Appendix B. Potential Traps

B.1. Groovy script variables

For Gradle users it is important to understand how Groovy deals with script variables. Groovy has two types of script variables. One with a local scope and one with a script-wide scope.

Example B.1. Variables scope: local and script wide

scope.groovy

String localScope1 = 'localScope1'
def localScope2 = 'localScope2'
scriptScope = 'scriptScope'

println localScope1
println localScope2
println scriptScope

closure = {
    println localScope1
    println localScope2
    println scriptScope
}

def method() {
    try {
        localScope1
    } catch (MissingPropertyException e) {
        println 'localScope1NotAvailable'
    }
    try {
        localScope2
    } catch(MissingPropertyException e) {
        println 'localScope2NotAvailable'
    }
    println scriptScope
}

closure.call()
method()

Output of gradle

> gradle 
localScope1
localScope2
scriptScope
localScope1
localScope2
scriptScope
localScope1NotAvailable
localScope2NotAvailable
scriptScope

Variables which are declared with a type modifier are visible within closures but not visible within methods. This is a heavily discussed behavior in the Groovy community. ^[27]

B.2. Configuration and execution phase

It is important to keep in mind that Gradle has a distinct configuration and execution phase (see Chapter 56, The Build Lifecycle).

Example B.2. Distinct configuration and execution phase

build.gradle

def classesDir = file('build/classes')
classesDir.mkdirs()
task clean(type: Delete) {
    delete 'build'
}
task compile(dependsOn: 'clean') << {
    if (!classesDir.isDirectory()) {
        println 'The class directory does not exist. I can not operate'
        // do something
    }
    // do something
}

Output of gradle -q compile

> gradle -q compile
The class directory does not exist. I can not operate

As the creation of the directory happens during the configuration phase, the clean task removes the directory during the execution phase.

^[27]One of those discussions can be found here: http://groovy.329449.n5.nabble.com/script-scoping-question-td355887.html