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Diffstat (limited to 'compiler/rustc_middle/src/traits/mod.rs')
| -rw-r--r-- | compiler/rustc_middle/src/traits/mod.rs | 1026 |
1 files changed, 1026 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs new file mode 100644 index 000000000..72b848c3e --- /dev/null +++ b/compiler/rustc_middle/src/traits/mod.rs @@ -0,0 +1,1026 @@ +//! 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 + +mod chalk; +pub mod query; +pub mod select; +pub mod specialization_graph; +mod structural_impls; +pub mod util; + +use crate::infer::canonical::Canonical; +use crate::ty::abstract_const::NotConstEvaluatable; +use crate::ty::subst::SubstsRef; +use crate::ty::{self, AdtKind, Predicate, Ty, TyCtxt}; + +use rustc_data_structures::sync::Lrc; +use rustc_errors::{Applicability, Diagnostic}; +use rustc_hir as hir; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_span::symbol::Symbol; +use rustc_span::{Span, DUMMY_SP}; +use smallvec::SmallVec; + +use std::borrow::Cow; +use std::hash::{Hash, Hasher}; + +pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache}; + +pub type CanonicalChalkEnvironmentAndGoal<'tcx> = Canonical<'tcx, ChalkEnvironmentAndGoal<'tcx>>; + +pub use self::ObligationCauseCode::*; + +pub use self::chalk::{ChalkEnvironmentAndGoal, RustInterner as ChalkRustInterner}; + +/// Depending on the stage of compilation, we want projection to be +/// more or less conservative. +#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)] +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, Lift)] +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: hir::HirId, + + 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: hir::HirId, + code: ObligationCauseCode<'tcx>, + ) -> ObligationCause<'tcx> { + ObligationCause { span, body_id, code: code.into() } + } + + pub fn misc(span: Span, body_id: hir::HirId) -> 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: hir::CRATE_HIR_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 or just a CLI argument. + self.code = + variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into(); + self + } +} + +#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] +pub struct UnifyReceiverContext<'tcx> { + pub assoc_item: ty::AssocItem, + pub param_env: ty::ParamEnv<'tcx>, + pub substs: SubstsRef<'tcx>, +} + +#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift, Default)] +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> 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, Hash, Lift)] +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, + + /// This is the trait reference from the given projection. + ProjectionWf(ty::ProjectionTy<'tcx>), + + /// In an impl of trait `X` for type `Y`, type `Y` must + /// also implement all supertraits of `X`. + ItemObligation(DefId), + + /// Like `ItemObligation`, but with extra detail on the source of the obligation. + BindingObligation(DefId, Span), + + /// 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 an object cast. + ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'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(hir::HirId), + /// Argument type must be `Sized`. + SizedArgumentType(Option<Span>), + /// Return type must be `Sized`. + SizedReturnType, + /// Yield type must be `Sized`. + SizedYieldType, + /// Box expression result type must be `Sized`. + SizedBoxType, + /// Inline asm operand type must be `Sized`. + InlineAsmSized, + /// `[expr; N]` requires `type_of(expr): Copy`. + RepeatElementCopy { + /// If element is a `const fn` we display a help message suggesting to move the + /// function call to a new `const` item while saying that `T` doesn't implement `Copy`. + is_const_fn: bool, + }, + + /// 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, + + BuiltinDerivedObligation(DerivedObligationCause<'tcx>), + + ImplDerivedObligation(Box<ImplDerivedObligationCause<'tcx>>), + + DerivedObligation(DerivedObligationCause<'tcx>), + + FunctionArgumentObligation { + /// The node of the relevant argument in the function call. + arg_hir_id: hir::HirId, + /// The node of the function call. + call_hir_id: hir::HirId, + /// The obligation introduced by this argument. + parent_code: InternedObligationCauseCode<'tcx>, + }, + + /// Error derived when matching traits/impls; see ObligationCause for more details + 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, + }, + + /// Constants in patterns must have `Structural` type. + ConstPatternStructural, + + /// 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, + + /// 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(hir::HirId), + + /// Return type of this function + ReturnType, + + /// Opaque return type of this function + OpaqueReturnType(Option<(Ty<'tcx>, Span)>), + + /// Block implicit return + BlockTailExpression(hir::HirId), + + /// #[feature(trivial_bounds)] is not enabled + TrivialBound, + + /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y` + OpaqueType, + + AwaitableExpr(Option<hir::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 { + rhs_span: Option<Span>, + is_lit: bool, + output_pred: Option<Predicate<'tcx>>, + }, +} + +/// 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)] +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: u16, + }, +} + +#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] +pub struct ImplDerivedObligationCause<'tcx> { + pub derived: DerivedObligationCause<'tcx>, + pub impl_def_id: DefId, + pub span: Span, +} + +impl<'tcx> ObligationCauseCode<'tcx> { + // Return 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 + } + + pub fn parent(&self) -> Option<(&Self, Option<ty::PolyTraitPredicate<'tcx>>)> { + match self { + FunctionArgumentObligation { parent_code, .. } => Some((parent_code, None)), + BuiltinDerivedObligation(derived) + | DerivedObligation(derived) + | ImplDerivedObligation(box ImplDerivedObligationCause { derived, .. }) => { + Some((&derived.parent_code, Some(derived.parent_trait_pred))) + } + _ => None, + } + } +} + +// `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger. +#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] +static_assert_size!(ObligationCauseCode<'_>, 48); + +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +pub enum StatementAsExpression { + CorrectType, + NeedsBoxing, +} + +impl<'tcx> ty::Lift<'tcx> for StatementAsExpression { + type Lifted = StatementAsExpression; + fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<StatementAsExpression> { + Some(self) + } +} + +#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] +pub struct MatchExpressionArmCause<'tcx> { + pub arm_block_id: Option<hir::HirId>, + pub arm_ty: Ty<'tcx>, + pub arm_span: Span, + pub prior_arm_block_id: Option<hir::HirId>, + pub prior_arm_ty: Ty<'tcx>, + pub prior_arm_span: Span, + pub scrut_span: Span, + pub source: hir::MatchSource, + pub prior_arms: Vec<Span>, + pub scrut_hir_id: hir::HirId, + pub opt_suggest_box_span: Option<Span>, +} + +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +#[derive(Lift, TypeFoldable, TypeVisitable)] +pub struct IfExpressionCause<'tcx> { + pub then_id: hir::HirId, + pub else_id: hir::HirId, + pub then_ty: Ty<'tcx>, + pub else_ty: Ty<'tcx>, + pub outer_span: Option<Span>, + pub opt_suggest_box_span: Option<Span>, +} + +#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)] +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, TypeFoldable, TypeVisitable, Lift)] +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. + OutputTypeParameterMismatch( + ty::PolyTraitRef<'tcx>, + ty::PolyTraitRef<'tcx>, + ty::error::TypeError<'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), + /// Signaling that an error has already been emitted, to avoid + /// multiple errors being shown. + ErrorReporting, + /// Multiple applicable `impl`s where found. The `DefId`s correspond to + /// all the `impl`s' Items. + Ambiguous(Vec<DefId>), +} + +/// 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 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, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub enum ImplSource<'tcx, N> { + /// ImplSource identifying a particular impl. + UserDefined(ImplSourceUserDefinedData<'tcx, N>), + + /// ImplSource for auto trait implementations. + /// This carries the information and nested obligations with regards + /// to an auto implementation for a trait `Trait`. The nested obligations + /// ensure the trait implementation holds for all the constituent types. + AutoImpl(ImplSourceAutoImplData<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>, ty::BoundConstness), + + /// Virtual calls through an object. + Object(ImplSourceObjectData<'tcx, N>), + + /// Successful resolution for a builtin trait. + Builtin(ImplSourceBuiltinData<N>), + + /// ImplSource for trait upcasting coercion + TraitUpcasting(ImplSourceTraitUpcastingData<'tcx, N>), + + /// ImplSource automatically generated for a closure. The `DefId` is the ID + /// of the closure expression. This is an `ImplSource::UserDefined` in spirit, but the + /// impl is generated by the compiler and does not appear in the source. + Closure(ImplSourceClosureData<'tcx, N>), + + /// Same as above, but for a function pointer type with the given signature. + FnPointer(ImplSourceFnPointerData<'tcx, N>), + + /// ImplSource for a builtin `DeterminantKind` trait implementation. + DiscriminantKind(ImplSourceDiscriminantKindData), + + /// ImplSource for a builtin `Pointee` trait implementation. + Pointee(ImplSourcePointeeData), + + /// ImplSource automatically generated for a generator. + Generator(ImplSourceGeneratorData<'tcx, N>), + + /// ImplSource for a trait alias. + TraitAlias(ImplSourceTraitAliasData<'tcx, N>), + + /// ImplSource for a `const Drop` implementation. + ConstDestruct(ImplSourceConstDestructData<N>), +} + +impl<'tcx, N> ImplSource<'tcx, N> { + pub fn nested_obligations(self) -> Vec<N> { + match self { + ImplSource::UserDefined(i) => i.nested, + ImplSource::Param(n, _) => n, + ImplSource::Builtin(i) => i.nested, + ImplSource::AutoImpl(d) => d.nested, + ImplSource::Closure(c) => c.nested, + ImplSource::Generator(c) => c.nested, + ImplSource::Object(d) => d.nested, + ImplSource::FnPointer(d) => d.nested, + ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) + | ImplSource::Pointee(ImplSourcePointeeData) => Vec::new(), + ImplSource::TraitAlias(d) => d.nested, + ImplSource::TraitUpcasting(d) => d.nested, + ImplSource::ConstDestruct(i) => i.nested, + } + } + + pub fn borrow_nested_obligations(&self) -> &[N] { + match &self { + ImplSource::UserDefined(i) => &i.nested[..], + ImplSource::Param(n, _) => &n, + ImplSource::Builtin(i) => &i.nested, + ImplSource::AutoImpl(d) => &d.nested, + ImplSource::Closure(c) => &c.nested, + ImplSource::Generator(c) => &c.nested, + ImplSource::Object(d) => &d.nested, + ImplSource::FnPointer(d) => &d.nested, + ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) + | ImplSource::Pointee(ImplSourcePointeeData) => &[], + ImplSource::TraitAlias(d) => &d.nested, + ImplSource::TraitUpcasting(d) => &d.nested, + ImplSource::ConstDestruct(i) => &i.nested, + } + } + + 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, + substs: i.substs, + nested: i.nested.into_iter().map(f).collect(), + }), + ImplSource::Param(n, ct) => ImplSource::Param(n.into_iter().map(f).collect(), ct), + ImplSource::Builtin(i) => ImplSource::Builtin(ImplSourceBuiltinData { + nested: i.nested.into_iter().map(f).collect(), + }), + ImplSource::Object(o) => ImplSource::Object(ImplSourceObjectData { + upcast_trait_ref: o.upcast_trait_ref, + vtable_base: o.vtable_base, + nested: o.nested.into_iter().map(f).collect(), + }), + ImplSource::AutoImpl(d) => ImplSource::AutoImpl(ImplSourceAutoImplData { + trait_def_id: d.trait_def_id, + nested: d.nested.into_iter().map(f).collect(), + }), + ImplSource::Closure(c) => ImplSource::Closure(ImplSourceClosureData { + closure_def_id: c.closure_def_id, + substs: c.substs, + nested: c.nested.into_iter().map(f).collect(), + }), + ImplSource::Generator(c) => ImplSource::Generator(ImplSourceGeneratorData { + generator_def_id: c.generator_def_id, + substs: c.substs, + nested: c.nested.into_iter().map(f).collect(), + }), + ImplSource::FnPointer(p) => ImplSource::FnPointer(ImplSourceFnPointerData { + fn_ty: p.fn_ty, + nested: p.nested.into_iter().map(f).collect(), + }), + ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) => { + ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) + } + ImplSource::Pointee(ImplSourcePointeeData) => { + ImplSource::Pointee(ImplSourcePointeeData) + } + ImplSource::TraitAlias(d) => ImplSource::TraitAlias(ImplSourceTraitAliasData { + alias_def_id: d.alias_def_id, + substs: d.substs, + nested: d.nested.into_iter().map(f).collect(), + }), + ImplSource::TraitUpcasting(d) => { + ImplSource::TraitUpcasting(ImplSourceTraitUpcastingData { + upcast_trait_ref: d.upcast_trait_ref, + vtable_vptr_slot: d.vtable_vptr_slot, + nested: d.nested.into_iter().map(f).collect(), + }) + } + ImplSource::ConstDestruct(i) => { + ImplSource::ConstDestruct(ImplSourceConstDestructData { + nested: i.nested.into_iter().map(f).collect(), + }) + } + } + } +} + +/// Identifies a particular impl in the source, along with a set of +/// substitutions 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, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceUserDefinedData<'tcx, N> { + pub impl_def_id: DefId, + pub substs: SubstsRef<'tcx>, + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceGeneratorData<'tcx, N> { + pub generator_def_id: DefId, + pub substs: SubstsRef<'tcx>, + /// Nested obligations. This can be non-empty if the generator + /// signature contains associated types. + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceClosureData<'tcx, N> { + pub closure_def_id: DefId, + pub substs: SubstsRef<'tcx>, + /// Nested obligations. This can be non-empty if the closure + /// signature contains associated types. + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceAutoImplData<N> { + pub trait_def_id: DefId, + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceTraitUpcastingData<'tcx, N> { + /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`. + pub upcast_trait_ref: ty::PolyTraitRef<'tcx>, + + /// 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. + pub vtable_vptr_slot: Option<usize>, + + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceBuiltinData<N> { + pub nested: Vec<N>, +} + +#[derive(PartialEq, Eq, Clone, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceObjectData<'tcx, N> { + /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`. + pub upcast_trait_ref: ty::PolyTraitRef<'tcx>, + + /// 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. + pub vtable_base: usize, + + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceFnPointerData<'tcx, N> { + pub fn_ty: Ty<'tcx>, + pub nested: Vec<N>, +} + +// FIXME(@lcnr): This should be refactored and merged with other builtin vtables. +#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] +pub struct ImplSourceDiscriminantKindData; + +#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, HashStable)] +pub struct ImplSourcePointeeData; + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceConstDestructData<N> { + pub nested: Vec<N>, +} + +#[derive(Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Lift)] +#[derive(TypeFoldable, TypeVisitable)] +pub struct ImplSourceTraitAliasData<'tcx, N> { + pub alias_def_id: DefId, + pub substs: SubstsRef<'tcx>, + pub nested: Vec<N>, +} + +#[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]>), + + /// 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::Method(name, MethodViolationCode::StaticMethod(_), _) => { + format!("associated function `{}` has no `self` parameter", name).into() + } + ObjectSafetyViolation::Method( + name, + MethodViolationCode::ReferencesSelfInput(_), + DUMMY_SP, + ) => format!("method `{}` references the `Self` type in its parameters", name).into(), + ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfInput(_), _) => { + format!("method `{}` references the `Self` type in this parameter", name).into() + } + ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelfOutput, _) => { + format!("method `{}` references the `Self` type in its return type", name).into() + } + ObjectSafetyViolation::Method( + name, + MethodViolationCode::WhereClauseReferencesSelf, + _, + ) => { + format!("method `{}` references the `Self` type in its `where` clause", name).into() + } + ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => { + format!("method `{}` has generic type parameters", name).into() + } + ObjectSafetyViolation::Method( + name, + MethodViolationCode::UndispatchableReceiver(_), + _, + ) => format!("method `{}`'s `self` parameter cannot be dispatched on", name).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, err: &mut Diagnostic) { + match self { + ObjectSafetyViolation::SizedSelf(_) | ObjectSafetyViolation::SupertraitSelf(_) => {} + ObjectSafetyViolation::Method( + name, + MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))), + _, + ) => { + err.span_suggestion( + add_self_sugg.1, + format!( + "consider turning `{}` into a method by giving it a `&self` argument", + name + ), + add_self_sugg.0.to_string(), + Applicability::MaybeIncorrect, + ); + err.span_suggestion( + make_sized_sugg.1, + format!( + "alternatively, consider constraining `{}` so it does not apply to \ + trait objects", + name + ), + make_sized_sugg.0.to_string(), + Applicability::MaybeIncorrect, + ); + } + ObjectSafetyViolation::Method( + name, + MethodViolationCode::UndispatchableReceiver(Some(span)), + _, + ) => { + err.span_suggestion( + *span, + &format!( + "consider changing method `{}`'s `self` parameter to be `&self`", + name + ), + "&Self", + Applicability::MachineApplicable, + ); + } + ObjectSafetyViolation::AssocConst(name, _) + | ObjectSafetyViolation::GAT(name, _) + | ObjectSafetyViolation::Method(name, ..) => { + err.help(&format!("consider moving `{}` to another trait", 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) => spans.clone(), + ObjectSafetyViolation::AssocConst(_, span) + | ObjectSafetyViolation::GAT(_, span) + | ObjectSafetyViolation::Method(_, _, span) + if *span != DUMMY_SP => + { + smallvec![*span] + } + _ => smallvec![], + } + } +} + +/// 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) 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_fulfill_obligation`. +#[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, +} |