gradle: how to write a groovy task - gradle

Question

I've been trying to work through the user guide. This seems like an incredibly simple thing I want to do, but I just can't figure out how to make it work.
I want to write an external groovy file to define a task, then call that task in build.gradle. Here's my build.gradle file:
// Apply the groovy plugin to add support for Groovy
apply plugin: 'groovy'
// In this section you declare where to find the dependencies of your project
repositories {
// Use 'jcenter' for resolving your dependencies.
// You can declare any Maven/Ivy/file repository here.
jcenter()
}
// In this section you declare the dependencies for your production and test code
dependencies {
// We use the latest groovy 2.x version for building this library
compile 'org.codehaus.groovy:groovy-all:2.4.7'
compile gradleApi()
compile localGroovy()
// We use the awesome Spock testing and specification framework
testCompile 'org.spockframework:spock-core:1.0-groovy-2.4'
testCompile 'junit:junit:4.12'
}
task myTask (type: my.package.MyTask)
Then, under src/main/groovy/my/package I have MyTask.groovy:
package my.package
import org.gradle.api.DefaultTask
import org.gradle.api.tasks.TaskAction
class MyTask extends DefaultTask {
String greeting = 'hello from MyTask'
#TaskAction
def greet(){
println greeting
}
}
I can't even list the tasks:
$ gradle tasks
FAILURE: Build failed with an exception.
* Where:
Build file '/projects/gradle/build.gradle' line: 21
* What went wrong:
A problem occurred evaluating root project 'gradle'.
> Could not get unknown property 'my' for root project 'gradle' of type org.gradle.api.Project.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
BUILD FAILED
Total time: 3.193 secs
At this point, I have absolutely no idea what's going on or how to do what I want. This seems like the most simple possible example but following the user guide has gotten me nowhere. No matter what I do, I can't get past that exception.
How do I write a groovy file and use that to define a new task in the build file?

Answer 1

You have to place your groovy files under:
rootProjectDir/buildSrc/src/main/groovy
Reference:
https://docs.gradle.org/current/userguide/custom_tasks.html#N14573
EDIT
I never tried changing the location of buildSrc but it appears to be an unresolved issue:
https://issues.gradle.org/browse/GRADLE-2816
(correct it if I'm wrong)

Answer 2

Now that you've got your src moved to buildSrc you'll also need to fix a small typo in MyTask.groovy:
Instead of
import org.gradle.api.tasks.DefaultTask
use
import org.gradle.api.tasks.TaskAction
That ought to fix your #TaskAction annotation.