Configuring a custom Gradle sourceSet using a closure

Question

I'm trying to develop a Gradle plugin for a language I use (SystemVerilog). I'm still experimenting and figuring things out. Before I write the entire thing as a plugin, I thought it would be best to try out the different parts I need inside a build script, to get a feel of how things should work.

I'm trying to define a container of source sets, similar to how the Java plugin does it. I'd like to be able to use a closure when configuring a source set. Concretely, I'd like to be able to do the following:

sourceSets {
    main {
        sv {
            include '*.sv'
        }
    }
}

I defined my own sourceSet class:

class SourceSet implements Named {
    final String name
    final ObjectFactory objectFactory

    @Inject
    SourceSet(String name, ObjectFactory objectFactory) {
        this.name = name
        this.objectFactory = objectFactory
    }

    SourceDirectorySet getSv() {
        SourceDirectorySet sv = objectFactory.sourceDirectorySet('sv',
            'SystemVerilog source')
        sv.srcDir("src/${name}/sv")
        return sv
    }

    SourceDirectorySet sv(@Nullable Closure configureClosure) {
        configure(configureClosure, getSv());
        return this;
    }
}

I'm using org.gradle.api.file.SourceDirectorySet because that already implements PatternFilterable, so it should give me access to include, exclude, etc.

If I understand the concept correctly, the sv(@Nullable Closure configureClosure) method is the one that gives me the ability to write sv { ... } to configure via a closure.

To add the sourceSets property to the project, I did the following:

project.extensions.add("sourceSets",
        project.objects.domainObjectContainer(SourceSet.class))

As per the Gradle docs, this should give me the possibility to configure sourceSets using a closure. This site, which details using custom types, states that by using NamedDomainObjectContainer, Gradle will provide a DSL that build scripts can use to define and configure elements. This would be the sourceSets { ... } part. This should also be the sourceSets { main { ... } } part.

If I create a sourceSet for main and use it in a task, then everything works fine:

project.sourceSets.create('main')

task compile(type: Task) {
    println 'Compiling source files'
    println project.sourceSets.main.sv.files
}

If I try to configure the main source set to only include files with the .sv extension, then I get an error:

sourceSets {
    main {
        sv {
            include '*.sv'
        }
    }
}

I get the following error:

No signature of method: build_47mnuak4y5k86udjcp7v5dkwm.sourceSets() is applicable for argument types: (build_47mnuak4y5k86udjcp7v5dkwm$_run_closure1) values: [build_47mnuak4y5k86udjcp7v5dkwm$_run_closure1@effb286]

I don't know what I'm doing wrong. I'm sure it's just a simple thing that I'm forgetting. Does anyone have an idea of what that might be?

Answer 1

I figured out what was going wrong. It was a combination of poor copy/paste skills and the fact that Groovy is a dynamic language.

First, let's look at the definition of the sv(Closure) function again:

SourceDirectorySet sv(@Nullable Closure configureClosure) {
    configure(configureClosure, getSv());
    return this;
}

Once I moved this code to an own Groovy file and used the IDE to show me what is getting called, I noticed that it wasn't calling the function I expected. I was expecting a call to org.gradle.util.ConfigureUtil.configure. Since this is part of the public API, I expected it to be imported by default in the build script. As this page states, this is not the case.

To solve the issue, it's enough to add the following import:

import static org.gradle.util.ConfigureUtil.configure

This will get rid of the cryptic closure related error. It is replaced by the following error, though:

Cannot cast object 'SourceSet_Decorated@a6abab9' with class 'SourceSet_Decorated' to class 'org.gradle.api.file.SourceDirectorySet'

This is caused by the copy/paste error I mentioned. When I wrote the SourceSet class, I drew heavily from org.gradle.api.tasks.SourceSet (and org.gradle.api.internal.tasks.DefaultSourceSet). If we look at the java(Closure) method there, we'll see it has the following signature:

SourceSet java(@Nullable Closure configureClosure);

Notice that it returns SourceSet and not SourceDirectorySet like in my code. Using the proper return type fixes the issue:

SourceSet sv(@Nullable Closure configureClosure)

With this new return type, let's look again at the configuration code for the source set:

sourceSets {
    main {
        sv {
            include '*.sv'
        }
    }
}

Initially, I thought it was supposed to work as follows: pass main { ... } as a Closure to sourceSets, pass sv { ... } as a Closure to main, and handle the include ... part inside sourceDirectorySet. I banged my head against the wall for a while, because I couldn't find any code in that class hierarchy that takes closures like this.

Now, I think the flow is slightly different: pass main { ... } as a Closure to sourceSets (as initially thought), but call the sv(Closure) function on main (of type sourceSet), passing it { include ... } as the argument.

---

Bonus: There was one more issue that wasn't related to the "compile" errors I was having.

Even after getting the code to run without errors, it still wasn't behaving as expected. I had some files with the *.svh extension that were still getting picked up. This is because, when calling getSv(), it was creating a new SourceDirectorySet each time. Any configuration that was done previously was getting thrown away each time that this function was called.

Making the sourceDirectorySet a class member and moving its creation to the constructor fixed the issue:

private SourceDirectorySet sv

SourceSet(String name, ObjectFactory objectFactory) {
    // ...
    sv = objectFactory.sourceDirectorySet('sv',
            'SystemVerilog source')
    sv.srcDir("src/${name}/sv")
}

SourceDirectorySet getSv() {
    return sv
}