| //! Trait Resolution. See the [rustc dev guide] for more information on how this works. |
| //! |
| //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html |
| |
| pub mod query; |
| pub mod select; |
| pub mod solve; |
| pub mod specialization_graph; |
| mod structural_impls; |
| pub mod util; |
| |
| use crate::infer::canonical::Canonical; |
| use crate::mir::ConstraintCategory; |
| use crate::ty::abstract_const::NotConstEvaluatable; |
| use crate::ty::GenericArgsRef; |
| use crate::ty::{self, AdtKind, Ty}; |
| |
| use rustc_data_structures::sync::Lrc; |
| use rustc_errors::{Applicability, Diag, EmissionGuarantee}; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::HirId; |
| use rustc_macros::{ |
| Decodable, Encodable, HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable, |
| }; |
| use rustc_span::def_id::{LocalDefId, CRATE_DEF_ID}; |
| use rustc_span::symbol::Symbol; |
| use rustc_span::{Span, DUMMY_SP}; |
| use smallvec::{smallvec, SmallVec}; |
| |
| use std::borrow::Cow; |
| use std::hash::{Hash, Hasher}; |
| |
| pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache}; |
| |
| pub use self::ObligationCauseCode::*; |
| |
| /// Depending on the stage of compilation, we want projection to be |
| /// more or less conservative. |
| #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable, Encodable, Decodable)] |
| pub enum Reveal { |
| /// At type-checking time, we refuse to project any associated |
| /// type that is marked `default`. Non-`default` ("final") types |
| /// are always projected. This is necessary in general for |
| /// soundness of specialization. However, we *could* allow |
| /// projections in fully-monomorphic cases. We choose not to, |
| /// because we prefer for `default type` to force the type |
| /// definition to be treated abstractly by any consumers of the |
| /// impl. Concretely, that means that the following example will |
| /// fail to compile: |
| /// |
| /// ```compile_fail,E0308 |
| /// #![feature(specialization)] |
| /// trait Assoc { |
| /// type Output; |
| /// } |
| /// |
| /// impl<T> Assoc for T { |
| /// default type Output = bool; |
| /// } |
| /// |
| /// fn main() { |
| /// let x: <() as Assoc>::Output = true; |
| /// } |
| /// ``` |
| /// |
| /// We also do not reveal the hidden type of opaque types during |
| /// type-checking. |
| UserFacing, |
| |
| /// At codegen time, all monomorphic projections will succeed. |
| /// Also, `impl Trait` is normalized to the concrete type, |
| /// which has to be already collected by type-checking. |
| /// |
| /// NOTE: as `impl Trait`'s concrete type should *never* |
| /// be observable directly by the user, `Reveal::All` |
| /// should not be used by checks which may expose |
| /// type equality or type contents to the user. |
| /// There are some exceptions, e.g., around auto traits and |
| /// transmute-checking, which expose some details, but |
| /// not the whole concrete type of the `impl Trait`. |
| All, |
| } |
| |
| /// The reason why we incurred this obligation; used for error reporting. |
| /// |
| /// Non-misc `ObligationCauseCode`s are stored on the heap. This gives the |
| /// best trade-off between keeping the type small (which makes copies cheaper) |
| /// while not doing too many heap allocations. |
| /// |
| /// We do not want to intern this as there are a lot of obligation causes which |
| /// only live for a short period of time. |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub struct ObligationCause<'tcx> { |
| pub span: Span, |
| |
| /// The ID of the fn body that triggered this obligation. This is |
| /// used for region obligations to determine the precise |
| /// environment in which the region obligation should be evaluated |
| /// (in particular, closures can add new assumptions). See the |
| /// field `region_obligations` of the `FulfillmentContext` for more |
| /// information. |
| pub body_id: LocalDefId, |
| |
| code: InternedObligationCauseCode<'tcx>, |
| } |
| |
| // This custom hash function speeds up hashing for `Obligation` deduplication |
| // greatly by skipping the `code` field, which can be large and complex. That |
| // shouldn't affect hash quality much since there are several other fields in |
| // `Obligation` which should be unique enough, especially the predicate itself |
| // which is hashed as an interned pointer. See #90996. |
| impl Hash for ObligationCause<'_> { |
| fn hash<H: Hasher>(&self, state: &mut H) { |
| self.body_id.hash(state); |
| self.span.hash(state); |
| } |
| } |
| |
| impl<'tcx> ObligationCause<'tcx> { |
| #[inline] |
| pub fn new( |
| span: Span, |
| body_id: LocalDefId, |
| code: ObligationCauseCode<'tcx>, |
| ) -> ObligationCause<'tcx> { |
| ObligationCause { span, body_id, code: code.into() } |
| } |
| |
| pub fn misc(span: Span, body_id: LocalDefId) -> ObligationCause<'tcx> { |
| ObligationCause::new(span, body_id, MiscObligation) |
| } |
| |
| #[inline(always)] |
| pub fn dummy() -> ObligationCause<'tcx> { |
| ObligationCause::dummy_with_span(DUMMY_SP) |
| } |
| |
| #[inline(always)] |
| pub fn dummy_with_span(span: Span) -> ObligationCause<'tcx> { |
| ObligationCause { span, body_id: CRATE_DEF_ID, code: Default::default() } |
| } |
| |
| pub fn span(&self) -> Span { |
| match *self.code() { |
| ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause { |
| arm_span, |
| .. |
| }) => arm_span, |
| _ => self.span, |
| } |
| } |
| |
| #[inline] |
| pub fn code(&self) -> &ObligationCauseCode<'tcx> { |
| &self.code |
| } |
| |
| pub fn map_code( |
| &mut self, |
| f: impl FnOnce(InternedObligationCauseCode<'tcx>) -> ObligationCauseCode<'tcx>, |
| ) { |
| self.code = f(std::mem::take(&mut self.code)).into(); |
| } |
| |
| pub fn derived_cause( |
| mut self, |
| parent_trait_pred: ty::PolyTraitPredicate<'tcx>, |
| variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>, |
| ) -> ObligationCause<'tcx> { |
| /*! |
| * Creates a cause for obligations that are derived from |
| * `obligation` by a recursive search (e.g., for a builtin |
| * bound, or eventually a `auto trait Foo`). If `obligation` |
| * is itself a derived obligation, this is just a clone, but |
| * otherwise we create a "derived obligation" cause so as to |
| * keep track of the original root obligation for error |
| * reporting. |
| */ |
| |
| // NOTE(flaper87): As of now, it keeps track of the whole error |
| // chain. Ideally, we should have a way to configure this either |
| // by using -Z verbose-internals or just a CLI argument. |
| self.code = |
| variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into(); |
| self |
| } |
| |
| pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> { |
| match self.code() { |
| MatchImpl(cause, _) => cause.to_constraint_category(), |
| AscribeUserTypeProvePredicate(predicate_span) => { |
| ConstraintCategory::Predicate(*predicate_span) |
| } |
| _ => ConstraintCategory::BoringNoLocation, |
| } |
| } |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub struct UnifyReceiverContext<'tcx> { |
| pub assoc_item: ty::AssocItem, |
| pub param_env: ty::ParamEnv<'tcx>, |
| pub args: GenericArgsRef<'tcx>, |
| } |
| |
| #[derive(Clone, PartialEq, Eq, Default, HashStable)] |
| #[derive(TypeVisitable, TypeFoldable, TyEncodable, TyDecodable)] |
| pub struct InternedObligationCauseCode<'tcx> { |
| /// `None` for `ObligationCauseCode::MiscObligation` (a common case, occurs ~60% of |
| /// the time). `Some` otherwise. |
| code: Option<Lrc<ObligationCauseCode<'tcx>>>, |
| } |
| |
| impl<'tcx> std::fmt::Debug for InternedObligationCauseCode<'tcx> { |
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
| let cause: &ObligationCauseCode<'_> = self; |
| cause.fmt(f) |
| } |
| } |
| |
| impl<'tcx> ObligationCauseCode<'tcx> { |
| #[inline(always)] |
| fn into(self) -> InternedObligationCauseCode<'tcx> { |
| InternedObligationCauseCode { |
| code: if let ObligationCauseCode::MiscObligation = self { |
| None |
| } else { |
| Some(Lrc::new(self)) |
| }, |
| } |
| } |
| } |
| |
| impl<'tcx> std::ops::Deref for InternedObligationCauseCode<'tcx> { |
| type Target = ObligationCauseCode<'tcx>; |
| |
| fn deref(&self) -> &Self::Target { |
| self.code.as_deref().unwrap_or(&ObligationCauseCode::MiscObligation) |
| } |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub enum ObligationCauseCode<'tcx> { |
| /// Not well classified or should be obvious from the span. |
| MiscObligation, |
| |
| /// A slice or array is WF only if `T: Sized`. |
| SliceOrArrayElem, |
| |
| /// A tuple is WF only if its middle elements are `Sized`. |
| TupleElem, |
| |
| /// Must satisfy all of the where-clause predicates of the |
| /// given item. |
| ItemObligation(DefId), |
| |
| /// Like `ItemObligation`, but carries the span of the |
| /// predicate when it can be identified. |
| BindingObligation(DefId, Span), |
| |
| /// Like `ItemObligation`, but carries the `HirId` of the |
| /// expression that caused the obligation, and the `usize` |
| /// indicates exactly which predicate it is in the list of |
| /// instantiated predicates. |
| ExprItemObligation(DefId, HirId, usize), |
| |
| /// Combines `ExprItemObligation` and `BindingObligation`. |
| ExprBindingObligation(DefId, Span, HirId, usize), |
| |
| /// A type like `&'a T` is WF only if `T: 'a`. |
| ReferenceOutlivesReferent(Ty<'tcx>), |
| |
| /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`. |
| ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>), |
| |
| /// Obligation incurred due to a coercion. |
| Coercion { |
| source: Ty<'tcx>, |
| target: Ty<'tcx>, |
| }, |
| |
| /// Various cases where expressions must be `Sized` / `Copy` / etc. |
| /// `L = X` implies that `L` is `Sized`. |
| AssignmentLhsSized, |
| /// `(x1, .., xn)` must be `Sized`. |
| TupleInitializerSized, |
| /// `S { ... }` must be `Sized`. |
| StructInitializerSized, |
| /// Type of each variable must be `Sized`. |
| VariableType(HirId), |
| /// Argument type must be `Sized`. |
| SizedArgumentType(Option<HirId>), |
| /// Return type must be `Sized`. |
| SizedReturnType, |
| /// Return type of a call expression must be `Sized`. |
| SizedCallReturnType, |
| /// Yield type must be `Sized`. |
| SizedYieldType, |
| /// Inline asm operand type must be `Sized`. |
| InlineAsmSized, |
| /// Captured closure type must be `Sized`. |
| SizedClosureCapture(LocalDefId), |
| /// Types live across coroutine yields must be `Sized`. |
| SizedCoroutineInterior(LocalDefId), |
| /// `[expr; N]` requires `type_of(expr): Copy`. |
| RepeatElementCopy { |
| /// If element is a `const fn` or const ctor we display a help message suggesting |
| /// to move it to a new `const` item while saying that `T` doesn't implement `Copy`. |
| is_constable: IsConstable, |
| elt_type: Ty<'tcx>, |
| elt_span: Span, |
| /// Span of the statement/item in which the repeat expression occurs. We can use this to |
| /// place a `const` declaration before it |
| elt_stmt_span: Span, |
| }, |
| |
| /// Types of fields (other than the last, except for packed structs) in a struct must be sized. |
| FieldSized { |
| adt_kind: AdtKind, |
| span: Span, |
| last: bool, |
| }, |
| |
| /// Constant expressions must be sized. |
| ConstSized, |
| |
| /// `static` items must have `Sync` type. |
| SharedStatic, |
| |
| /// Derived obligation (i.e. theoretical `where` clause) on a built-in |
| /// implementation like `Copy` or `Sized`. |
| BuiltinDerivedObligation(DerivedObligationCause<'tcx>), |
| |
| /// Derived obligation (i.e. `where` clause) on an user-provided impl |
| /// or a trait alias. |
| ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>), |
| |
| /// Derived obligation for WF goals. |
| WellFormedDerivedObligation(DerivedObligationCause<'tcx>), |
| |
| FunctionArgumentObligation { |
| /// The node of the relevant argument in the function call. |
| arg_hir_id: HirId, |
| /// The node of the function call. |
| call_hir_id: HirId, |
| /// The obligation introduced by this argument. |
| parent_code: InternedObligationCauseCode<'tcx>, |
| }, |
| |
| /// Error derived when checking an impl item is compatible with |
| /// its corresponding trait item's definition |
| CompareImplItemObligation { |
| impl_item_def_id: LocalDefId, |
| trait_item_def_id: DefId, |
| kind: ty::AssocKind, |
| }, |
| |
| /// Checking that the bounds of a trait's associated type hold for a given impl |
| CheckAssociatedTypeBounds { |
| impl_item_def_id: LocalDefId, |
| trait_item_def_id: DefId, |
| }, |
| |
| /// Checking that this expression can be assigned to its target. |
| ExprAssignable, |
| |
| /// Computing common supertype in the arms of a match expression |
| MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>), |
| |
| /// Type error arising from type checking a pattern against an expected type. |
| Pattern { |
| /// The span of the scrutinee or type expression which caused the `root_ty` type. |
| span: Option<Span>, |
| /// The root expected type induced by a scrutinee or type expression. |
| root_ty: Ty<'tcx>, |
| /// Whether the `Span` came from an expression or a type expression. |
| origin_expr: bool, |
| }, |
| |
| /// Computing common supertype in an if expression |
| IfExpression(Box<IfExpressionCause<'tcx>>), |
| |
| /// Computing common supertype of an if expression with no else counter-part |
| IfExpressionWithNoElse, |
| |
| /// `main` has wrong type |
| MainFunctionType, |
| |
| /// `start` has wrong type |
| StartFunctionType, |
| |
| /// language function has wrong type |
| LangFunctionType(Symbol), |
| |
| /// Intrinsic has wrong type |
| IntrinsicType, |
| |
| /// A let else block does not diverge |
| LetElse, |
| |
| /// Method receiver |
| MethodReceiver, |
| |
| UnifyReceiver(Box<UnifyReceiverContext<'tcx>>), |
| |
| /// `return` with no expression |
| ReturnNoExpression, |
| |
| /// `return` with an expression |
| ReturnValue(HirId), |
| |
| /// Opaque return type of this function |
| OpaqueReturnType(Option<(Ty<'tcx>, Span)>), |
| |
| /// Block implicit return |
| BlockTailExpression(HirId, hir::MatchSource), |
| |
| /// #[feature(trivial_bounds)] is not enabled |
| TrivialBound, |
| |
| AwaitableExpr(HirId), |
| |
| ForLoopIterator, |
| |
| QuestionMark, |
| |
| /// Well-formed checking. If a `WellFormedLoc` is provided, |
| /// then it will be used to perform HIR-based wf checking |
| /// after an error occurs, in order to generate a more precise error span. |
| /// This is purely for diagnostic purposes - it is always |
| /// correct to use `MiscObligation` instead, or to specify |
| /// `WellFormed(None)` |
| WellFormed(Option<WellFormedLoc>), |
| |
| /// From `match_impl`. The cause for us having to match an impl, and the DefId we are matching against. |
| MatchImpl(ObligationCause<'tcx>, DefId), |
| |
| BinOp { |
| lhs_hir_id: HirId, |
| rhs_hir_id: Option<HirId>, |
| rhs_span: Option<Span>, |
| rhs_is_lit: bool, |
| output_ty: Option<Ty<'tcx>>, |
| }, |
| |
| AscribeUserTypeProvePredicate(Span), |
| |
| RustCall, |
| |
| /// Obligations to prove that a `std::ops::Drop` impl is not stronger than |
| /// the ADT it's being implemented for. |
| DropImpl, |
| |
| /// Requirement for a `const N: Ty` to implement `Ty: ConstParamTy` |
| ConstParam(Ty<'tcx>), |
| |
| /// Obligations emitted during the normalization of a weak type alias. |
| TypeAlias(InternedObligationCauseCode<'tcx>, Span, DefId), |
| } |
| |
| /// Whether a value can be extracted into a const. |
| /// Used for diagnostics around array repeat expressions. |
| #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| pub enum IsConstable { |
| No, |
| /// Call to a const fn |
| Fn, |
| /// Use of a const ctor |
| Ctor, |
| } |
| |
| crate::TrivialTypeTraversalAndLiftImpls! { |
| IsConstable, |
| } |
| |
| /// The 'location' at which we try to perform HIR-based wf checking. |
| /// This information is used to obtain an `hir::Ty`, which |
| /// we can walk in order to obtain precise spans for any |
| /// 'nested' types (e.g. `Foo` in `Option<Foo>`). |
| #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, Encodable, Decodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub enum WellFormedLoc { |
| /// Use the type of the provided definition. |
| Ty(LocalDefId), |
| /// Use the type of the parameter of the provided function. |
| /// We cannot use `hir::Param`, since the function may |
| /// not have a body (e.g. a trait method definition) |
| Param { |
| /// The function to lookup the parameter in |
| function: LocalDefId, |
| /// The index of the parameter to use. |
| /// Parameters are indexed from 0, with the return type |
| /// being the last 'parameter' |
| param_idx: usize, |
| }, |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub struct ImplDerivedObligationCause<'tcx> { |
| pub derived: DerivedObligationCause<'tcx>, |
| /// The `DefId` of the `impl` that gave rise to the `derived` obligation. |
| /// If the `derived` obligation arose from a trait alias, which conceptually has a synthetic impl, |
| /// then this will be the `DefId` of that trait alias. Care should therefore be taken to handle |
| /// that exceptional case where appropriate. |
| pub impl_or_alias_def_id: DefId, |
| /// The index of the derived predicate in the parent impl's predicates. |
| pub impl_def_predicate_index: Option<usize>, |
| pub span: Span, |
| } |
| |
| impl<'tcx> ObligationCauseCode<'tcx> { |
| /// Returns the base obligation, ignoring derived obligations. |
| pub fn peel_derives(&self) -> &Self { |
| let mut base_cause = self; |
| while let Some((parent_code, _)) = base_cause.parent() { |
| base_cause = parent_code; |
| } |
| base_cause |
| } |
| |
| /// Returns the base obligation and the base trait predicate, if any, ignoring |
| /// derived obligations. |
| pub fn peel_derives_with_predicate(&self) -> (&Self, Option<ty::PolyTraitPredicate<'tcx>>) { |
| let mut base_cause = self; |
| let mut base_trait_pred = None; |
| while let Some((parent_code, parent_pred)) = base_cause.parent() { |
| base_cause = parent_code; |
| if let Some(parent_pred) = parent_pred { |
| base_trait_pred = Some(parent_pred); |
| } |
| } |
| |
| (base_cause, base_trait_pred) |
| } |
| |
| pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> { |
| match self { |
| FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)), |
| BuiltinDerivedObligation(derived) |
| | WellFormedDerivedObligation(derived) |
| | ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => { |
| Some((&derived.parent_code, Some(derived.parent_trait_pred))) |
| } |
| _ => None, |
| } |
| } |
| |
| pub fn peel_match_impls(&self) -> &Self { |
| match self { |
| MatchImpl(cause, _) => cause.code(), |
| _ => self, |
| } |
| } |
| } |
| |
| // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger. |
| #[cfg(target_pointer_width = "64")] |
| rustc_data_structures::static_assert_size!(ObligationCauseCode<'_>, 48); |
| |
| #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] |
| pub enum StatementAsExpression { |
| CorrectType, |
| NeedsBoxing, |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub struct MatchExpressionArmCause<'tcx> { |
| pub arm_block_id: Option<HirId>, |
| pub arm_ty: Ty<'tcx>, |
| pub arm_span: Span, |
| pub prior_arm_block_id: Option<HirId>, |
| pub prior_arm_ty: Ty<'tcx>, |
| pub prior_arm_span: Span, |
| pub scrut_span: Span, |
| pub source: hir::MatchSource, |
| pub prior_non_diverging_arms: Vec<Span>, |
| // Is the expectation of this match expression an RPIT? |
| pub tail_defines_return_position_impl_trait: Option<LocalDefId>, |
| } |
| |
| #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
| #[derive(TypeFoldable, TypeVisitable, HashStable, TyEncodable, TyDecodable)] |
| pub struct IfExpressionCause<'tcx> { |
| pub then_id: HirId, |
| pub else_id: HirId, |
| pub then_ty: Ty<'tcx>, |
| pub else_ty: Ty<'tcx>, |
| pub outer_span: Option<Span>, |
| // Is the expectation of this match expression an RPIT? |
| pub tail_defines_return_position_impl_trait: Option<LocalDefId>, |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)] |
| #[derive(TypeVisitable, TypeFoldable)] |
| pub struct DerivedObligationCause<'tcx> { |
| /// The trait predicate of the parent obligation that led to the |
| /// current obligation. Note that only trait obligations lead to |
| /// derived obligations, so we just store the trait predicate here |
| /// directly. |
| pub parent_trait_pred: ty::PolyTraitPredicate<'tcx>, |
| |
| /// The parent trait had this cause. |
| pub parent_code: InternedObligationCauseCode<'tcx>, |
| } |
| |
| #[derive(Clone, Debug, TypeVisitable)] |
| pub enum SelectionError<'tcx> { |
| /// The trait is not implemented. |
| Unimplemented, |
| /// After a closure impl has selected, its "outputs" were evaluated |
| /// (which for closures includes the "input" type params) and they |
| /// didn't resolve. See `confirm_poly_trait_refs` for more. |
| SignatureMismatch(Box<SignatureMismatchData<'tcx>>), |
| /// The trait pointed by `DefId` is not object safe. |
| TraitNotObjectSafe(DefId), |
| /// A given constant couldn't be evaluated. |
| NotConstEvaluatable(NotConstEvaluatable), |
| /// Exceeded the recursion depth during type projection. |
| Overflow(OverflowError), |
| /// Computing an opaque type's hidden type caused an error (e.g. a cycle error). |
| /// We can thus not know whether the hidden type implements an auto trait, so |
| /// we should not presume anything about it. |
| OpaqueTypeAutoTraitLeakageUnknown(DefId), |
| } |
| |
| #[derive(Clone, Debug, TypeVisitable)] |
| pub struct SignatureMismatchData<'tcx> { |
| pub found_trait_ref: ty::TraitRef<'tcx>, |
| pub expected_trait_ref: ty::TraitRef<'tcx>, |
| pub terr: ty::error::TypeError<'tcx>, |
| } |
| |
| /// When performing resolution, it is typically the case that there |
| /// can be one of three outcomes: |
| /// |
| /// - `Ok(Some(r))`: success occurred with result `r` |
| /// - `Ok(None)`: could not definitely determine anything, usually due |
| /// to inconclusive type inference. |
| /// - `Err(e)`: error `e` occurred |
| pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>; |
| |
| /// Given the successful resolution of an obligation, the `ImplSource` |
| /// indicates where the impl comes from. |
| /// |
| /// For example, the obligation may be satisfied by a specific impl (case A), |
| /// or it may be relative to some bound that is in scope (case B). |
| /// |
| /// ```ignore (illustrative) |
| /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1 |
| /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2 |
| /// impl Clone for i32 { ... } // Impl_3 |
| /// |
| /// fn foo<T: Clone>(concrete: Option<Box<i32>>, param: T, mixed: Option<T>) { |
| /// // Case A: ImplSource points at a specific impl. Only possible when |
| /// // type is concretely known. If the impl itself has bounded |
| /// // type parameters, ImplSource will carry resolutions for those as well: |
| /// concrete.clone(); // ImplSource(Impl_1, [ImplSource(Impl_2, [ImplSource(Impl_3)])]) |
| /// |
| /// // Case B: ImplSource must be provided by caller. This applies when |
| /// // type is a type parameter. |
| /// param.clone(); // ImplSource::Param |
| /// |
| /// // Case C: A mix of cases A and B. |
| /// mixed.clone(); // ImplSource(Impl_1, [ImplSource::Param]) |
| /// } |
| /// ``` |
| /// |
| /// ### The type parameter `N` |
| /// |
| /// See explanation on `ImplSourceUserDefinedData`. |
| #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] |
| #[derive(TypeFoldable, TypeVisitable)] |
| pub enum ImplSource<'tcx, N> { |
| /// ImplSource identifying a particular impl. |
| UserDefined(ImplSourceUserDefinedData<'tcx, N>), |
| |
| /// Successful resolution to an obligation provided by the caller |
| /// for some type parameter. The `Vec<N>` represents the |
| /// obligations incurred from normalizing the where-clause (if |
| /// any). |
| Param(Vec<N>), |
| |
| /// Successful resolution for a builtin impl. |
| Builtin(BuiltinImplSource, Vec<N>), |
| } |
| |
| impl<'tcx, N> ImplSource<'tcx, N> { |
| pub fn nested_obligations(self) -> Vec<N> { |
| match self { |
| ImplSource::UserDefined(i) => i.nested, |
| ImplSource::Param(n) | ImplSource::Builtin(_, n) => n, |
| } |
| } |
| |
| pub fn borrow_nested_obligations(&self) -> &[N] { |
| match self { |
| ImplSource::UserDefined(i) => &i.nested, |
| ImplSource::Param(n) | ImplSource::Builtin(_, n) => n, |
| } |
| } |
| |
| pub fn borrow_nested_obligations_mut(&mut self) -> &mut [N] { |
| match self { |
| ImplSource::UserDefined(i) => &mut i.nested, |
| ImplSource::Param(n) | ImplSource::Builtin(_, n) => n, |
| } |
| } |
| |
| pub fn map<M, F>(self, f: F) -> ImplSource<'tcx, M> |
| where |
| F: FnMut(N) -> M, |
| { |
| match self { |
| ImplSource::UserDefined(i) => ImplSource::UserDefined(ImplSourceUserDefinedData { |
| impl_def_id: i.impl_def_id, |
| args: i.args, |
| nested: i.nested.into_iter().map(f).collect(), |
| }), |
| ImplSource::Param(n) => ImplSource::Param(n.into_iter().map(f).collect()), |
| ImplSource::Builtin(source, n) => { |
| ImplSource::Builtin(source, n.into_iter().map(f).collect()) |
| } |
| } |
| } |
| } |
| |
| /// Identifies a particular impl in the source, along with a set of |
| /// generic parameters from the impl's type/lifetime parameters. The |
| /// `nested` vector corresponds to the nested obligations attached to |
| /// the impl's type parameters. |
| /// |
| /// The type parameter `N` indicates the type used for "nested |
| /// obligations" that are required by the impl. During type-check, this |
| /// is `Obligation`, as one might expect. During codegen, however, this |
| /// is `()`, because codegen only requires a shallow resolution of an |
| /// impl, and nested obligations are satisfied later. |
| #[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] |
| #[derive(TypeFoldable, TypeVisitable)] |
| pub struct ImplSourceUserDefinedData<'tcx, N> { |
| pub impl_def_id: DefId, |
| pub args: GenericArgsRef<'tcx>, |
| pub nested: Vec<N>, |
| } |
| |
| #[derive(Copy, Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Debug)] |
| pub enum BuiltinImplSource { |
| /// Some builtin impl we don't need to differentiate. This should be used |
| /// unless more specific information is necessary. |
| Misc, |
| /// A builtin impl for trait objects. |
| /// |
| /// The vtable is formed by concatenating together the method lists of |
| /// the base object trait and all supertraits, pointers to supertrait vtable will |
| /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods |
| /// in that vtable. |
| Object { vtable_base: usize }, |
| /// The vtable is formed by concatenating together the method lists of |
| /// the base object trait and all supertraits, pointers to supertrait vtable will |
| /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable |
| /// within that vtable. |
| TraitUpcasting { vtable_vptr_slot: Option<usize> }, |
| /// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`. |
| /// |
| /// This needs to be a separate variant as it is still unstable and we need to emit |
| /// a feature error when using it on stable. |
| TupleUnsizing, |
| } |
| |
| TrivialTypeTraversalImpls! { BuiltinImplSource } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)] |
| pub enum ObjectSafetyViolation { |
| /// `Self: Sized` declared on the trait. |
| SizedSelf(SmallVec<[Span; 1]>), |
| |
| /// Supertrait reference references `Self` an in illegal location |
| /// (e.g., `trait Foo : Bar<Self>`). |
| SupertraitSelf(SmallVec<[Span; 1]>), |
| |
| // Supertrait has a non-lifetime `for<T>` binder. |
| SupertraitNonLifetimeBinder(SmallVec<[Span; 1]>), |
| |
| /// Method has something illegal. |
| Method(Symbol, MethodViolationCode, Span), |
| |
| /// Associated const. |
| AssocConst(Symbol, Span), |
| |
| /// GAT |
| GAT(Symbol, Span), |
| } |
| |
| impl ObjectSafetyViolation { |
| pub fn error_msg(&self) -> Cow<'static, str> { |
| match self { |
| ObjectSafetyViolation::SizedSelf(_) => "it requires `Self: Sized`".into(), |
| ObjectSafetyViolation::SupertraitSelf(ref spans) => { |
| if spans.iter().any(|sp| *sp != DUMMY_SP) { |
| "it uses `Self` as a type parameter".into() |
| } else { |
| "it cannot use `Self` as a type parameter in a supertrait or `where`-clause" |
| .into() |
| } |
| } |
| ObjectSafetyViolation::SupertraitNonLifetimeBinder(_) => { |
| "where clause cannot reference non-lifetime `for<...>` variables".into() |
| } |
| ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => { |
| format!("associated function `{name}` has no `self` parameter").into() |
| } |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::ReferencesSelfInput(_), |
| DUMMY_SP, |
| ) => format!("method `{name}` references the `Self` type in its parameters").into(), |
| ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => { |
| format!("method `{name}` references the `Self` type in this parameter").into() |
| } |
| ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => { |
| format!("method `{name}` references the `Self` type in its return type").into() |
| } |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::ReferencesImplTraitInTrait(_), |
| _, |
| ) => { |
| format!("method `{name}` references an `impl Trait` type in its return type").into() |
| } |
| ObjectSafetyViolation::Method(name, MethodViolationCode::AsyncFn, _) => { |
| format!("method `{name}` is `async`").into() |
| } |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::WhereClauseReferencesSelf, |
| _, |
| ) => format!("method `{name}` references the `Self` type in its `where` clause").into(), |
| ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => { |
| format!("method `{name}` has generic type parameters").into() |
| } |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::UndispatchableReceiver(_), |
| _, |
| ) => format!("method `{name}`'s `self` parameter cannot be dispatched on").into(), |
| ObjectSafetyViolation::AssocConst(name, DUMMY_SP) => { |
| format!("it contains associated `const` `{name}`").into() |
| } |
| ObjectSafetyViolation::AssocConst(..) => "it contains this associated `const`".into(), |
| ObjectSafetyViolation::GAT(name, _) => { |
| format!("it contains the generic associated type `{name}`").into() |
| } |
| } |
| } |
| |
| pub fn solution(&self) -> ObjectSafetyViolationSolution { |
| match self { |
| ObjectSafetyViolation::SizedSelf(_) |
| | ObjectSafetyViolation::SupertraitSelf(_) |
| | ObjectSafetyViolation::SupertraitNonLifetimeBinder(..) => { |
| ObjectSafetyViolationSolution::None |
| } |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))), |
| _, |
| ) => ObjectSafetyViolationSolution::AddSelfOrMakeSized { |
| name: *name, |
| add_self_sugg: add_self_sugg.clone(), |
| make_sized_sugg: make_sized_sugg.clone(), |
| }, |
| ObjectSafetyViolation::Method( |
| name, |
| MethodViolationCode::UndispatchableReceiver(Some(span)), |
| _, |
| ) => ObjectSafetyViolationSolution::ChangeToRefSelf(*name, *span), |
| ObjectSafetyViolation::AssocConst(name, _) |
| | ObjectSafetyViolation::GAT(name, _) |
| | ObjectSafetyViolation::Method(name, ..) => { |
| ObjectSafetyViolationSolution::MoveToAnotherTrait(*name) |
| } |
| } |
| } |
| |
| pub fn spans(&self) -> SmallVec<[Span; 1]> { |
| // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so |
| // diagnostics use a `note` instead of a `span_label`. |
| match self { |
| ObjectSafetyViolation::SupertraitSelf(spans) |
| | ObjectSafetyViolation::SizedSelf(spans) |
| | ObjectSafetyViolation::SupertraitNonLifetimeBinder(spans) => spans.clone(), |
| ObjectSafetyViolation::AssocConst(_, span) |
| | ObjectSafetyViolation::GAT(_, span) |
| | ObjectSafetyViolation::Method(_, _, span) |
| if *span != DUMMY_SP => |
| { |
| smallvec![*span] |
| } |
| _ => smallvec![], |
| } |
| } |
| } |
| |
| #[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)] |
| pub enum ObjectSafetyViolationSolution { |
| None, |
| AddSelfOrMakeSized { |
| name: Symbol, |
| add_self_sugg: (String, Span), |
| make_sized_sugg: (String, Span), |
| }, |
| ChangeToRefSelf(Symbol, Span), |
| MoveToAnotherTrait(Symbol), |
| } |
| |
| impl ObjectSafetyViolationSolution { |
| pub fn add_to<G: EmissionGuarantee>(self, err: &mut Diag<'_, G>) { |
| match self { |
| ObjectSafetyViolationSolution::None => {} |
| ObjectSafetyViolationSolution::AddSelfOrMakeSized { |
| name, |
| add_self_sugg, |
| make_sized_sugg, |
| } => { |
| err.span_suggestion( |
| add_self_sugg.1, |
| format!( |
| "consider turning `{name}` into a method by giving it a `&self` argument" |
| ), |
| add_self_sugg.0, |
| Applicability::MaybeIncorrect, |
| ); |
| err.span_suggestion( |
| make_sized_sugg.1, |
| format!( |
| "alternatively, consider constraining `{name}` so it does not apply to \ |
| trait objects" |
| ), |
| make_sized_sugg.0, |
| Applicability::MaybeIncorrect, |
| ); |
| } |
| ObjectSafetyViolationSolution::ChangeToRefSelf(name, span) => { |
| err.span_suggestion( |
| span, |
| format!("consider changing method `{name}`'s `self` parameter to be `&self`"), |
| "&Self", |
| Applicability::MachineApplicable, |
| ); |
| } |
| ObjectSafetyViolationSolution::MoveToAnotherTrait(name) => { |
| err.help(format!("consider moving `{name}` to another trait")); |
| } |
| } |
| } |
| } |
| |
| /// Reasons a method might not be object-safe. |
| #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)] |
| pub enum MethodViolationCode { |
| /// e.g., `fn foo()` |
| StaticMethod(Option<(/* add &self */ (String, Span), /* add Self: Sized */ (String, Span))>), |
| |
| /// e.g., `fn foo(&self, x: Self)` |
| ReferencesSelfInput(Option<Span>), |
| |
| /// e.g., `fn foo(&self) -> Self` |
| ReferencesSelfOutput, |
| |
| /// e.g., `fn foo(&self) -> impl Sized` |
| ReferencesImplTraitInTrait(Span), |
| |
| /// e.g., `async fn foo(&self)` |
| AsyncFn, |
| |
| /// e.g., `fn foo(&self) where Self: Clone` |
| WhereClauseReferencesSelf, |
| |
| /// e.g., `fn foo<A>()` |
| Generic, |
| |
| /// the method's receiver (`self` argument) can't be dispatched on |
| UndispatchableReceiver(Option<Span>), |
| } |
| |
| /// These are the error cases for `codegen_select_candidate`. |
| #[derive(Copy, Clone, Debug, Hash, HashStable, Encodable, Decodable)] |
| pub enum CodegenObligationError { |
| /// Ambiguity can happen when monomorphizing during trans |
| /// expands to some humongous type that never occurred |
| /// statically -- this humongous type can then overflow, |
| /// leading to an ambiguous result. So report this as an |
| /// overflow bug, since I believe this is the only case |
| /// where ambiguity can result. |
| Ambiguity, |
| /// This can trigger when we probe for the source of a `'static` lifetime requirement |
| /// on a trait object: `impl Foo for dyn Trait {}` has an implicit `'static` bound. |
| /// This can also trigger when we have a global bound that is not actually satisfied, |
| /// but was included during typeck due to the trivial_bounds feature. |
| Unimplemented, |
| FulfillmentError, |
| } |
