references `Self` an in illegal location
633 /// (e.g., `trait Foo : Bar<Self>`).
634 SupertraitSelf(SmallVec<[Span; 1]>),
636 /// Method has something illegal.
637 Method(Symbol, MethodViolationCode, Span),
639 /// Associated const.
640 AssocConst(Symbol, Span),
643 impl ObjectSafetyViolation {
644 pub fn error_msg(&self) -> Cow<'static, str> {
646 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
647 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
648 if spans.iter().any(|sp| *sp != DUMMY_SP) {
649 "it uses `Self` as a type parameter in this".into()
651 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
655 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
656 format!("associated function `{}` has no `self` parameter", name).into()
658 ObjectSafetyViolation::Method(
660 MethodViolationCode::ReferencesSelfInput(_),
662 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
663 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
664 format!("method `{}` references the `Self` type in this parameter", name).into()
666 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
667 format!("method `{}` references the `Self` type in its return type", name).into()
669 ObjectSafetyViolation::Method(
671 MethodViolationCode::WhereClauseReferencesSelf,
674 format!("method `{}` references the `Self` type in its `where` clause", name).into()
676 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
677 format!("method `{}` has generic type parameters", name).into()
679 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
680 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
682 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
683 format!("it contains associated `const` `{}`", name).into()
685 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
689 pub fn solution(&self) -> Option<(String, Option<(String, Span)>)> {
691 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {
694 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(sugg), _) => (
696 "consider turning `{}` into a method by giving it a `&self` argument or \
697 constraining it so it does not apply to trait objects",
700 sugg.map(|(sugg, sp)| (sugg.to_string(), sp)),
702 ObjectSafetyViolation::Method(
704 MethodViolationCode::UndispatchableReceiver,
707 format!("consider changing method `{}`'s `self` parameter to be `&self`", name),
708 Some(("&Self".to_string(), span)),
710 ObjectSafetyViolation::AssocConst(name, _)
711 | ObjectSafetyViolation::Method(name, ..) => {
712 (format!("consider moving `{}` to another trait", name), None)
717 pub fn spans(&self) -> SmallVec<[Span; 1]> {
718 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
719 // diagnostics use a `note` instead of a `span_label`.
721 ObjectSafetyViolation::SupertraitSelf(spans)
722 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
723 ObjectSafetyViolation::AssocConst(_, span)
724 | ObjectSafetyViolation::Method(_, _, span)
725 if *span != DUMMY_SP =>
734 /// Reasons a method might not be object-safe.
735 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
736 pub enum MethodViolationCode {
738 StaticMethod(Option<(&'static str, Span)>),
740 /// e.g., `fn foo(&self, x: Self)`
741 ReferencesSelfInput(usize),
743 /// e.g., `fn foo(&self) -> Self`
744 ReferencesSelfOutput,
746 /// e.g., `fn foo(&self) where Self: Clone`
747 WhereClauseReferencesSelf,
749 /// e.g., `fn foo<A>()`
752 /// the method's receiver (`self` argument) can't be dispatched on
753 UndispatchableReceiver,