Potential Traps

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: 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 groovy scope.groovy

> groovy scope.groovy
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.

Configuration and execution phase

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

Example 1. Distinct configuration and execution phase

GroovyKotlin

build.gradle

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

build.gradle.kts

val classesDir = file("build/classes")
classesDir.mkdirs()
tasks.register<Delete>("clean") {
    delete("build")
}
tasks.register("compile") {
    dependsOn("clean")
    doLast {
        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.