@Override
	public void merge(TaskMonitor monitor) {

		mergeManager.setInProgress(EXTERNAL_PROGRAM_PHASE);
		int transactionID = resultPgm.startTransaction(getDescription());
		boolean commit = false;
		try {
			monitor.checkCancelled();
			clearResolveInfo();

			autoMerge(monitor);

			monitor.checkCancelled();
			mergeConflicts(ASK_USER, monitor);
			monitor.checkCancelled();
			clearConflictPanel();
			showResolveInfo();
			commit = true;
		}
		catch (CancelledException e) {
			mergeManager.setStatusText("User cancelled merge.");
			cancel();
		}
		finally {
			resultPgm.endTransaction(transactionID, commit);
		}
		mergeManager.setCompleted(EXTERNAL_PROGRAM_PHASE);
	}
Returns an array of symbol ID groups for all the external programs that are in conflict.
Ghidra/Features/Base/src/main/java/ghidra/app/merge/listing/ExternalProgramMerger.java