StreamingMarkupBuilder.out evaluates 'it' as a namespace prefix

I'm trying to generate a pom from custom Artifact groovy class using the following code:

def outputBuilder = new StreamingMarkupBuilder()

    List<Artifact> artifacts = []
    artifacts << new Artifact(groupId: "g", artifactId: "a", version: "v")
    artifacts << new Artifact(groupId: "g1", artifactId: "a1", version: "v1")

    def pom = {
        project() {
            modelVersion("4.0.0")
            groupId("gi")
            artifactId("ai")
            version("007")
            packaging("pom")
            dependencyManagement() {
                out <<
                        artifacts.each {
                            dependency {
                                groupId(it.groupId)
                            }
                        }
            }
        }
    }

    println outputBuilder.bind(pom)
}

Running this simple example yields this error:

Exception in thread "main" groovy.lang.GroovyRuntimeException: Namespace prefix: groupId is not bound to a URI
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:77)
at org.codehaus.groovy.reflection.CachedConstructor.doConstructorInvoke(CachedConstructor.java:71)
at org.codehaus.groovy.runtime.callsite.ConstructorSite$ConstructorSiteNoUnwrap.callConstructor(ConstructorSite.java:81)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallConstructor(CallSiteArray.java:57)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:182)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:190)
at groovy.xml.StreamingMarkupBuilder$_closure6.doCall(StreamingMarkupBuilder.groovy:130)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:272)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.Closure.call(Closure.java:411)
at groovy.xml.streamingmarkupsupport.BaseMarkupBuilder$Document.invokeMethod(BaseMarkupBuilder.java:148)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:423)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:346)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:730)
at groovy.lang.GroovyObjectSupport.invokeMethod(GroovyObjectSupport.java:44)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:407)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:346)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:730)
at groovy.lang.GroovyObjectSupport.invokeMethod(GroovyObjectSupport.java:44)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:407)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:346)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:730)
at groovy.lang.GroovyObjectSupport.invokeMethod(GroovyObjectSupport.java:44)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:407)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:346)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:730)
at groovy.lang.GroovyObjectSupport.invokeMethod(GroovyObjectSupport.java:44)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:407)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:346)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:66)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:49)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:133)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:141)

Once I change groupId(it.groupId) to groupId("XXX") the pom is printed fine.

How can I "trick groovy" to evaluate the iterator variable groupId instead of evaluating it as a missing namespace prefix. groupId("$it.groupId") and such didn't work.

Solution

it is the implicit variable of the surrounding closure. In your case, it represents the implicit variable for closure dependency{} which is incorrect. You would mean it to be a variable representing each artifact from artifacts.

Solution, use like below:

....
artifacts.each{ar -> 
    dependency{
        groupId(ar.groupId)
    }
}
......