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Move traits::select datatypes to traits::types.

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This commit is contained in:
Camille GILLOT 2020-01-22 09:01:22 +01:00
parent a2cd0715fd
commit a77da35ed4
4 changed files with 290 additions and 295 deletions
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3
src/librustc/traits/mod.rs
View File

@ -52,8 +52,7 @@ pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
pub use self::project::MismatchedProjectionTypes; pub use self::project::MismatchedProjectionTypes;
pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type}; pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
pub use self::project::{Normalized, ProjectionCache, ProjectionCacheSnapshot}; pub use self::project::{Normalized, ProjectionCache, ProjectionCacheSnapshot};
pub use self::select::{EvaluationCache, SelectionCache, SelectionContext}; pub use self::select::{IntercrateAmbiguityCause, SelectionContext};
pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
pub use self::specialize::find_associated_item; pub use self::specialize::find_associated_item;
pub use self::specialize::specialization_graph::FutureCompatOverlapError; pub use self::specialize::specialization_graph::FutureCompatOverlapError;
pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind; pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;

295
src/librustc/traits/select.rs
View File

@ -41,7 +41,6 @@ use crate::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, Wit
use rustc_hir::def_id::DefId; use rustc_hir::def_id::DefId;
use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::sync::Lock;
use rustc_hir as hir; use rustc_hir as hir;
use rustc_index::bit_set::GrowableBitSet; use rustc_index::bit_set::GrowableBitSet;
use rustc_span::symbol::sym; use rustc_span::symbol::sym;
@ -53,6 +52,8 @@ use std::iter;
use std::rc::Rc; use std::rc::Rc;
use syntax::{ast, attr}; use syntax::{ast, attr};
pub use rustc::traits::types::select::*;
pub struct SelectionContext<'cx, 'tcx> { pub struct SelectionContext<'cx, 'tcx> {
infcx: &'cx InferCtxt<'cx, 'tcx>, infcx: &'cx InferCtxt<'cx, 'tcx>,
@ -181,146 +182,6 @@ struct TraitObligationStack<'prev, 'tcx> {
dfn: usize, dfn: usize,
} }
#[derive(Clone, Default)]
pub struct SelectionCache<'tcx> {
hashmap: Lock<
FxHashMap<
ty::ParamEnvAnd<'tcx, ty::TraitRef<'tcx>>,
WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>,
>,
>,
}
/// The selection process begins by considering all impls, where
/// clauses, and so forth that might resolve an obligation. Sometimes
/// we'll be able to say definitively that (e.g.) an impl does not
/// apply to the obligation: perhaps it is defined for `usize` but the
/// obligation is for `int`. In that case, we drop the impl out of the
/// list. But the other cases are considered *candidates*.
///
/// For selection to succeed, there must be exactly one matching
/// candidate. If the obligation is fully known, this is guaranteed
/// by coherence. However, if the obligation contains type parameters
/// or variables, there may be multiple such impls.
///
/// It is not a real problem if multiple matching impls exist because
/// of type variables - it just means the obligation isn't sufficiently
/// elaborated. In that case we report an ambiguity, and the caller can
/// try again after more type information has been gathered or report a
/// "type annotations needed" error.
///
/// However, with type parameters, this can be a real problem - type
/// parameters don't unify with regular types, but they *can* unify
/// with variables from blanket impls, and (unless we know its bounds
/// will always be satisfied) picking the blanket impl will be wrong
/// for at least *some* substitutions. To make this concrete, if we have
///
/// trait AsDebug { type Out : fmt::Debug; fn debug(self) -> Self::Out; }
/// impl<T: fmt::Debug> AsDebug for T {
/// type Out = T;
/// fn debug(self) -> fmt::Debug { self }
/// }
/// fn foo<T: AsDebug>(t: T) { println!("{:?}", <T as AsDebug>::debug(t)); }
///
/// we can't just use the impl to resolve the `<T as AsDebug>` obligation
/// -- a type from another crate (that doesn't implement `fmt::Debug`) could
/// implement `AsDebug`.
///
/// Because where-clauses match the type exactly, multiple clauses can
/// only match if there are unresolved variables, and we can mostly just
/// report this ambiguity in that case. This is still a problem - we can't
/// *do anything* with ambiguities that involve only regions. This is issue
/// #21974.
///
/// If a single where-clause matches and there are no inference
/// variables left, then it definitely matches and we can just select
/// it.
///
/// In fact, we even select the where-clause when the obligation contains
/// inference variables. The can lead to inference making "leaps of logic",
/// for example in this situation:
///
/// pub trait Foo<T> { fn foo(&self) -> T; }
/// impl<T> Foo<()> for T { fn foo(&self) { } }
/// impl Foo<bool> for bool { fn foo(&self) -> bool { *self } }
///
/// pub fn foo<T>(t: T) where T: Foo<bool> {
/// println!("{:?}", <T as Foo<_>>::foo(&t));
/// }
/// fn main() { foo(false); }
///
/// Here the obligation `<T as Foo<$0>>` can be matched by both the blanket
/// impl and the where-clause. We select the where-clause and unify `$0=bool`,
/// so the program prints "false". However, if the where-clause is omitted,
/// the blanket impl is selected, we unify `$0=()`, and the program prints
/// "()".
///
/// Exactly the same issues apply to projection and object candidates, except
/// that we can have both a projection candidate and a where-clause candidate
/// for the same obligation. In that case either would do (except that
/// different "leaps of logic" would occur if inference variables are
/// present), and we just pick the where-clause. This is, for example,
/// required for associated types to work in default impls, as the bounds
/// are visible both as projection bounds and as where-clauses from the
/// parameter environment.
#[derive(PartialEq, Eq, Debug, Clone, TypeFoldable)]
enum SelectionCandidate<'tcx> {
BuiltinCandidate {
/// `false` if there are no *further* obligations.
has_nested: bool,
},
ParamCandidate(ty::PolyTraitRef<'tcx>),
ImplCandidate(DefId),
AutoImplCandidate(DefId),
/// This is a trait matching with a projected type as `Self`, and
/// we found an applicable bound in the trait definition.
ProjectionCandidate,
/// Implementation of a `Fn`-family trait by one of the anonymous types
/// generated for a `||` expression.
ClosureCandidate,
/// Implementation of a `Generator` trait by one of the anonymous types
/// generated for a generator.
GeneratorCandidate,
/// Implementation of a `Fn`-family trait by one of the anonymous
/// types generated for a fn pointer type (e.g., `fn(int) -> int`)
FnPointerCandidate,
TraitAliasCandidate(DefId),
ObjectCandidate,
BuiltinObjectCandidate,
BuiltinUnsizeCandidate,
}
impl<'a, 'tcx> ty::Lift<'tcx> for SelectionCandidate<'a> {
type Lifted = SelectionCandidate<'tcx>;
fn lift_to_tcx(&self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
Some(match *self {
BuiltinCandidate { has_nested } => BuiltinCandidate { has_nested },
ImplCandidate(def_id) => ImplCandidate(def_id),
AutoImplCandidate(def_id) => AutoImplCandidate(def_id),
ProjectionCandidate => ProjectionCandidate,
ClosureCandidate => ClosureCandidate,
GeneratorCandidate => GeneratorCandidate,
FnPointerCandidate => FnPointerCandidate,
TraitAliasCandidate(def_id) => TraitAliasCandidate(def_id),
ObjectCandidate => ObjectCandidate,
BuiltinObjectCandidate => BuiltinObjectCandidate,
BuiltinUnsizeCandidate => BuiltinUnsizeCandidate,
ParamCandidate(ref trait_ref) => {
return tcx.lift(trait_ref).map(ParamCandidate);
}
})
}
}
struct SelectionCandidateSet<'tcx> { struct SelectionCandidateSet<'tcx> {
// A list of candidates that definitely apply to the current // A list of candidates that definitely apply to the current
// obligation (meaning: types unify). // obligation (meaning: types unify).
@ -350,134 +211,6 @@ enum BuiltinImplConditions<'tcx> {
Ambiguous, Ambiguous,
} }
/// The result of trait evaluation. The order is important
/// here as the evaluation of a list is the maximum of the
/// evaluations.
///
/// The evaluation results are ordered:
/// - `EvaluatedToOk` implies `EvaluatedToOkModuloRegions`
/// implies `EvaluatedToAmbig` implies `EvaluatedToUnknown`
/// - `EvaluatedToErr` implies `EvaluatedToRecur`
/// - the "union" of evaluation results is equal to their maximum -
/// all the "potential success" candidates can potentially succeed,
/// so they are noops when unioned with a definite error, and within
/// the categories it's easy to see that the unions are correct.
#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, HashStable)]
pub enum EvaluationResult {
/// Evaluation successful.
EvaluatedToOk,
/// Evaluation successful, but there were unevaluated region obligations.
EvaluatedToOkModuloRegions,
/// Evaluation is known to be ambiguous -- it *might* hold for some
/// assignment of inference variables, but it might not.
///
/// While this has the same meaning as `EvaluatedToUnknown` -- we can't
/// know whether this obligation holds or not -- it is the result we
/// would get with an empty stack, and therefore is cacheable.
EvaluatedToAmbig,
/// Evaluation failed because of recursion involving inference
/// variables. We are somewhat imprecise there, so we don't actually
/// know the real result.
///
/// This can't be trivially cached for the same reason as `EvaluatedToRecur`.
EvaluatedToUnknown,
/// Evaluation failed because we encountered an obligation we are already
/// trying to prove on this branch.
///
/// We know this branch can't be a part of a minimal proof-tree for
/// the "root" of our cycle, because then we could cut out the recursion
/// and maintain a valid proof tree. However, this does not mean
/// that all the obligations on this branch do not hold -- it's possible
/// that we entered this branch "speculatively", and that there
/// might be some other way to prove this obligation that does not
/// go through this cycle -- so we can't cache this as a failure.
///
/// For example, suppose we have this:
///
/// ```rust,ignore (pseudo-Rust)
/// pub trait Trait { fn xyz(); }
/// // This impl is "useless", but we can still have
/// // an `impl Trait for SomeUnsizedType` somewhere.
/// impl<T: Trait + Sized> Trait for T { fn xyz() {} }
///
/// pub fn foo<T: Trait + ?Sized>() {
/// <T as Trait>::xyz();
/// }
/// ```
///
/// When checking `foo`, we have to prove `T: Trait`. This basically
/// translates into this:
///
/// ```plain,ignore
/// (T: Trait + Sized →_\impl T: Trait), T: Trait ⊢ T: Trait
/// ```
///
/// When we try to prove it, we first go the first option, which
/// recurses. This shows us that the impl is "useless" -- it won't
/// tell us that `T: Trait` unless it already implemented `Trait`
/// by some other means. However, that does not prevent `T: Trait`
/// does not hold, because of the bound (which can indeed be satisfied
/// by `SomeUnsizedType` from another crate).
//
// FIXME: when an `EvaluatedToRecur` goes past its parent root, we
// ought to convert it to an `EvaluatedToErr`, because we know
// there definitely isn't a proof tree for that obligation. Not
// doing so is still sound -- there isn't any proof tree, so the
// branch still can't be a part of a minimal one -- but does not re-enable caching.
EvaluatedToRecur,
/// Evaluation failed.
EvaluatedToErr,
}
impl EvaluationResult {
/// Returns `true` if this evaluation result is known to apply, even
/// considering outlives constraints.
pub fn must_apply_considering_regions(self) -> bool {
self == EvaluatedToOk
}
/// Returns `true` if this evaluation result is known to apply, ignoring
/// outlives constraints.
pub fn must_apply_modulo_regions(self) -> bool {
self <= EvaluatedToOkModuloRegions
}
pub fn may_apply(self) -> bool {
match self {
EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToUnknown => {
true
}
EvaluatedToErr | EvaluatedToRecur => false,
}
}
fn is_stack_dependent(self) -> bool {
match self {
EvaluatedToUnknown | EvaluatedToRecur => true,
EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToErr => false,
}
}
}
/// Indicates that trait evaluation caused overflow.
#[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable)]
pub struct OverflowError;
impl<'tcx> From<OverflowError> for SelectionError<'tcx> {
fn from(OverflowError: OverflowError) -> SelectionError<'tcx> {
SelectionError::Overflow
}
}
#[derive(Clone, Default)]
pub struct EvaluationCache<'tcx> {
hashmap: Lock<
FxHashMap<ty::ParamEnvAnd<'tcx, ty::PolyTraitRef<'tcx>>, WithDepNode<EvaluationResult>>,
>,
}
impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
pub fn new(infcx: &'cx InferCtxt<'cx, 'tcx>) -> SelectionContext<'cx, 'tcx> { pub fn new(infcx: &'cx InferCtxt<'cx, 'tcx>) -> SelectionContext<'cx, 'tcx> {
SelectionContext { SelectionContext {
@ -3827,13 +3560,6 @@ impl<'tcx> TraitObligation<'tcx> {
} }
} }
impl<'tcx> SelectionCache<'tcx> {
/// Actually frees the underlying memory in contrast to what stdlib containers do on `clear`
pub fn clear(&self) {
*self.hashmap.borrow_mut() = Default::default();
}
}
impl<'tcx> EvaluationCache<'tcx> { impl<'tcx> EvaluationCache<'tcx> {
/// Actually frees the underlying memory in contrast to what stdlib containers do on `clear` /// Actually frees the underlying memory in contrast to what stdlib containers do on `clear`
pub fn clear(&self) { pub fn clear(&self) {
@ -4126,20 +3852,3 @@ impl<'o, 'tcx> fmt::Debug for TraitObligationStack<'o, 'tcx> {
write!(f, "TraitObligationStack({:?})", self.obligation) write!(f, "TraitObligationStack({:?})", self.obligation)
} }
} }
#[derive(Clone, Eq, PartialEq)]
pub struct WithDepNode<T> {
dep_node: DepNodeIndex,
cached_value: T,
}
impl<T: Clone> WithDepNode<T> {
pub fn new(dep_node: DepNodeIndex, cached_value: T) -> Self {
WithDepNode { dep_node, cached_value }
}
pub fn get(&self, tcx: TyCtxt<'_>) -> T {
tcx.dep_graph.read_index(self.dep_node);
self.cached_value.clone()
}
}

4
src/librustc/traits/types/mod.rs
View File

@ -2,6 +2,8 @@
//! //!
//! [rustc guide]: https://rust-lang.github.io/rustc-guide/traits/resolution.html //! [rustc guide]: https://rust-lang.github.io/rustc-guide/traits/resolution.html
pub mod select;
use crate::mir::interpret::ErrorHandled; use crate::mir::interpret::ErrorHandled;
use crate::ty::fold::{TypeFolder, TypeVisitor}; use crate::ty::fold::{TypeFolder, TypeVisitor};
use crate::ty::subst::SubstsRef; use crate::ty::subst::SubstsRef;
@ -15,6 +17,8 @@ use syntax::ast;
use std::fmt::Debug; use std::fmt::Debug;
use std::rc::Rc; use std::rc::Rc;
pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
pub use self::ObligationCauseCode::*; pub use self::ObligationCauseCode::*;
pub use self::SelectionError::*; pub use self::SelectionError::*;
pub use self::Vtable::*; pub use self::Vtable::*;

283
src/librustc/traits/types/select.rs Normal file
View File

@ -0,0 +1,283 @@
//! Candidate selection. See the [rustc guide] for more information on how this works.
//!
//! [rustc guide]: https://rust-lang.github.io/rustc-guide/traits/resolution.html#selection
use self::EvaluationResult::*;
use super::{SelectionError, SelectionResult};
use crate::dep_graph::DepNodeIndex;
use crate::ty::{self, TyCtxt};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lock;
use rustc_hir::def_id::DefId;
#[derive(Clone, Default)]
pub struct SelectionCache<'tcx> {
pub hashmap: Lock<
FxHashMap<
ty::ParamEnvAnd<'tcx, ty::TraitRef<'tcx>>,
WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>,
>,
>,
}
impl<'tcx> SelectionCache<'tcx> {
/// Actually frees the underlying memory in contrast to what stdlib containers do on `clear`
pub fn clear(&self) {
*self.hashmap.borrow_mut() = Default::default();
}
}
/// The selection process begins by considering all impls, where
/// clauses, and so forth that might resolve an obligation. Sometimes
/// we'll be able to say definitively that (e.g.) an impl does not
/// apply to the obligation: perhaps it is defined for `usize` but the
/// obligation is for `int`. In that case, we drop the impl out of the
/// list. But the other cases are considered *candidates*.
///
/// For selection to succeed, there must be exactly one matching
/// candidate. If the obligation is fully known, this is guaranteed
/// by coherence. However, if the obligation contains type parameters
/// or variables, there may be multiple such impls.
///
/// It is not a real problem if multiple matching impls exist because
/// of type variables - it just means the obligation isn't sufficiently
/// elaborated. In that case we report an ambiguity, and the caller can
/// try again after more type information has been gathered or report a
/// "type annotations needed" error.
///
/// However, with type parameters, this can be a real problem - type
/// parameters don't unify with regular types, but they *can* unify
/// with variables from blanket impls, and (unless we know its bounds
/// will always be satisfied) picking the blanket impl will be wrong
/// for at least *some* substitutions. To make this concrete, if we have
///
/// trait AsDebug { type Out : fmt::Debug; fn debug(self) -> Self::Out; }
/// impl<T: fmt::Debug> AsDebug for T {
/// type Out = T;
/// fn debug(self) -> fmt::Debug { self }
/// }
/// fn foo<T: AsDebug>(t: T) { println!("{:?}", <T as AsDebug>::debug(t)); }
///
/// we can't just use the impl to resolve the `<T as AsDebug>` obligation
/// -- a type from another crate (that doesn't implement `fmt::Debug`) could
/// implement `AsDebug`.
///
/// Because where-clauses match the type exactly, multiple clauses can
/// only match if there are unresolved variables, and we can mostly just
/// report this ambiguity in that case. This is still a problem - we can't
/// *do anything* with ambiguities that involve only regions. This is issue
/// #21974.
///
/// If a single where-clause matches and there are no inference
/// variables left, then it definitely matches and we can just select
/// it.
///
/// In fact, we even select the where-clause when the obligation contains
/// inference variables. The can lead to inference making "leaps of logic",
/// for example in this situation:
///
/// pub trait Foo<T> { fn foo(&self) -> T; }
/// impl<T> Foo<()> for T { fn foo(&self) { } }
/// impl Foo<bool> for bool { fn foo(&self) -> bool { *self } }
///
/// pub fn foo<T>(t: T) where T: Foo<bool> {
/// println!("{:?}", <T as Foo<_>>::foo(&t));
/// }
/// fn main() { foo(false); }
///
/// Here the obligation `<T as Foo<$0>>` can be matched by both the blanket
/// impl and the where-clause. We select the where-clause and unify `$0=bool`,
/// so the program prints "false". However, if the where-clause is omitted,
/// the blanket impl is selected, we unify `$0=()`, and the program prints
/// "()".
///
/// Exactly the same issues apply to projection and object candidates, except
/// that we can have both a projection candidate and a where-clause candidate
/// for the same obligation. In that case either would do (except that
/// different "leaps of logic" would occur if inference variables are
/// present), and we just pick the where-clause. This is, for example,
/// required for associated types to work in default impls, as the bounds
/// are visible both as projection bounds and as where-clauses from the
/// parameter environment.
#[derive(PartialEq, Eq, Debug, Clone, TypeFoldable)]
pub enum SelectionCandidate<'tcx> {
BuiltinCandidate {
/// `false` if there are no *further* obligations.
has_nested: bool,
},
ParamCandidate(ty::PolyTraitRef<'tcx>),
ImplCandidate(DefId),
AutoImplCandidate(DefId),
/// This is a trait matching with a projected type as `Self`, and
/// we found an applicable bound in the trait definition.
ProjectionCandidate,
/// Implementation of a `Fn`-family trait by one of the anonymous types
/// generated for a `||` expression.
ClosureCandidate,
/// Implementation of a `Generator` trait by one of the anonymous types
/// generated for a generator.
GeneratorCandidate,
/// Implementation of a `Fn`-family trait by one of the anonymous
/// types generated for a fn pointer type (e.g., `fn(int) -> int`)
FnPointerCandidate,
TraitAliasCandidate(DefId),
ObjectCandidate,
BuiltinObjectCandidate,
BuiltinUnsizeCandidate,
}
/// The result of trait evaluation. The order is important
/// here as the evaluation of a list is the maximum of the
/// evaluations.
///
/// The evaluation results are ordered:
/// - `EvaluatedToOk` implies `EvaluatedToOkModuloRegions`
/// implies `EvaluatedToAmbig` implies `EvaluatedToUnknown`
/// - `EvaluatedToErr` implies `EvaluatedToRecur`
/// - the "union" of evaluation results is equal to their maximum -
/// all the "potential success" candidates can potentially succeed,
/// so they are noops when unioned with a definite error, and within
/// the categories it's easy to see that the unions are correct.
#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, HashStable)]
pub enum EvaluationResult {
/// Evaluation successful.
EvaluatedToOk,
/// Evaluation successful, but there were unevaluated region obligations.
EvaluatedToOkModuloRegions,
/// Evaluation is known to be ambiguous -- it *might* hold for some
/// assignment of inference variables, but it might not.
///
/// While this has the same meaning as `EvaluatedToUnknown` -- we can't
/// know whether this obligation holds or not -- it is the result we
/// would get with an empty stack, and therefore is cacheable.
EvaluatedToAmbig,
/// Evaluation failed because of recursion involving inference
/// variables. We are somewhat imprecise there, so we don't actually
/// know the real result.
///
/// This can't be trivially cached for the same reason as `EvaluatedToRecur`.
EvaluatedToUnknown,
/// Evaluation failed because we encountered an obligation we are already
/// trying to prove on this branch.
///
/// We know this branch can't be a part of a minimal proof-tree for
/// the "root" of our cycle, because then we could cut out the recursion
/// and maintain a valid proof tree. However, this does not mean
/// that all the obligations on this branch do not hold -- it's possible
/// that we entered this branch "speculatively", and that there
/// might be some other way to prove this obligation that does not
/// go through this cycle -- so we can't cache this as a failure.
///
/// For example, suppose we have this:
///
/// ```rust,ignore (pseudo-Rust)
/// pub trait Trait { fn xyz(); }
/// // This impl is "useless", but we can still have
/// // an `impl Trait for SomeUnsizedType` somewhere.
/// impl<T: Trait + Sized> Trait for T { fn xyz() {} }
///
/// pub fn foo<T: Trait + ?Sized>() {
/// <T as Trait>::xyz();
/// }
/// ```
///
/// When checking `foo`, we have to prove `T: Trait`. This basically
/// translates into this:
///
/// ```plain,ignore
/// (T: Trait + Sized →_\impl T: Trait), T: Trait ⊢ T: Trait
/// ```
///
/// When we try to prove it, we first go the first option, which
/// recurses. This shows us that the impl is "useless" -- it won't
/// tell us that `T: Trait` unless it already implemented `Trait`
/// by some other means. However, that does not prevent `T: Trait`
/// does not hold, because of the bound (which can indeed be satisfied
/// by `SomeUnsizedType` from another crate).
//
// FIXME: when an `EvaluatedToRecur` goes past its parent root, we
// ought to convert it to an `EvaluatedToErr`, because we know
// there definitely isn't a proof tree for that obligation. Not
// doing so is still sound -- there isn't any proof tree, so the
// branch still can't be a part of a minimal one -- but does not re-enable caching.
EvaluatedToRecur,
/// Evaluation failed.
EvaluatedToErr,
}
impl EvaluationResult {
/// Returns `true` if this evaluation result is known to apply, even
/// considering outlives constraints.
pub fn must_apply_considering_regions(self) -> bool {
self == EvaluatedToOk
}
/// Returns `true` if this evaluation result is known to apply, ignoring
/// outlives constraints.
pub fn must_apply_modulo_regions(self) -> bool {
self <= EvaluatedToOkModuloRegions
}
pub fn may_apply(self) -> bool {
match self {
EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToUnknown => {
true
}
EvaluatedToErr | EvaluatedToRecur => false,
}
}
pub fn is_stack_dependent(self) -> bool {
match self {
EvaluatedToUnknown | EvaluatedToRecur => true,
EvaluatedToOk | EvaluatedToOkModuloRegions | EvaluatedToAmbig | EvaluatedToErr => false,
}
}
}
/// Indicates that trait evaluation caused overflow.
#[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable)]
pub struct OverflowError;
impl<'tcx> From<OverflowError> for SelectionError<'tcx> {
fn from(OverflowError: OverflowError) -> SelectionError<'tcx> {
SelectionError::Overflow
}
}
#[derive(Clone, Default)]
pub struct EvaluationCache<'tcx> {
pub hashmap: Lock<
FxHashMap<ty::ParamEnvAnd<'tcx, ty::PolyTraitRef<'tcx>>, WithDepNode<EvaluationResult>>,
>,
}
#[derive(Clone, Eq, PartialEq)]
pub struct WithDepNode<T> {
dep_node: DepNodeIndex,
cached_value: T,
}
impl<T: Clone> WithDepNode<T> {
pub fn new(dep_node: DepNodeIndex, cached_value: T) -> Self {
WithDepNode { dep_node, cached_value }
}
pub fn get(&self, tcx: TyCtxt<'_>) -> T {
tcx.dep_graph.read_index(self.dep_node);
self.cached_value.clone()
}
}