Function is_enum_variant_uninhabited_from 

pub(crate) fn is_enum_variant_uninhabited_from<'db>(
    infcx: &InferCtxt<'db>,
    variant: EnumVariantId,
    subst: GenericArgs<'db>,
    target_mod: ModuleId,
    env: ParamEnv<'db>,
) -> bool

Checks whether a variant is visibly uninhabited from a particular module.