  We address the electron transport characteristics in bulk half-Heusler alloys
with their compositions tuned to the borderline between topologically
nontrivial semi-metallic and trivial semiconducting phases. The precise
first-principles calculations based on the coherent potential approximation
(CPA) reveal that all the studied systems exhibit sets of dispersionless
impurity-like resonant levels, with one of them being located right at the
Dirac point. By means of the Kubo formalism we reveal that the residual
conductivity of these alloys is strongly suppressed by impurity scattering,
whereas the spin Hall conductivity exhibits a large value which is comparable
to that of Pt, thereby leading to divergent spin Hall angles.
