[−][src]Trait rustc_mir::transform::check_consts::qualifs::Qualif

pub trait Qualif {
    pub const ANALYSIS_NAME: &'static str;
    pub const IS_CLEARED_ON_MOVE: bool;

    pub fn in_qualifs(qualifs: &ConstQualifs) -> bool;

    pub fn in_any_value_of_ty<'tcx>(
        cx: &ConstCx<'_, 'tcx>, 
        ty: Ty<'tcx>
    ) -> bool;

    pub fn in_adt_inherently<'tcx>(
        cx: &ConstCx<'_, 'tcx>, 
        adt: &'tcx AdtDef, 
        substs: SubstsRef<'tcx>
    ) -> bool;
}

A "qualif"(-ication) is a way to look for something "bad" in the MIR that would disqualify some code for promotion or prevent it from evaluating at compile time.

Normally, we would determine what qualifications apply to each type and error when an illegal operation is performed on such a type. However, this was found to be too imprecise, especially in the presence of enums. If only a single variant of an enum has a certain qualification, we needn't reject code unless it actually constructs and operates on the qualifed variant.

To accomplish this, const-checking and promotion use a value-based analysis (as opposed to a type-based one). Qualifications propagate structurally across variables: If a local (or a projection of a local) is assigned a qualifed value, that local itself becomes qualifed.

Associated Constants

pub const ANALYSIS_NAME: &'static str[src]

The name of the file used to debug the dataflow analysis that computes this qualif.

pub const IS_CLEARED_ON_MOVE: bool[src]

Whether this Qualif is cleared when a local is moved from.

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Required methods

pub fn in_qualifs(qualifs: &ConstQualifs) -> bool[src]

Extracts the field of ConstQualifs that corresponds to this Qualif.

pub fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> bool[src]

Returns true if any value of the given type could possibly have this Qualif.

This function determines Qualifs when we cannot do a value-based analysis. Since qualif propagation is context-insenstive, this includes function arguments and values returned from a call to another function.

It also determines the Qualifs for primitive types.

pub fn in_adt_inherently<'tcx>(
    cx: &ConstCx<'_, 'tcx>,
    adt: &'tcx AdtDef,
    substs: SubstsRef<'tcx>
) -> bool[src]

Returns true if this Qualif is inherent to the given struct or enum.

By default, Qualifs propagate into ADTs in a structural way: An ADT only becomes qualified if part of it is assigned a value with that Qualif. However, some ADTs always have a certain Qualif, regardless of whether their fields have it. For example, a type with a custom Drop impl is inherently NeedsDrop.

Returning true for in_adt_inherently but false for in_any_value_of_ty is unsound.

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Implementors

impl Qualif for CustomEq[src]

impl Qualif for HasMutInterior[src]

impl Qualif for NeedsDrop[src]

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