rustc_middle/traits/mod.rs
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//! 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;
use std::borrow::Cow;
use std::hash::{Hash, Hasher};
use rustc_data_structures::sync::Lrc;
use rustc_errors::{Applicability, Diag, EmissionGuarantee};
use rustc_hir as hir;
use rustc_hir::HirId;
use rustc_hir::def_id::DefId;
use rustc_macros::{
Decodable, Encodable, HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable,
};
use rustc_span::def_id::{CRATE_DEF_ID, LocalDefId};
use rustc_span::symbol::Symbol;
use rustc_span::{DUMMY_SP, Span};
// FIXME: Remove this import and import via `solve::`
pub use rustc_type_ir::solve::BuiltinImplSource;
use smallvec::{SmallVec, smallvec};
use thin_vec::ThinVec;
pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
use crate::mir::ConstraintCategory;
use crate::ty::abstract_const::NotConstEvaluatable;
use crate::ty::{self, AdtKind, GenericArgsRef, Ty};
/// 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, ObligationCauseCode::Misc)
}
#[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() }
}
#[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(DerivedCause<'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(DerivedCause { parent_trait_pred, parent_code: self.code }).into();
self
}
pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
match self.code() {
ObligationCauseCode::MatchImpl(cause, _) => cause.to_constraint_category(),
ObligationCauseCode::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::Misc` (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::Misc = 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::Misc)
}
}
#[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.
Misc,
/// A slice or array is WF only if `T: Sized`.
SliceOrArrayElem,
/// A tuple is WF only if its middle elements are `Sized`.
TupleElem,
/// Represents a clause that comes from a specific item.
/// The span corresponds to the clause.
WhereClause(DefId, Span),
/// Represents a bound for an opaque we are checking the well-formedness of.
/// The def-id corresponds to a specific definition site that we found the
/// hidden type from, if any.
OpaqueTypeBound(Span, Option<LocalDefId>),
/// Like `WhereClause`, but also identifies the expression
/// which requires the `where` clause to be proven, and also
/// identifies the index of the predicate in the `predicates_of`
/// list of the item.
WhereClauseInExpr(DefId, Span, HirId, usize),
/// Like `WhereClauseinExpr`, but indexes into the `const_conditions`
/// rather than the `predicates_of`.
HostEffectInExpr(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`.
BuiltinDerived(DerivedCause<'tcx>),
/// Derived obligation (i.e. `where` clause) on an user-provided impl
/// or a trait alias.
ImplDerived(Box<ImplDerivedCause<'tcx>>),
/// Derived obligation for WF goals.
WellFormedDerived(DerivedCause<'tcx>),
/// Derived obligation refined to point at a specific argument in
/// a call or method expression.
FunctionArg {
/// 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
CompareImplItem {
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>, HirId)>),
/// 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 `Misc` 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 ImplDerivedCause<'tcx> {
pub derived: DerivedCause<'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 {
ObligationCauseCode::FunctionArg { parent_code, .. } => Some((parent_code, None)),
ObligationCauseCode::BuiltinDerived(derived)
| ObligationCauseCode::WellFormedDerived(derived)
| ObligationCauseCode::ImplDerived(box ImplDerivedCause { derived, .. }) => {
Some((&derived.parent_code, Some(derived.parent_trait_pred)))
}
_ => None,
}
}
pub fn peel_match_impls(&self) -> &Self {
match self {
ObligationCauseCode::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,
/// Span of the scrutinee of the match (the matched value).
pub scrut_span: Span,
/// Source of the match, i.e. `match` or a desugaring.
pub source: hir::MatchSource,
/// Span of the *whole* match expr.
pub expr_span: Span,
/// Spans of the previous arms except for those that diverge (i.e. evaluate to `!`).
///
/// These are used for pointing out errors that may affect several arms.
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 DerivedCause<'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, PartialEq, Eq, 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 dyn-incompatible.
TraitDynIncompatible(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),
/// Error for a `ConstArgHasType` goal
ConstArgHasWrongType { ct: ty::Const<'tcx>, ct_ty: Ty<'tcx>, expected_ty: Ty<'tcx> },
}
#[derive(Clone, Debug, PartialEq, Eq, 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(ThinVec<N>),
/// Successful resolution for a builtin impl.
Builtin(BuiltinImplSource, ThinVec<N>),
}
impl<'tcx, N> ImplSource<'tcx, N> {
pub fn nested_obligations(self) -> ThinVec<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: ThinVec<N>,
}
#[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
pub enum DynCompatibilityViolation {
/// `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 DynCompatibilityViolation {
pub fn error_msg(&self) -> Cow<'static, str> {
match self {
DynCompatibilityViolation::SizedSelf(_) => "it requires `Self: Sized`".into(),
DynCompatibilityViolation::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()
}
}
DynCompatibilityViolation::SupertraitNonLifetimeBinder(_) => {
"where clause cannot reference non-lifetime `for<...>` variables".into()
}
DynCompatibilityViolation::Method(name, MethodViolationCode::StaticMethod(_), _) => {
format!("associated function `{name}` has no `self` parameter").into()
}
DynCompatibilityViolation::Method(
name,
MethodViolationCode::ReferencesSelfInput(_),
DUMMY_SP,
) => format!("method `{name}` references the `Self` type in its parameters").into(),
DynCompatibilityViolation::Method(
name,
MethodViolationCode::ReferencesSelfInput(_),
_,
) => format!("method `{name}` references the `Self` type in this parameter").into(),
DynCompatibilityViolation::Method(
name,
MethodViolationCode::ReferencesSelfOutput,
_,
) => format!("method `{name}` references the `Self` type in its return type").into(),
DynCompatibilityViolation::Method(
name,
MethodViolationCode::ReferencesImplTraitInTrait(_),
_,
) => {
format!("method `{name}` references an `impl Trait` type in its return type").into()
}
DynCompatibilityViolation::Method(name, MethodViolationCode::AsyncFn, _) => {
format!("method `{name}` is `async`").into()
}
DynCompatibilityViolation::Method(
name,
MethodViolationCode::WhereClauseReferencesSelf,
_,
) => format!("method `{name}` references the `Self` type in its `where` clause").into(),
DynCompatibilityViolation::Method(name, MethodViolationCode::Generic, _) => {
format!("method `{name}` has generic type parameters").into()
}
DynCompatibilityViolation::Method(
name,
MethodViolationCode::UndispatchableReceiver(_),
_,
) => format!("method `{name}`'s `self` parameter cannot be dispatched on").into(),
DynCompatibilityViolation::AssocConst(name, DUMMY_SP) => {
format!("it contains associated `const` `{name}`").into()
}
DynCompatibilityViolation::AssocConst(..) => {
"it contains this associated `const`".into()
}
DynCompatibilityViolation::GAT(name, _) => {
format!("it contains the generic associated type `{name}`").into()
}
}
}
pub fn solution(&self) -> DynCompatibilityViolationSolution {
match self {
DynCompatibilityViolation::SizedSelf(_)
| DynCompatibilityViolation::SupertraitSelf(_)
| DynCompatibilityViolation::SupertraitNonLifetimeBinder(..) => {
DynCompatibilityViolationSolution::None
}
DynCompatibilityViolation::Method(
name,
MethodViolationCode::StaticMethod(Some((add_self_sugg, make_sized_sugg))),
_,
) => DynCompatibilityViolationSolution::AddSelfOrMakeSized {
name: *name,
add_self_sugg: add_self_sugg.clone(),
make_sized_sugg: make_sized_sugg.clone(),
},
DynCompatibilityViolation::Method(
name,
MethodViolationCode::UndispatchableReceiver(Some(span)),
_,
) => DynCompatibilityViolationSolution::ChangeToRefSelf(*name, *span),
DynCompatibilityViolation::AssocConst(name, _)
| DynCompatibilityViolation::GAT(name, _)
| DynCompatibilityViolation::Method(name, ..) => {
DynCompatibilityViolationSolution::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 {
DynCompatibilityViolation::SupertraitSelf(spans)
| DynCompatibilityViolation::SizedSelf(spans)
| DynCompatibilityViolation::SupertraitNonLifetimeBinder(spans) => spans.clone(),
DynCompatibilityViolation::AssocConst(_, span)
| DynCompatibilityViolation::GAT(_, span)
| DynCompatibilityViolation::Method(_, _, span)
if *span != DUMMY_SP =>
{
smallvec![*span]
}
_ => smallvec![],
}
}
}
#[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub enum DynCompatibilityViolationSolution {
None,
AddSelfOrMakeSized {
name: Symbol,
add_self_sugg: (String, Span),
make_sized_sugg: (String, Span),
},
ChangeToRefSelf(Symbol, Span),
MoveToAnotherTrait(Symbol),
}
impl DynCompatibilityViolationSolution {
pub fn add_to<G: EmissionGuarantee>(self, err: &mut Diag<'_, G>) {
match self {
DynCompatibilityViolationSolution::None => {}
DynCompatibilityViolationSolution::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,
);
}
DynCompatibilityViolationSolution::ChangeToRefSelf(name, span) => {
err.span_suggestion(
span,
format!("consider changing method `{name}`'s `self` parameter to be `&self`"),
"&Self",
Applicability::MachineApplicable,
);
}
DynCompatibilityViolationSolution::MoveToAnotherTrait(name) => {
err.help(format!("consider moving `{name}` to another trait"));
}
}
}
}
/// Reasons a method might not be dyn-compatible.
#[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,
}