Struct rustc_infer::infer::nll_relate::TypeRelating

pub struct TypeRelating<'me, 'tcx, D>where
    D: TypeRelatingDelegate<'tcx>,{
    infcx: &'me InferCtxt<'tcx>,
    delegate: D,
    ambient_variance: Variance,
    ambient_variance_info: VarianceDiagInfo<'tcx>,
    a_scopes: Vec<BoundRegionScope<'tcx>>,
    b_scopes: Vec<BoundRegionScope<'tcx>>,
}

Fields

infcx: &'me InferCtxt<'tcx>

delegate: D

Callback to use when we deduce an outlives relationship.

ambient_variance: Variance

How are we relating a and b?

• Covariant means a <: b.
• Contravariant means b <: a.
• Invariant means `a == b.
• Bivariant means that it doesn’t matter.

ambient_variance_info: VarianceDiagInfo<'tcx>

a_scopes: Vec<BoundRegionScope<'tcx>>

When we pass through a set of binders (e.g., when looking into a fn type), we push a new bound region scope onto here. This will contain the instantiated region for each region in those binders. When we then encounter a ReLateBound(d, br), we can use the De Bruijn index d to find the right scope, and then bound region name br to find the specific instantiation from within that scope. See replace_bound_region.

This field stores the instantiations for late-bound regions in the a type.

b_scopes: Vec<BoundRegionScope<'tcx>>

Same as a_scopes, but for the b type.

Implementations

impl<'me, 'tcx, D> TypeRelating<'me, 'tcx, D>where
    D: TypeRelatingDelegate<'tcx>,

pub fn new(
    infcx: &'me InferCtxt<'tcx>,
    delegate: D,
    ambient_variance: Variance
) -> Self

fn ambient_covariance(&self) -> bool

fn ambient_contravariance(&self) -> bool

fn create_scope(
    &mut self,
    value: Binder<'tcx, impl Relate<'tcx>>,
    universally_quantified: UniversallyQuantified
) -> BoundRegionScope<'tcx>

fn lookup_bound_region(
    debruijn: DebruijnIndex,
    br: &BoundRegion,
    first_free_index: DebruijnIndex,
    scopes: &[BoundRegionScope<'tcx>]
) -> Region<'tcx>

When we encounter binders during the type traversal, we record the value to substitute for each of the things contained in that binder. (This will be either a universal placeholder or an existential inference variable.) Given the De Bruijn index debruijn (and name br) of some binder we have now encountered, this routine finds the value that we instantiated the region with; to do so, it indexes backwards into the list of ambient scopes scopes.

fn replace_bound_region(
    &self,
    r: Region<'tcx>,
    first_free_index: DebruijnIndex,
    scopes: &[BoundRegionScope<'tcx>]
) -> Region<'tcx>

If r is a bound region, find the scope in which it is bound (from scopes) and return the value that we instantiated it with. Otherwise just return r.

fn push_outlives(
    &mut self,
    sup: Region<'tcx>,
    sub: Region<'tcx>,
    info: VarianceDiagInfo<'tcx>
)

Push a new outlives requirement into our output set of constraints.

fn relate_projection_ty(
    &mut self,
    projection_ty: AliasTy<'tcx>,
    value_ty: Ty<'tcx>
) -> Ty<'tcx>

Relate a projection type and some value type lazily. This will always succeed, but we push an additional ProjectionEq goal depending on the value type:

• if the value type is any type T which is not a projection, we push ProjectionEq(projection = T).
• if the value type is another projection other_projection, we create a new inference variable ?U and push the two goals ProjectionEq(projection = ?U), ProjectionEq(other_projection = ?U).

fn relate_ty_var<PAIR: VidValuePair<'tcx>>(
    &mut self,
    pair: PAIR
) -> RelateResult<'tcx, Ty<'tcx>>

Relate a type inference variable with a value type. This works by creating a “generalization” G of the value where all the lifetimes are replaced with fresh inference values. This generalization G becomes the value of the inference variable, and is then related in turn to the value. So e.g. if you had vid = ?0 and value = &'a u32, we might first instantiate ?0 to a type like &'0 u32 where '0 is a fresh variable, and then relate &'0 u32 with &'a u32 (resulting in relations between '0 and 'a).

The variable pair can be either a (vid, ty) or (ty, vid) – in other words, it is always an (unresolved) inference variable vid and a type ty that are being related, but the vid may appear either as the “a” type or the “b” type, depending on where it appears in the tuple. The trait VidValuePair lets us work with the vid/type while preserving the “sidedness” when necessary – the sidedness is relevant in particular for the variance and set of in-scope things.

fn generalize_value<T: Relate<'tcx>>(
    &mut self,
    value: T,
    for_vid: TyVid
) -> RelateResult<'tcx, T>

fn relate_opaques(
    &mut self,
    a: Ty<'tcx>,
    b: Ty<'tcx>
) -> RelateResult<'tcx, Ty<'tcx>>

Trait Implementations

impl<'tcx, D> ConstEquateRelation<'tcx> for TypeRelating<'_, 'tcx, D>where
    D: TypeRelatingDelegate<'tcx>,

fn const_equate_obligation(&mut self, _a: Const<'tcx>, _b: Const<'tcx>)

Register an obligation that both constants must be equal to each other.

impl<'tcx, D> TypeRelation<'tcx> for TypeRelating<'_, 'tcx, D>where
    D: TypeRelatingDelegate<'tcx>,

fn tcx(&self) -> TyCtxt<'tcx>

fn intercrate(&self) -> bool

fn param_env(&self) -> ParamEnv<'tcx>

fn tag(&self) -> &'static str

Returns a static string we can use for printouts.

fn a_is_expected(&self) -> bool

Returns true if the value a is the “expected” type in the relation. Just affects error messages.

fn mark_ambiguous(&mut self)

Used during coherence. If called, must emit an always-ambiguous obligation.

fn relate_with_variance<T: Relate<'tcx>>(
    &mut self,
    variance: Variance,
    info: VarianceDiagInfo<'tcx>,
    a: T,
    b: T
) -> RelateResult<'tcx, T>

Switch variance for the purpose of relating a and b.

fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>>

fn regions(
    &mut self,
    a: Region<'tcx>,
    b: Region<'tcx>
) -> RelateResult<'tcx, Region<'tcx>>

fn consts(
    &mut self,
    a: Const<'tcx>,
    b: Const<'tcx>
) -> RelateResult<'tcx, Const<'tcx>>

fn binders<T>(
    &mut self,
    a: Binder<'tcx, T>,
    b: Binder<'tcx, T>
) -> RelateResult<'tcx, Binder<'tcx, T>>where
    T: Relate<'tcx>,

fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> Rwhere
    F: FnOnce(&mut Self) -> R,

fn relate<T>(&mut self, a: T, b: T) -> Result<T, TypeError<'tcx>>where
    T: Relate<'tcx>,

Generic relation routine suitable for most anything.

fn relate_item_substs(
    &mut self,
    item_def_id: DefId,
    a_subst: &'tcx List<GenericArg<'tcx>>,
    b_subst: &'tcx List<GenericArg<'tcx>>
) -> Result<&'tcx List<GenericArg<'tcx>>, TypeError<'tcx>>

Relate the two substitutions for the given item. The default is to look up the variance for the item and proceed accordingly.

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.