// extensionArtifacts
            Set<Artifact> extensionArtifacts = new HashSet<>();
            List<Extension> extensions =
                    project.getModel().getDelegate().getBuild().getExtensions();
            if (extensions != null) {
                for (Extension ext : extensions) {
                    String version;
                    if (ext.getVersion() == null || ext.getVersion().isEmpty()) {

                            EMPTY,
                            problems,
                            errOn30,
                            Version.V20,
                            p.getExtensions(),
                            p.getKey(),
                            p);

                    validate20EffectivePluginDependencies(problems, p, request);
                }

    //
    // Implementation
    //

    private File findArtifact(MavenProject project, Artifact artifact) {
        // POMs are always returned from the file system
        if ("pom".equals(artifact.getExtension())) {
            return project.getFile();
        }

        // First check in the project local repository
        File packagedArtifactFile = findInProjectLocalRepository(artifact);

                            dependency.getGroupId(),
                            dependency.getArtifactId(),
                            dependency.getClassifier(),
                            dependency.getType().getExtension(),
                            dependency.getVersion().toString(),
                            null),
                    dependency.getScope().id());
        }
        if (!managed && "".equals(dep.getScope())) {

    }

    private String id(org.apache.maven.artifact.Artifact artifact) {
        return artifact.getGroupId()
                + ":" + artifact.getArtifactId()
                + ":" + artifact.getArtifactHandler().getExtension()
                + (artifact.getClassifier() == null || artifact.getClassifier().isEmpty()
                        ? ""
                        : ":" + artifact.getClassifier())

File, java.io.File) throws java.io.IOException; public static java.io.File toFile(java.net.URL); public static java.net.URL[] toURLs(java.io.File[]) throws java.io.IOException; public static String removeExtension(String); public static String getExtension(String); public static String removePath(String); public static String removePath(String, char); public static String getPath(String); public static String getPath(String, char); public static void copyFileToDirectory(String, String) throws java.io.IOException;...