/**
* Creates both normal and scheduling middlemen.
*
* <p>Note: there's no need to synchronize this method; the only use of a field is via a call to
* another synchronized method (getArtifact()).
*
* @return null iff {@code inputs} is null or empty; the middleman file and the middleman action
* otherwise
*/
private Pair<Artifact, Action> createMiddleman(
ActionOwner owner,
String middlemanName,
String purpose,
Iterable<Artifact> inputs,
Root middlemanDir,
MiddlemanType middlemanType) {
if (inputs == null || Iterables.isEmpty(inputs)) {
return null;
}
Artifact stampFile = getStampFileArtifact(middlemanName, purpose, middlemanDir);
Action action = new MiddlemanAction(owner, inputs, stampFile, purpose, middlemanType);
actionRegistry.registerAction(action);
return Pair.of(stampFile, action);
}