option.fork = true was necessary to set options in java compiler for early versions of gradle but shouldn’t be necessary in gradle 2 as that answer by Peter Niederwieser suggested (1).
Stills gradle documentation specify some options such as bootClasspath need option.fork = true to work (2).
Why?
(I’ve successfully set options.bootClasspath in gradle 2.2.1 on several desks without option.fork = true)
(1): http://stackoverflow.com/questions/12554829/passing-arguments-to-compiler-and-javadoc-in-gradle
(2): https://docs.gradle.org/current/dsl/org.gradle.api.tasks.compile.CompileOptions.html#org.gradle.api.tasks.compile.CompileOptions:bootClasspath