in src/main/java/org/apache/maven/resolver/internal/ant/types/Dependencies.java [51:73]
public void validate(Task task) {
if (isReference()) {
getRef().validate(task);
} else {
if (getPom() != null && getPom().getFile() == null) {
throw new BuildException("A <pom> used for dependency resolution has to be backed by a pom.xml file");
}
Map<String, String> ids = new HashMap<>();
for (DependencyContainer container : containers) {
container.validate(task);
if (container instanceof Dependency) {
Dependency dependency = (Dependency) container;
String id = dependency.getVersionlessKey();
String collision = ids.put(id, dependency.getVersion());
if (collision != null) {
throw new BuildException("You must not declare multiple <dependency> elements"
+ " with the same coordinates but got " + id + " -> " + collision + " vs "
+ dependency.getVersion());
}
}
}
}
}