gradle use variables in parent task that are defined in child

Question

I have a multiproject gradle build where I declare a task in the parent build that uses a variable that gets declared in the child projects (the value can change depending on the subproject). However, I get an error during the configuration phase that the variable doesn't exist. My setup looks like

build.gradle (top level)

subprojects {
   myTask {
     prop = valueDefinedInChild
   }

}

And then

build.gradle (subproject)

valueDefinedInChild = 'someValue'

Is there a way to do this correctly?

Answer 1

There is a way to do this (project.evaluationDependsOnChildren()), but I recommend to only use it as a last resort. Instead, I'd configure the commonalities at the top level, and the differences at the subproject level:

build.gradle (top level):

subprojects {
    task myTask { // add task to all subprojects
        // common configuration goes here
    }
}

build.gradle (subproject):

myTask {
    prop = 'someValue'
}

Another way to avoid repeating yourself is to factor out common code into a separate script, and have subprojects include it with apply from:. This is a good choice when the logic only applies to selected subprojects, or in cases where it's desirable to avoid coupling between parent project and subprojects (e.g. when using Gradle's new configuration on demand feature).