Function rustc_mir::borrow_check::type_check::relate_tys::relate_types

pub(in borrow_check::type_check) fn relate_types<'tcx>(
    infcx: &InferCtxt<'_, 'tcx>, 
    a: Ty<'tcx>, 
    v: Variance, 
    b: Ty<'tcx>, 
    locations: Locations, 
    category: ConstraintCategory, 
    borrowck_context: Option<&mut BorrowCheckContext<'_, 'tcx>>
) -> Fallible<()>

Adds sufficient constraints to ensure that a R b where R depends on v:

• "Covariant" a <: b
• "Invariant" a == b
• "Contravariant" a :> b

N.B., the type a is permitted to have unresolved inference variables, but not the type b.