Struct rustc_middle::ty::WithOptConstParam

pub struct WithOptConstParam<T> {
    pub did: T,
    pub const_param_did: Option<DefId>,
}

A DefId which, in case it is a const argument, is potentially bundled with the DefId of the generic parameter it instantiates.

This is used to avoid calls to type_of for const arguments during typeck which cause cycle errors.

struct A;
impl A {
    fn foo<const N: usize>(&self) -> [u8; N] { [0; N] }
    //           ^ const parameter
}
struct B;
impl B {
    fn foo<const M: u8>(&self) -> usize { 42 }
    //           ^ const parameter
}

fn main() {
    let a = A;
    let _b = a.foo::<{ 3 + 7 }>();
    //               ^^^^^^^^^ const argument
}

Let's look at the call a.foo::<{ 3 + 7 }>() here. We do not know which foo is used until we know the type of a.

We only know the type of a once we are inside of typeck(main). We also end up normalizing the type of _b during typeck(main) which requires us to evaluate the const argument.

To evaluate that const argument we need to know its type, which we would get using type_of(const_arg). This requires us to resolve foo as it can be either usize or u8 in this example. However, resolving foo once again requires typeck(main) to get the type of a, which results in a cycle.

In short we must not call type_of(const_arg) during typeck(main).

When first creating the ty::Const of the const argument inside of typeck we have already resolved foo so we know which const parameter this argument instantiates. This means that we also know the expected result of type_of(const_arg) even if we aren't allowed to call that query: it is equal to type_of(const_param) which is trivial to compute.

If we now want to use that constant in a place which potentionally needs its type we also pass the type of its const_param. This is the point of WithOptConstParam, except that instead of a Ty we bundle the DefId of the const parameter. Meaning that we need to use type_of(const_param_did) if const_param_did is Some to get the type of did.

Fields

did: T

const_param_did: Option<DefId>

The DefId of the corresponding generic parameter in case did is a const argument.

Note that even if did is a const argument, this may still be None. All queries taking WithOptConstParam start by calling tcx.opt_const_param_of(def.did) to potentially update param_did in the case it is None.

Implementations

impl<T> WithOptConstParam<T>

pub fn unknown(did: T) -> WithOptConstParam<T>

Creates a new WithOptConstParam setting const_param_did to None.

impl WithOptConstParam<LocalDefId>

pub fn try_lookup(
    did: LocalDefId,
    tcx: TyCtxt<'_>
) -> Option<(LocalDefId, DefId)>

Returns Some((did, param_did)) if def_id is a const argument, None otherwise.

pub fn try_upgrade(
    self,
    tcx: TyCtxt<'_>
) -> Option<WithOptConstParam<LocalDefId>>

In case self is unknown but self.did is a const argument, this returns a WithOptConstParam with the correct const_param_did.

pub fn to_global(self) -> WithOptConstParam<DefId>

pub fn def_id_for_type_of(self) -> DefId

impl WithOptConstParam<DefId>

pub fn as_local(self) -> Option<WithOptConstParam<LocalDefId>>

pub fn as_const_arg(self) -> Option<(LocalDefId, DefId)>

pub fn expect_local(self) -> WithOptConstParam<LocalDefId>

pub fn is_local(self) -> bool

pub fn def_id_for_type_of(self) -> DefId

Trait Implementations

impl<T: Clone> Clone for WithOptConstParam<T>

pub fn clone(&self) -> WithOptConstParam<T>

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Copy> Copy for WithOptConstParam<T>

impl<T: Debug> Debug for WithOptConstParam<T>

pub fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'tcx, T, __D: TyDecoder<'tcx>> Decodable<__D> for WithOptConstParam<T> where
    T: Decodable<__D>, 

pub fn decode(__decoder: &mut __D) -> Result<Self, <__D as Decoder>::Error>

impl<'tcx, T, __E: TyEncoder<'tcx>> Encodable<__E> for WithOptConstParam<T> where
    T: Encodable<__E>, 

pub fn encode(&self, __encoder: &mut __E) -> Result<(), <__E as Encoder>::Error>

impl<T: Eq> Eq for WithOptConstParam<T>

impl<T: Hash> Hash for WithOptConstParam<T>

pub fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

pub fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl<'__ctx, T> HashStable<StableHashingContext<'__ctx>> for WithOptConstParam<T> where
    T: HashStable<StableHashingContext<'__ctx>>, 

pub fn hash_stable(
    &self,
    __hcx: &mut StableHashingContext<'__ctx>,
    __hasher: &mut StableHasher
)

impl Key for WithOptConstParam<LocalDefId>

type CacheSelector = DefaultCacheSelector

pub fn query_crate(&self) -> CrateNum

Given an instance of this key, what crate is it referring to? This is used to find the provider.

pub fn default_span(&self, tcx: TyCtxt<'_>) -> Span

In the event that a cycle occurs, if no explicit span has been given for a query with key self, what span should we use?

impl<'__lifted, T> Lift<'__lifted> for WithOptConstParam<T> where
    T: Lift<'__lifted>, 

type Lifted = WithOptConstParam<T::Lifted>

pub fn lift_to_tcx(
    self,
    __tcx: TyCtxt<'__lifted>
) -> Option<WithOptConstParam<T::Lifted>>

impl<T: Ord> Ord for WithOptConstParam<T>

pub fn cmp(&self, other: &WithOptConstParam<T>) -> Ordering

This method returns an Ordering between self and other.

#[must_use]pub fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]pub fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl<T: PartialEq> PartialEq<WithOptConstParam<T>> for WithOptConstParam<T>

pub fn eq(&self, other: &WithOptConstParam<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

pub fn ne(&self, other: &WithOptConstParam<T>) -> bool

This method tests for !=.

impl<T: PartialOrd> PartialOrd<WithOptConstParam<T>> for WithOptConstParam<T>

pub fn partial_cmp(&self, other: &WithOptConstParam<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

pub fn lt(&self, other: &WithOptConstParam<T>) -> bool

This method tests less than (for self and other) and is used by the < operator.

pub fn le(&self, other: &WithOptConstParam<T>) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

pub fn gt(&self, other: &WithOptConstParam<T>) -> bool

This method tests greater than (for self and other) and is used by the > operator.

pub fn ge(&self, other: &WithOptConstParam<T>) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T: SpecIntoSelfProfilingString> SpecIntoSelfProfilingString for WithOptConstParam<T>

pub fn spec_to_self_profile_string(
    &self,
    builder: &mut QueryKeyStringBuilder<'_, '_, '_>
) -> StringId

impl<T> StructuralEq for WithOptConstParam<T>

impl<T> StructuralPartialEq for WithOptConstParam<T>

impl<T, 'tcx> TypeFoldable<'tcx> for WithOptConstParam<T> where
    T: TypeFoldable<'tcx>, 

pub fn super_fold_with<__F: TypeFolder<'tcx>>(self, __folder: &mut __F) -> Self

pub fn super_visit_with<__F: TypeVisitor<'tcx>>(
    &self,
    __folder: &mut __F
) -> ControlFlow<__F::BreakTy>

pub fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self

pub fn visit_with<V: TypeVisitor<'tcx>>(
    &self,
    visitor: &mut V
) -> ControlFlow<V::BreakTy>

pub fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns true if self has any late-bound regions that are either bound by binder or bound by some binder outside of binder. If binder is ty::INNERMOST, this indicates whether there are any late-bound regions that appear free.

pub fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns true if this self has any regions that escape binder (and hence are not bound by it).

pub fn has_escaping_bound_vars(&self) -> bool

pub fn has_type_flags(&self, flags: TypeFlags) -> bool

pub fn has_projections(&self) -> bool

pub fn has_opaque_types(&self) -> bool

pub fn references_error(&self) -> bool

pub fn has_param_types_or_consts(&self) -> bool

pub fn has_infer_regions(&self) -> bool

pub fn has_infer_types(&self) -> bool

pub fn has_infer_types_or_consts(&self) -> bool

pub fn needs_infer(&self) -> bool

pub fn has_placeholders(&self) -> bool

pub fn needs_subst(&self) -> bool

pub fn has_free_regions(&self) -> bool

"Free" regions in this context means that it has any region that is not (a) erased or (b) late-bound.

pub fn has_erased_regions(&self) -> bool

pub fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.

pub fn is_global(&self) -> bool

Indicates whether this value references only 'global' generic parameters that are the same regardless of what fn we are in. This is used for caching.

pub fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

pub fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of impl specialization.