it looks like Address would be perfectly happy if the target lived above its source root... for example: Address ==

.pants.d/gen/antlr:examples.src.antlr.org.pantsbuild.example.exp.exp_antlr3

, and source_root/target_base ==

.pants.d/gen/antlr/examples.src.antlr.org.pantsbuild.example.exp.exp_antlr3/6f5ca2b8caba/