gradle task build already exists issue

Question

I am getting the error

Cannot add task ':webserver:build' as a task with that name already exists.

The weird thing is my hello task is fine but my build task is not AND YES, I am trying to override the Java plugin's build task.

Master build.gradle file:

allprojects {
   apply plugin: 'java'
   apply plugin: 'eclipse'

   task hello << { task -> println "I'm $task.project.name" }
   task build << { task -> println "I'm building now" }
}

subprojects {

    hello << {println "- I depend on stserver"}

    build << { println "source sets=$sourceSets.main.java.srcDirs" }
}

My child webserver build.gradle file:

sourceSets.main{
  java.srcDirs = ['app']
}

build << { println "source sets=$sourceSets.main.java.srcDirs" }

hello << {println "- Do something specific xxxx"}

What is the deal here, is overriding build special or something? Overriding my own hello task worked fine and I thought overriding build would be just as simple?

Answer 1

You aren't overriding the hello task, you are just adding more task actions. You can override a task with task foo(overwrite: true). I haven't come across a good reason to override the build task; there are probably better ways to achieve what you want.

Answer 2

What is the deal here, overriding build is special or something. Overriding my own hello task worked fine and I thought overriding build would be just as simple?

The reason the behaviour seems different is because build task already exists and hello does not (and not because build is special).

In gradle you cannot do this:

task hello << { print "hello" }
task hello << { print "hello again" }

This will fail with the familiar error: "Cannot add task ':hello' as a task with that name already exists.".

Since build task already exists, it's illegal to have a second task build << { ... }. However, it will work for hello task, because it does not exist, and therefore task hello << { ... } is legal, as it's the first declaration of hello task.

If you replace your task build << { ... } with build << { ... }, which just adds more behaviour to an existing task, it will "compile" fine.