*
     * @return a stream containing this node and its descendant
     */
    @Nonnull
    default Stream<Node> stream() {
        return Stream.concat(Stream.of(this), getChildren().stream().flatMap(Node::stream));
    }

                boolean recursive) {
            List<Callable<InterimResult>> tasks = pomFiles.stream()
                    .map(pomFile -> ((Callable<InterimResult>)
                            () -> build(projectIndex, pomFile, concat(aggregatorFiles, pomFile), root, recursive)))
                    .collect(Collectors.toList());
            try {
                List<Future<InterimResult>> futures = executor.invokeAll(tasks);

  <artifactId>maven-parent</artifactId>
  <version>5</version>
  <packaging>pom</packaging>
  <name>Apache Maven</name>
  <description>
    Maven is a software project management and comprehension tool. Based on the concept of a project object model
    (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.
  </description>
  <url>http://maven.apache.org/</url>
  <issueManagement>

            implements ExtensibleEnumRegistry<T> {

        private final Map<String, T> values;

        DefaultExtensibleEnumRegistry(List<P> providers, T... builtinValues) {
            values = Stream.<T>concat(
                            Stream.of(builtinValues), providers.stream().flatMap(p -> p.provides().stream()))
                    .collect(Collectors.toMap(t -> t.id(), t -> t));
        }

        @Override

     * Retrieve a stream of the project's artifacts
     */
    private Stream<Artifact> getProjectArtifacts(MavenProject project) {
        Stream<org.apache.maven.artifact.Artifact> artifacts = Stream.concat(
                Stream.concat(
                        // pom artifact
                        Stream.of(new ProjectArtifact(project)),
                        // main project artifact if not a pom

  <artifactId>maven</artifactId>
  <version>3.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>Apache Maven</name>
  <description>Maven is a project development management and
    comprehension tool. Based on the concept of a project object model:
    builds, dependency management, documentation creation, site
    publication, and distribution publication are all controlled from
    the declarative file. Maven can be extended by plugins to utilise a

  <artifactId>maven</artifactId>
  <version>3.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>Apache Maven</name>
  <description>Maven is a project development management and
    comprehension tool. Based on the concept of a project object model:
    builds, dependency management, documentation creation, site
    publication, and distribution publication are all controlled from
    the declarative file. Maven can be extended by plugins to utilise a

import org.codehaus.plexus.util.xml.Xpp3Dom;
import org.eclipse.aether.graph.DependencyFilter;
import org.eclipse.aether.repository.RemoteRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * The concern of the project is provide runtime values based on the model.
 * <p>
 * The values in the model remain untouched but during the process of building a project notions like inheritance and

        }
        return getModelId() + " " + getLocation();
    }

    public static InputSource merge(InputSource src1, InputSource src2) {
        return new InputSource(Stream.concat(src1.sources(), src2.sources()).collect(Collectors.toSet()));
    }

     * Do not include the POM artifact as the file can't be set anyway.
     */
    private Stream<org.apache.maven.artifact.Artifact> getProjectArtifacts(MavenProject project) {
        return Stream.concat(Stream.of(project.getArtifact()), project.getAttachedArtifacts().stream());
    }

    private String id(org.apache.maven.artifact.Artifact artifact) {
        return artifact.getGroupId()