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::thir::abstract_const::NotConstEvaluatable;
14 use crate::ty::subst::SubstsRef;
15 use crate::ty::{self, AdtKind, Ty, TyCtxt};
17 use rustc_data_structures::sync::Lrc;
18 use rustc_errors::{Applicability, Diagnostic};
20 use rustc_hir::def_id::{DefId, LocalDefId};
21 use rustc_span::symbol::Symbol;
22 use rustc_span::{Span, DUMMY_SP};
23 use smallvec::SmallVec;
26 use std::hash::{Hash, Hasher};
28 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
30 pub type CanonicalChalkEnvironmentAndGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>;
32 pub use self::ObligationCauseCode::*;
34 pub use self::chalk::{ChalkEnvironmentAndGoal, RustInterner as ChalkRustInterner};
36 /// Depending on the stage of compilation, we want projection to be
37 /// more or less conservative.
38 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
40 /// At type-checking time, we refuse to project any associated
41 /// type that is marked `default`. Non-`default` ("final") types
42 /// are always projected. This is necessary in general for
43 /// soundness of specialization. However, we *could* allow
44 /// projections in fully-monomorphic cases. We choose not to,
45 /// because we prefer for `default type` to force the type
46 /// definition to be treated abstractly by any consumers of the
47 /// impl. Concretely, that means that the following example will
55 /// impl<T> Assoc for T {
56 /// default type Output = bool;
60 /// let <() as Assoc>::Output = true;
65 /// At codegen time, all monomorphic projections will succeed.
66 /// Also, `impl Trait` is normalized to the concrete type,
67 /// which has to be already collected by type-checking.
69 /// NOTE: as `impl Trait`'s concrete type should *never*
70 /// be observable directly by the user, `Reveal::All`
71 /// should not be used by checks which may expose
72 /// type equality or type contents to the user.
73 /// There are some exceptions, e.g., around auto traits and
74 /// transmute-checking, which expose some details, but
75 /// not the whole concrete type of the `impl Trait`.
79 /// The reason why we incurred this obligation; used for error reporting.
81 /// Non-misc `ObligationCauseCode`s are stored on the heap. This gives the
82 /// best trade-off between keeping the type small (which makes copies cheaper)
83 /// while not doing too many heap allocations.
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, Debug, PartialEq, Eq, Lift)]
88 pub struct ObligationCause<'tcx> {
91 /// The ID of the fn body that triggered this obligation. This is
92 /// used for region obligations to determine the precise
93 /// environment in which the region obligation should be evaluated
94 /// (in particular, closures can add new assumptions). See the
95 /// field `region_obligations` of the `FulfillmentContext` for more
97 pub body_id: hir::HirId,
99 /// `None` for `MISC_OBLIGATION_CAUSE_CODE` (a common case, occurs ~60% of
100 /// the time). `Some` otherwise.
101 code: Option<Lrc<ObligationCauseCode<'tcx>>>,
104 // This custom hash function speeds up hashing for `Obligation` deduplication
105 // greatly by skipping the `code` field, which can be large and complex. That
106 // shouldn't affect hash quality much since there are several other fields in
107 // `Obligation` which should be unique enough, especially the predicate itself
108 // which is hashed as an interned pointer. See #90996.
109 impl Hash for ObligationCause<'_> {
110 fn hash<H: Hasher>(&self, state: &mut H) {
111 self.body_id.hash(state);
112 self.span.hash(state);
116 const MISC_OBLIGATION_CAUSE_CODE: ObligationCauseCode<'static> = MiscObligation;
118 impl<'tcx> ObligationCause<'tcx> {
123 code: ObligationCauseCode<'tcx>,
124 ) -> ObligationCause<'tcx> {
128 code: if code == MISC_OBLIGATION_CAUSE_CODE { None } else { Some(Lrc::new(code)) },
132 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
133 ObligationCause::new(span, body_id, MiscObligation)
137 pub fn dummy() -> ObligationCause<'tcx> {
138 ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: None }
141 pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> {
142 ObligationCause { span, body_id: hir::CRATE_HIR_ID, code: None }
145 pub fn make_mut_code(&mut self) -> &mut ObligationCauseCode<'tcx> {
146 Lrc::make_mut(self.code.get_or_insert_with(|| Lrc::new(MISC_OBLIGATION_CAUSE_CODE)))
149 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
151 ObligationCauseCode::CompareImplMethodObligation { .. }
152 | ObligationCauseCode::MainFunctionType
153 | ObligationCauseCode::StartFunctionType => {
154 tcx.sess.source_map().guess_head_span(self.span)
156 ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
165 pub fn code(&self) -> &ObligationCauseCode<'tcx> {
166 self.code.as_deref().unwrap_or(&MISC_OBLIGATION_CAUSE_CODE)
169 pub fn clone_code(&self) -> Lrc<ObligationCauseCode<'tcx>> {
171 Some(code) => code.clone(),
172 None => Lrc::new(MISC_OBLIGATION_CAUSE_CODE),
177 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
178 pub struct UnifyReceiverContext<'tcx> {
179 pub assoc_item: ty::AssocItem,
180 pub param_env: ty::ParamEnv<'tcx>,
181 pub substs: SubstsRef<'tcx>,
184 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
185 pub enum ObligationCauseCode<'tcx> {
186 /// Not well classified or should be obvious from the span.
189 /// A slice or array is WF only if `T: Sized`.
192 /// A tuple is WF only if its middle elements are `Sized`.
195 /// This is the trait reference from the given projection.
196 ProjectionWf(ty::ProjectionTy<'tcx>),
198 /// In an impl of trait `X` for type `Y`, type `Y` must
199 /// also implement all supertraits of `X`.
200 ItemObligation(DefId),
202 /// Like `ItemObligation`, but with extra detail on the source of the obligation.
203 BindingObligation(DefId, Span),
205 /// A type like `&'a T` is WF only if `T: 'a`.
206 ReferenceOutlivesReferent(Ty<'tcx>),
208 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
209 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
211 /// Obligation incurred due to an object cast.
212 ObjectCastObligation(/* Object type */ Ty<'tcx>),
214 /// Obligation incurred due to a coercion.
220 /// Various cases where expressions must be `Sized` / `Copy` / etc.
221 /// `L = X` implies that `L` is `Sized`.
223 /// `(x1, .., xn)` must be `Sized`.
224 TupleInitializerSized,
225 /// `S { ... }` must be `Sized`.
226 StructInitializerSized,
227 /// Type of each variable must be `Sized`.
228 VariableType(hir::HirId),
229 /// Argument type must be `Sized`.
230 SizedArgumentType(Option<Span>),
231 /// Return type must be `Sized`.
233 /// Yield type must be `Sized`.
235 /// Box expression result type must be `Sized`.
237 /// Inline asm operand type must be `Sized`.
239 /// `[T, ..n]` implies that `T` must be `Copy`.
240 /// If the function in the array repeat expression is a `const fn`,
241 /// display a help message suggesting to move the function call to a
242 /// new `const` item while saying that `T` doesn't implement `Copy`.
245 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
252 /// Constant expressions must be sized.
255 /// `static` items must have `Sync` type.
258 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
260 ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>),
262 DerivedObligation(DerivedObligationCause<'tcx>),
264 FunctionArgumentObligation {
265 /// The node of the relevant argument in the function call.
266 arg_hir_id: hir::HirId,
267 /// The node of the function call.
268 call_hir_id: hir::HirId,
269 /// The obligation introduced by this argument.
270 parent_code: Lrc<ObligationCauseCode<'tcx>>,
273 /// Error derived when matching traits/impls; see ObligationCause for more details
274 CompareImplConstObligation,
276 /// Error derived when matching traits/impls; see ObligationCause for more details
277 CompareImplMethodObligation {
278 impl_item_def_id: DefId,
279 trait_item_def_id: DefId,
282 /// Error derived when matching traits/impls; see ObligationCause for more details
283 CompareImplTypeObligation {
284 impl_item_def_id: DefId,
285 trait_item_def_id: DefId,
288 /// Checking that the bounds of a trait's associated type hold for a given impl
289 CheckAssociatedTypeBounds {
290 impl_item_def_id: DefId,
291 trait_item_def_id: DefId,
294 /// Checking that this expression can be assigned where it needs to be
295 // FIXME(eddyb) #11161 is the original Expr required?
298 /// Computing common supertype in the arms of a match expression
299 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
301 /// Type error arising from type checking a pattern against an expected type.
303 /// The span of the scrutinee or type expression which caused the `root_ty` type.
305 /// The root expected type induced by a scrutinee or type expression.
307 /// Whether the `Span` came from an expression or a type expression.
311 /// Constants in patterns must have `Structural` type.
312 ConstPatternStructural,
314 /// Computing common supertype in an if expression
315 IfExpression(Box<IfExpressionCause>),
317 /// Computing common supertype of an if expression with no else counter-part
318 IfExpressionWithNoElse,
320 /// `main` has wrong type
323 /// `start` has wrong type
326 /// Intrinsic has wrong type
329 /// A let else block does not diverge
335 UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
337 /// `return` with no expression
340 /// `return` with an expression
341 ReturnValue(hir::HirId),
343 /// Return type of this function
346 /// Block implicit return
347 BlockTailExpression(hir::HirId),
349 /// #[feature(trivial_bounds)] is not enabled
352 /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
355 AwaitableExpr(Option<hir::HirId>),
361 /// Well-formed checking. If a `WellFormedLoc` is provided,
362 /// then it will be used to eprform HIR-based wf checking
363 /// after an error occurs, in order to generate a more precise error span.
364 /// This is purely for diagnostic purposes - it is always
365 /// correct to use `MiscObligation` instead, or to specify
366 /// `WellFormed(None)`
367 WellFormed(Option<WellFormedLoc>),
369 /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against.
370 MatchImpl(ObligationCause<'tcx>, DefId),
373 rhs_span: Option<Span>,
378 /// The 'location' at which we try to perform HIR-based wf checking.
379 /// This information is used to obtain an `hir::Ty`, which
380 /// we can walk in order to obtain precise spans for any
381 /// 'nested' types (e.g. `Foo` in `Option<Foo>`).
382 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
383 pub enum WellFormedLoc {
384 /// Use the type of the provided definition.
386 /// Use the type of the parameter of the provided function.
387 /// We cannot use `hir::Param`, since the function may
388 /// not have a body (e.g. a trait method definition)
390 /// The function to lookup the parameter in
391 function: LocalDefId,
392 /// The index of the parameter to use.
393 /// Parameters are indexed from 0, with the return type
394 /// being the last 'parameter'
399 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
400 pub struct ImplDerivedObligationCause<'tcx> {
401 pub derived: DerivedObligationCause<'tcx>,
402 pub impl_def_id: DefId,
406 impl ObligationCauseCode<'_> {
407 // Return the base obligation, ignoring derived obligations.
408 pub fn peel_derives(&self) -> &Self {
409 let mut base_cause = self;
412 BuiltinDerivedObligation(DerivedObligationCause { parent_code, .. })
413 | DerivedObligation(DerivedObligationCause { parent_code, .. })
414 | FunctionArgumentObligation { parent_code, .. } => {
415 base_cause = &parent_code;
417 ImplDerivedObligation(obligation_cause) => {
418 base_cause = &*obligation_cause.derived.parent_code;
427 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
428 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
429 static_assert_size!(ObligationCauseCode<'_>, 48);
431 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
432 pub enum StatementAsExpression {
437 impl<'tcx> ty::Lift<'tcx> for StatementAsExpression {
438 type Lifted = StatementAsExpression;
439 fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> {
444 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
445 pub struct MatchExpressionArmCause<'tcx> {
447 pub scrut_span: Span,
448 pub semi_span: Option<(Span, StatementAsExpression)>,
449 pub source: hir::MatchSource,
450 pub prior_arms: Vec<Span>,
451 pub last_ty: Ty<'tcx>,
452 pub scrut_hir_id: hir::HirId,
453 pub opt_suggest_box_span: Option<Span>,
456 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
457 pub struct IfExpressionCause {
460 pub outer: Option<Span>,
461 pub semicolon: Option<(Span, StatementAsExpression)>,
462 pub opt_suggest_box_span: Option<Span>,
465 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
466 pub struct DerivedObligationCause<'tcx> {
467 /// The trait predicate of the parent obligation that led to the
468 /// current obligation. Note that only trait obligations lead to
469 /// derived obligations, so we just store the trait predicate here
471 pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
473 /// The parent trait had this cause.
474 pub parent_code: Lrc<ObligationCauseCode<'tcx>>,
477 #[derive(Clone, Debug, TypeFoldable, Lift)]
478 pub enum SelectionError<'tcx> {
479 /// The trait is not implemented.
481 /// After a closure impl has selected, its "outputs" were evaluated
482 /// (which for closures includes the "input" type params) and they
483 /// didn't resolve. See `confirm_poly_trait_refs` for more.
484 OutputTypeParameterMismatch(
485 ty::PolyTraitRef<'tcx>,
486 ty::PolyTraitRef<'tcx>,
487 ty::error::TypeError<'tcx>,
489 /// The trait pointed by `DefId` is not object safe.
490 TraitNotObjectSafe(DefId),
491 /// A given constant couldn't be evaluated.
492 NotConstEvaluatable(NotConstEvaluatable),
493 /// Exceeded the recursion depth during type projection.
494 Overflow(OverflowError),
495 /// Signaling that an error has already been emitted, to avoid
496 /// multiple errors being shown.
498 /// Multiple applicable `impl`s where found. The `DefId`s correspond to
499 /// all the `impl`s' Items.
500 Ambiguous(Vec<DefId>),
503 /// When performing resolution, it is typically the case that there
504 /// can be one of three outcomes:
506 /// - `Ok(Some(r))`: success occurred with result `r`
507 /// - `Ok(None)`: could not definitely determine anything, usually due
508 /// to inconclusive type inference.
509 /// - `Err(e)`: error `e` occurred
510 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
512 /// Given the successful resolution of an obligation, the `ImplSource`
513 /// indicates where the impl comes from.
515 /// For example, the obligation may be satisfied by a specific impl (case A),
516 /// or it may be relative to some bound that is in scope (case B).
519 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
520 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
521 /// impl Clone for i32 { ... } // Impl_3
523 /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) {
524 /// // Case A: ImplSource points at a specific impl. Only possible when
525 /// // type is concretely known. If the impl itself has bounded
526 /// // type parameters, ImplSource will carry resolutions for those as well:
527 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
529 /// // Case A: ImplSource points at a specific impl. Only possible when
530 /// // type is concretely known. If the impl itself has bounded
531 /// // type parameters, ImplSource will carry resolutions for those as well:
532 /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])])
534 /// // Case B: ImplSource must be provided by caller. This applies when
535 /// // type is a type parameter.
536 /// param.clone(); // ImplSource::Param
538 /// // Case C: A mix of cases A and B.
539 /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param])
543 /// ### The type parameter `N`
545 /// See explanation on `ImplSourceUserDefinedData`.
546 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
547 pub enum ImplSource<'tcx, N> {
548 /// ImplSource identifying a particular impl.
549 UserDefined(ImplSourceUserDefinedData<'tcx, N>),
551 /// ImplSource for auto trait implementations.
552 /// This carries the information and nested obligations with regards
553 /// to an auto implementation for a trait `Trait`. The nested obligations
554 /// ensure the trait implementation holds for all the constituent types.
555 AutoImpl(ImplSourceAutoImplData<N>),
557 /// Successful resolution to an obligation provided by the caller
558 /// for some type parameter. The `Vec<N>` represents the
559 /// obligations incurred from normalizing the where-clause (if
561 Param(Vec<N>, ty::BoundConstness),
563 /// Virtual calls through an object.
564 Object(ImplSourceObjectData<'tcx, N>),
566 /// Successful resolution for a builtin trait.
567 Builtin(ImplSourceBuiltinData<N>),
569 /// ImplSource for trait upcasting coercion
570 TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>),
572 /// ImplSource automatically generated for a closure. The `DefId` is the ID
573 /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the
574 /// impl is generated by the compiler and does not appear in the source.
575 Closure(ImplSourceClosureData<'tcx, N>),
577 /// Same as above, but for a function pointer type with the given signature.
578 FnPointer(ImplSourceFnPointerData<'tcx, N>),
580 /// ImplSource for a builtin `DeterminantKind` trait implementation.
581 DiscriminantKind(ImplSourceDiscriminantKindData),
583 /// ImplSource for a builtin `Pointee` trait implementation.
584 Pointee(ImplSourcePointeeData),
586 /// ImplSource automatically generated for a generator.
587 Generator(ImplSourceGeneratorData<'tcx, N>),
589 /// ImplSource for a trait alias.
590 TraitAlias(ImplSourceTraitAliasData<'tcx, N>),
592 /// ImplSource for a `const Drop` implementation.
593 ConstDestruct(ImplSourceConstDestructData<N>),
596 impl<'tcx, N> ImplSource<'tcx, N> {
597 pub fn nested_obligations(self) -> Vec<N> {
599 ImplSource::UserDefined(i) => i.nested,
600 ImplSource::Param(n, _) => n,
601 ImplSource::Builtin(i) => i.nested,
602 ImplSource::AutoImpl(d) => d.nested,
603 ImplSource::Closure(c) => c.nested,
604 ImplSource::Generator(c) => c.nested,
605 ImplSource::Object(d) => d.nested,
606 ImplSource::FnPointer(d) => d.nested,
607 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
608 | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(),
609 ImplSource::TraitAlias(d) => d.nested,
610 ImplSource::TraitUpcasting(d) => d.nested,
611 ImplSource::ConstDestruct(i) => i.nested,
615 pub fn borrow_nested_obligations(&self) -> &[N] {
617 ImplSource::UserDefined(i) => &i.nested[..],
618 ImplSource::Param(n, _) => &n,
619 ImplSource::Builtin(i) => &i.nested,
620 ImplSource::AutoImpl(d) => &d.nested,
621 ImplSource::Closure(c) => &c.nested,
622 ImplSource::Generator(c) => &c.nested,
623 ImplSource::Object(d) => &d.nested,
624 ImplSource::FnPointer(d) => &d.nested,
625 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
626 | ImplSource::Pointee(ImplSourcePointeeData) => &[],
627 ImplSource::TraitAlias(d) => &d.nested,
628 ImplSource::TraitUpcasting(d) => &d.nested,
629 ImplSource::ConstDestruct(i) => &i.nested,
633 pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M>
638 ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData {
639 impl_def_id: i.impl_def_id,
641 nested: i.nested.into_iter().map(f).collect(),
643 ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct),
644 ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData {
645 nested: i.nested.into_iter().map(f).collect(),
647 ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData {
648 upcast_trait_ref: o.upcast_trait_ref,
649 vtable_base: o.vtable_base,
650 nested: o.nested.into_iter().map(f).collect(),
652 ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData {
653 trait_def_id: d.trait_def_id,
654 nested: d.nested.into_iter().map(f).collect(),
656 ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData {
657 closure_def_id: c.closure_def_id,
659 nested: c.nested.into_iter().map(f).collect(),
661 ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData {
662 generator_def_id: c.generator_def_id,
664 nested: c.nested.into_iter().map(f).collect(),
666 ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData {
668 nested: p.nested.into_iter().map(f).collect(),
670 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => {
671 ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
673 ImplSource::Pointee(ImplSourcePointeeData) => {
674 ImplSource::Pointee(ImplSourcePointeeData)
676 ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData {
677 alias_def_id: d.alias_def_id,
679 nested: d.nested.into_iter().map(f).collect(),
681 ImplSource::TraitUpcasting(d) => {
682 ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData {
683 upcast_trait_ref: d.upcast_trait_ref,
684 vtable_vptr_slot: d.vtable_vptr_slot,
685 nested: d.nested.into_iter().map(f).collect(),
688 ImplSource::ConstDestruct(i) => {
689 ImplSource::ConstDestruct(ImplSourceConstDestructData {
690 nested: i.nested.into_iter().map(f).collect(),
697 /// Identifies a particular impl in the source, along with a set of
698 /// substitutions from the impl's type/lifetime parameters. The
699 /// `nested` vector corresponds to the nested obligations attached to
700 /// the impl's type parameters.
702 /// The type parameter `N` indicates the type used for "nested
703 /// obligations" that are required by the impl. During type-check, this
704 /// is `Obligation`, as one might expect. During codegen, however, this
705 /// is `()`, because codegen only requires a shallow resolution of an
706 /// impl, and nested obligations are satisfied later.
707 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
708 pub struct ImplSourceUserDefinedData<'tcx, N> {
709 pub impl_def_id: DefId,
710 pub substs: SubstsRef<'tcx>,
714 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
715 pub struct ImplSourceGeneratorData<'tcx, N> {
716 pub generator_def_id: DefId,
717 pub substs: SubstsRef<'tcx>,
718 /// Nested obligations. This can be non-empty if the generator
719 /// signature contains associated types.
723 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
724 pub struct ImplSourceClosureData<'tcx, N> {
725 pub closure_def_id: DefId,
726 pub substs: SubstsRef<'tcx>,
727 /// Nested obligations. This can be non-empty if the closure
728 /// signature contains associated types.
732 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
733 pub struct ImplSourceAutoImplData<N> {
734 pub trait_def_id: DefId,
738 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
739 pub struct ImplSourceTraitUpcastingData<'tcx, N> {
740 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
741 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
743 /// The vtable is formed by concatenating together the method lists of
744 /// the base object trait and all supertraits, pointers to supertrait vtable will
745 /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
746 /// within that vtable.
747 pub vtable_vptr_slot: Option<usize>,
752 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
753 pub struct ImplSourceBuiltinData<N> {
757 #[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
758 pub struct ImplSourceObjectData<'tcx, N> {
759 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
760 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
762 /// The vtable is formed by concatenating together the method lists of
763 /// the base object trait and all supertraits, pointers to supertrait vtable will
764 /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
766 pub vtable_base: usize,
771 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
772 pub struct ImplSourceFnPointerData<'tcx, N> {
777 // FIXME(@lcnr): This should be refactored and merged with other builtin vtables.
778 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
779 pub struct ImplSourceDiscriminantKindData;
781 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)]
782 pub struct ImplSourcePointeeData;
784 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
785 pub struct ImplSourceConstDestructData<N> {
789 #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, TypeFoldable, Lift)]
790 pub struct ImplSourceTraitAliasData<'tcx, N> {
791 pub alias_def_id: DefId,
792 pub substs: SubstsRef<'tcx>,
796 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
797 pub enum ObjectSafetyViolation {
798 /// `Self: Sized` declared on the trait.
799 SizedSelf(SmallVec<[Span; 1]>),
801 /// Supertrait reference references `Self` an in illegal location
802 /// (e.g., `trait Foo : Bar<Self>`).
803 SupertraitSelf(SmallVec<[Span; 1]>),
805 /// Method has something illegal.
806 Method(Symbol, MethodViolationCode, Span),
808 /// Associated const.
809 AssocConst(Symbol, Span),
815 impl ObjectSafetyViolation {
816 pub fn error_msg(&self) -> Cow<'static, str> {
818 ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
819 ObjectSafetyViolation::SupertraitSelf(ref spans) => {
820 if spans.iter().any(|sp| *sp != DUMMY_SP) {
821 "it uses `Self` as a type parameter".into()
823 "it cannot use `Self` as a type parameter in a supertrait or `where`-clause"
827 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_, _, _), _) => {
828 format!("associated function `{}` has no `self` parameter", name).into()
830 ObjectSafetyViolation::Method(
832 MethodViolationCode::ReferencesSelfInput(_),
834 ) => format!("method `{}` references the `Self` type in its parameters", name).into(),
835 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => {
836 format!("method `{}` references the `Self` type in this parameter", name).into()
838 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => {
839 format!("method `{}` references the `Self` type in its return type", name).into()
841 ObjectSafetyViolation::Method(
843 MethodViolationCode::WhereClauseReferencesSelf,
846 format!("method `{}` references the `Self` type in its `where` clause", name).into()
848 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
849 format!("method `{}` has generic type parameters", name).into()
851 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
852 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
854 ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => {
855 format!("it contains associated `const` `{}`", name).into()
857 ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(),
858 ObjectSafetyViolation::GAT(name, _) => {
859 format!("it contains the generic associated type `{}`", name).into()
864 pub fn solution(&self, err: &mut Diagnostic) {
866 ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {}
867 ObjectSafetyViolation::Method(
869 MethodViolationCode::StaticMethod(sugg, self_span, has_args),
875 "consider turning `{}` into a method by giving it a `&self` argument",
878 format!("&self{}", if has_args { ", " } else { "" }),
879 Applicability::MaybeIncorrect,
882 Some((sugg, span)) => {
886 "alternatively, consider constraining `{}` so it does not apply to \
891 Applicability::MaybeIncorrect,
896 "consider turning `{}` into a method by giving it a `&self` \
897 argument or constraining it so it does not apply to trait objects",
903 ObjectSafetyViolation::Method(
905 MethodViolationCode::UndispatchableReceiver,
911 "consider changing method `{}`'s `self` parameter to be `&self`",
915 Applicability::MachineApplicable,
918 ObjectSafetyViolation::AssocConst(name, _)
919 | ObjectSafetyViolation::GAT(name, _)
920 | ObjectSafetyViolation::Method(name, ..) => {
921 err.help(&format!("consider moving `{}` to another trait", name));
926 pub fn spans(&self) -> SmallVec<[Span; 1]> {
927 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
928 // diagnostics use a `note` instead of a `span_label`.
930 ObjectSafetyViolation::SupertraitSelf(spans)
931 | ObjectSafetyViolation::SizedSelf(spans) => spans.clone(),
932 ObjectSafetyViolation::AssocConst(_, span)
933 | ObjectSafetyViolation::GAT(_, span)
934 | ObjectSafetyViolation::Method(_, _, span)
935 if *span != DUMMY_SP =>
944 /// Reasons a method might not be object-safe.
945 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
946 pub enum MethodViolationCode {
948 StaticMethod(Option<(&'static str, Span)>, Span, bool /* has args */),
950 /// e.g., `fn foo(&self, x: Self)`
951 ReferencesSelfInput(usize),
953 /// e.g., `fn foo(&self) -> Self`
954 ReferencesSelfOutput,
956 /// e.g., `fn foo(&self) where Self: Clone`
957 WhereClauseReferencesSelf,
959 /// e.g., `fn foo<A>()`
962 /// the method's receiver (`self` argument) can't be dispatched on
963 UndispatchableReceiver,