Function rustc_trait_selection::traits::specialize::specializes

pub(super) fn specializes(
    tcx: TyCtxt<'_>, 
    (impl1_def_id, impl2_def_id): (DefId, DefId)
) -> bool

Is impl1 a specialization of impl2?

Specialization is determined by the sets of types to which the impls apply; impl1 specializes impl2 if it applies to a subset of the types impl2 applies to.