eclipse.classpath.file.whenMerged requires the java plugin

[Yay295]

I needed to modify Eclipse's classpath, so I was trying to use

apply plugin: 'eclipse'
eclipse.classpath.file.whenMerged {
    println 'is not printed'
    ...
}

but nothing was happening. After trying a lot of different things I happened to move that code after a apply plugin: 'java' statement I had in my script, and it started working.

apply plugin: 'java'
apply plugin: 'eclipse'
eclipse.classpath.file.whenMerged {
    println 'is printed'
    ...
}

Is it intentional that this only works with the Java plugin applied, and is there anywhere that Buildship's special handling of eclipse.classpath.file is documented?

Related:
https://discuss.gradle.org/t/how-does-buildship-create-the-classpath-file-for-eclipse/26252
#923
possibly #1133