How to code a custom plugin to create DSL elements similar to "dependencies {}" or "repositories {}"

Old Forum Archive
1

How can I code my custom plugin to support scripts like this:

apply plugin: ‘thingsPlugin’

configurations {

config1 }

things {

config1 name:“Thing 1”, version:“3.3”, weight:“10 pounds”

config1 name:“Another thing”

config2 name:“Something else”, colour:“black” }

Obviously a contrived example, but the intention is to create a new DSL block (“things”) that associates information with native Gradle configurations in a manner similar to the “dependencies” or “repositories” blocks do.

I made a small bit of progress by defining a method in my build script that delegates to a custom “handler” that I created in a manner similar of DefaultDependenciesHandler:

void things( Closure configureClosure ) {

ThingsHandler thingsHandler = new DefaultThingsHandler(configurations)

ConfigureUtil.configure(configureClosure, thingsHandler); }

That seemed to work (aside from me needing to move the thingsHandler instantiation out of the method). But I don’t know how to get my plugin to define the new “things” method at the project scope. This question could have been posed as “How do you code a plugin to add a method to the Project?”. Thanks for any pointers…/rob

2

I think the way to do this is using gradle’s extension stuff, chapter 51.3 of the userguide: http://www.gradle.org/docs/current/userguide/custom_plugins.html

In your extension object, you can (for example) implement methodMissing to handle the configuration closure.

3

Thanks for the pointer. I got something working by creating an extension object from a custom “configuration” class (though I don’t know if that terminology is still current in gradle-1.0). My convention class contained a field for a “handler” object that implemented methodMissing as you suggested. I patterned it from the DefaultDependencyHandler in the gradle source. So I ended up with something like this:

class MyPlugin implements Plugin<Project>
 {
    void apply(Project project) {
        project.configure(project) {
            extensions.create("mystuff", MyConvention, project)
        }
    }
}
  class MyConvention {
    DefaultThingHandler things
      def MyConvention(Project project) {
        this.things = new DefaultThingHandler(project)
    }
      void things(Closure configureClosure) {
        ConfigureUtil.configure(configureClosure, this.things)
    }
}
  class DefaultThingHandler {..} // patterned off of Gradle's internal DefaultDependencyHandler

So although I dont have a first class “things” object at the same level as “repositories” or “dependencies”, I get the next best thing:

configurations {
    myconfig
}
  myStuff {
    things {
        myconfig name:'whatever', colour:'black', price:'59.95'
    }
}

Thanks for the help.

4

The ‘MyConvention’ stuff was only necessary before extensions came along. Instead, simply do ‘project.extensions.things = new DefaultThingHandler(project)’, and use it like this;

things {
  // configure DefaultThingHandler in here
}

‘DefaultThingHandler’ doesn’t need any special methods to make this work. Also see the “Writing Plugins” chapter in the Gradle user guide.

5

Instead of:

project.extensions.things = new DefaultThingHandler(project)

You should do:

project.extensions.create(“things”, DefaultThingHandler, project)

This adds some extra behaviour to the eventual extension (this will become more important in the future).

For example, this makes the extension extensible.

project.extensions.create(“things”, DefaultThingHandler, project)

project.things.extensions.create(“nestedThings”, DefaultThingHandler, project)

6

Can these be made to mean the same? I prefer the former syntax, and it isn’t obvious that it isn’t as “good”.

7

I tried this in the plugin’s apply() method:

extensions.create("things", DefaultThingHandler, project)

to support this in my build script:

things {
    myconfig name:'whatever', colour:'black', price:'59.95'
}

but it didn’t work because “things” was not found to be a method taking a Closure argument:

> Could not find method things() for arguments [sample_4p96i3djuvadhncfl6iatdnskb$_run_closure5@1408325] on root project 'myPlugin'.

I tried this before and assumed it could not be done, which is why I went back to creating my “convention” class containing a field for the DefaultThingHandler object.

8

Can you post your complete plugin please.