in src/main/java/org/apache/maven/plugins/source/AbstractSourceJarMojo.java [323:329]
private boolean isAlreadyAttached(Artifact artifact, MavenProject checkProject, String classifier) {
return artifact.getType().equals(getType())
&& artifact.getGroupId().equals(checkProject.getGroupId())
&& artifact.getArtifactId().equals(checkProject.getArtifactId())
&& artifact.getVersion().equals(checkProject.getVersion())
&& (artifact.getClassifier() != null ? artifact.getClassifier().equals(classifier) : false);
}