There is no ECVS_TOPDIR variable in cvs.eclass. Reproducible: Always Steps to Reproduce:
As stated in the devmanual: "f you have any corrections, suggestions or improvements please file a bug at bugs.gentoo.org and assign it to qa@gentoo.org." Reassigning.
Fixed in https://gitweb.gentoo.org/proj/devmanual.git/commit/?id=fbf6a52165e813f436490091402e3c901e2e716f