I’m having a compatibility issue. In Gradle 2.7, the following works fine:
configurations { provided }
sourceSets.main.compileClasspath += [configurations.provided]
In 2.8-rc-1, I get
Cannot cast object '[configuration ':provided']' with class 'java.util.ArrayList' to class 'org.gradle.api.file.FileCollection' due to: groovy.lang.GroovyRuntimeException: Could not find matching constructor for: org.gradle.api.file.FileCollection(org.gradle.api.internal.artifacts.configurations.DefaultConfiguration_Decorated)
Removing the brackets and adding just the single configuration makes it work, but an earlier Gradle version required the brackets.