Enum rustc_middle::mir::FakeReadCause

pub enum FakeReadCause {
    ForMatchGuard,
    ForMatchedPlace,
    ForGuardBinding,
    ForLet,
    ForIndex,
}

The FakeReadCause describes the type of pattern why a FakeRead statement exists.

Variants

ForMatchGuard

Inject a fake read of the borrowed input at the end of each guards code.

This should ensure that you cannot change the variant for an enum while you are in the midst of matching on it.

ForMatchedPlace

let x: !; match x {} doesn't generate any read of x so we need to generate a read of x to check that it is initialized and safe.

ForGuardBinding

A fake read of the RefWithinGuard version of a bind-by-value variable in a match guard to ensure that it's value hasn't change by the time we create the OutsideGuard version.

ForLet

Officially, the semantics of

let pattern = <expr>;

is that <expr> is evaluated into a temporary and then this temporary is into the pattern.

However, if we see the simple pattern let var = <expr>, we optimize this to evaluate <expr> directly into the variable var. This is mostly unobservable, but in some cases it can affect the borrow checker, as in #53695. Therefore, we insert a "fake read" here to ensure that we get appropriate errors.

ForIndex

If we have an index expression like

(*x)[1][{ x = y; 4}]

then the first bounds check is invalidated when we evaluate the second index expression. Thus we create a fake borrow of x across the second indexer, which will cause a borrow check error.

Trait Implementations

impl Clone for FakeReadCause

pub fn clone(&self) -> FakeReadCause

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Copy for FakeReadCause

impl Debug for FakeReadCause

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

Formats the value using the given formatter.

impl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for FakeReadCause

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

impl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for FakeReadCause

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

impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for FakeReadCause

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

impl<'tcx> Lift<'tcx> for FakeReadCause

type Lifted = Self

pub fn lift_to_tcx(self, _: TyCtxt<'tcx>) -> Option<Self>

impl PartialEq<FakeReadCause> for FakeReadCause

pub fn eq(&self, other: &FakeReadCause) -> bool

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

#[must_use]pub fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl StructuralPartialEq for FakeReadCause

impl<'tcx> TypeFoldable<'tcx> for FakeReadCause

pub fn super_fold_with<F: TypeFolder<'tcx>>(self, _: &mut F) -> FakeReadCause

pub fn super_visit_with<F: TypeVisitor<'tcx>>(
    &self,
    _: &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.