I was trying to merge jEdit programmer's editor and got errors on javamail that took a little while to track down, so here's how to fix it.
BUILD FAILED
Target "-push-to-maven-init" does not exist in the project "JavaMail". It is used from target "push-to-maven-prepare".
build.xml of dev-java/oracle-javamail-1.5.6 contains:
<!DOCTYPE project [
<!ENTITY commonBuild SYSTEM "ant-common.xml">
]>
...
&commonBuild;
And ant-common.xml contains necessary code.
BUT
Python xml.sax module by default does not expand external entities since Python 3.6.7, 3.7.1 and 3.8.0
SOLUTION:
There is a script
https://gitweb.gentoo.org/proj/javatoolkit.git/commit/?id=5480034ddf29a050671aa22effdd1cefb1a97f55