How to write extension method for Gradle dependencies {} block

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I'm trying to write extension methods for DependencyHandler. One of main goals to have autocompletion of these methods.

So I wrote extension function in buildSrc project like this (Shortcuts.kt):

fun DependencyHandler.autoValue() {
    add("compileOnly", Libs.Auto.autoValueAnnotations)
    add("annotationProcessor", Libs.Auto.autoValueCompiler)
}

And registered it as extension module as described here:

# File: src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule
moduleName = buildSrc
moduleVersion = 1.0
extensionClasses = com.example.test.ShortcutsKt

I want to use these methods in build.gradle files like:

dependencies {
    ...
    autoValue()
}

It appears in autocompletion list inside dependencies{} block, but at configuration time I got error:

org.gradle.internal.metaobject.AbstractDynamicObject$CustomMessageMissingMethodException: Could not find method autoValue() for arguments [] on object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.
    at org.gradle.internal.metaobject.AbstractDynamicObject.methodMissingException(AbstractDynamicObject.java:179)
    at org.gradle.internal.metaobject.ConfigureDelegate.invokeMethod(ConfigureDelegate.java:87)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:430)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:369)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
    at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:158)
    at build_dh4v5lw1dkt4b2nii5ope5rmy$_run_closure1.doCall(/.../app/build.gradle:29)
kotlin build.gradle gradle groovy
1 Answers

Gradle DefaultDependencyHandler implements custom method resolution strategy (to handle scopes notation like testCompile(smth)), so additional methods can be added via dependencies.ext property:

dependencies.ext.autoValue = {
    dependencies.add("compileOnly", Libs.Auto.autoValueAnnotations)
    dependencies.add("annotationProcessor", Libs.Auto.autoValueCompiler)
}

But in this case you don't get autocompletion.

To enable autocompletion you can mix this two approaches and proxy extension methods from buildSrc via dependencies.ext:

import com.example.test.ShortcutsKt

import java.lang.reflect.Method
import java.lang.reflect.Modifier

// DependencyHandler implementation resolves all undeclared methods by self,
// so we need to add these extension methods to dependencies.ext
def methodNames = ShortcutsKt.declaredMethods
        .findAll { isDependencyHandlerExtension(it) }
        .collect { it.name }
        .unique()

methodNames.each { String methodName ->
    dependencies.ext[methodName] = { Object... args ->
        ShortcutsKt."$methodName"(dependencies, *args)
    }
}

private static boolean isDependencyHandlerExtension(Method method) {
    return Modifier.isPublic(method.getModifiers()) &&
            Modifier.isStatic(method.getModifiers()) &&
            method.parameterCount > 0 &&
            method.parameterTypes[0] == DependencyHandler.class
}
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