*         have been attached yet
     * @throws IllegalArgumentException if the project is null
     * @see #getAllArtifacts(Project)
     */
    @Nonnull
    Collection<ProducedArtifact> getAttachedArtifacts(@Nonnull Project project);

    /**
     * Returns project's all artifacts as an immutable ordered collection. The collection contains:
     * <ul>
     *   <li>The project's artifacts ({@link Project#getArtifacts()}):

     */
    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()
                + ":" + artifact.getArtifactId()

                        "pom".equals(project.getPackaging()) ? Stream.empty() : Stream.of(project.getArtifact())),
                // attached artifacts
                project.getAttachedArtifacts().stream());
        return artifacts.map(RepositoryUtils::toArtifact);
    }

    private boolean isRegularFile(Artifact artifact) {
        return artifact.getFile() != null && artifact.getFile().isFile();