Fetch downstream issue to compare labels on sync

src/main/java/org/hibernate/infra/replicate/jira/JiraConfig.java

@@ -92,6 +92,24 @@ interface JiraProjectGroup {
 		 * for the timeframe to end and will get process
 		 */
 		EventProcessing processing();
+
+		/**
+		 * Allows customizing formatting options.
+		 */
+		Formatting formatting();
+	}
+
+	interface Formatting {
+
+		/**
+		 * Specify how the label is formatted for a downstream issue.
+		 * <p>
+		 * Template receives a single String token that is an upstream label. {@code %s}
+		 * <b>must</b> be used in the template as it will be replaced by a {@code .+}
+		 * regex to find matches in the already synced labels.
+		 */
+		@WithDefault("upstream-%s")
+		String labelTemplate();
 	}
 
 	interface EventProcessing {

src/main/java/org/hibernate/infra/replicate/jira/service/jira/HandlerProjectContext.java

@@ -4,6 +4,7 @@
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.regex.Pattern;
 
 import org.hibernate.infra.replicate.jira.JiraConfig;
 import org.hibernate.infra.replicate.jira.service.jira.client.JiraRestClient;
@@ -37,6 +38,7 @@ public final class HandlerProjectContext implements AutoCloseable {
 	private final JiraUser notMappedAssignee;
 
 	private final Map<String, HandlerProjectContext> allProjectsContextMap;
+	private final Pattern sourceLabelPattern;
 
 	public HandlerProjectContext(String projectName, String projectGroupName, JiraRestClient sourceJiraClient,
 			JiraRestClient destinationJiraClient, HandlerProjectGroupContext projectGroupContext,
@@ -55,6 +57,8 @@ public HandlerProjectContext(String projectName, String projectGroupName, JiraRe
 				.map(v -> new JiraUser(projectGroup().users().mappedPropertyName(), v)).orElse(null);
 
 		this.allProjectsContextMap = allProjectsContextMap;
+		this.sourceLabelPattern = Pattern
+				.compile(projectGroupContext.projectGroup().formatting().labelTemplate().formatted(".+"));
 	}
 
 	public JiraConfig.JiraProject project() {
@@ -217,4 +221,8 @@ public Optional<HandlerProjectContext> contextForProjectInSameGroup(String proje
 		}
 		return Optional.ofNullable(allProjectsContextMap.get(project));
 	}
+
+	public boolean isSourceLabel(String label) {
+		return sourceLabelPattern.matcher(label).matches();
+	}
 }

src/main/java/org/hibernate/infra/replicate/jira/service/jira/handler/JiraIssueAbstractEventHandler.java

@@ -5,6 +5,7 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.regex.Pattern;
 
 import org.hibernate.infra.replicate.jira.JiraConfig;
 import org.hibernate.infra.replicate.jira.service.jira.HandlerProjectContext;
@@ -20,6 +21,8 @@
 
 abstract class JiraIssueAbstractEventHandler extends JiraEventHandler {
 
+	private static final Pattern FIX_VERSION_PATTERN = Pattern.compile("Fix_version:.++");
+
 	public JiraIssueAbstractEventHandler(ReportingConfig reportingConfig, HandlerProjectContext context, Long id) {
 		super(reportingConfig, context, id);
 	}
@@ -30,7 +33,8 @@ protected void applyTransition(JiraIssue sourceIssue, String destinationKey) {
 	}
 
 	protected void updateIssueBody(JiraIssue sourceIssue, String destinationKey) {
-		JiraIssue issue = issueToCreate(sourceIssue);
+		JiraIssue destIssue = context.destinationJiraClient().getIssue(destinationKey);
+		JiraIssue issue = issueToCreate(sourceIssue, destIssue);
 
 		updateIssue(destinationKey, issue, sourceIssue, context.notMappedAssignee());
 	}
@@ -83,7 +87,7 @@ protected JiraRemoteLink remoteSelfLink(JiraIssue sourceIssue) {
 		return link;
 	}
 
-	protected JiraIssue issueToCreate(JiraIssue sourceIssue) {
+	protected JiraIssue issueToCreate(JiraIssue sourceIssue, JiraIssue downstreamIssue) {
 		JiraIssue destinationIssue = new JiraIssue();
 		destinationIssue.fields = new JiraFields();
 
@@ -93,17 +97,7 @@ protected JiraIssue issueToCreate(JiraIssue sourceIssue) {
 				Objects.toString(sourceIssue.fields.description, ""));
 		destinationIssue.fields.description = truncateContent(destinationIssue.fields.description);
 
-		destinationIssue.fields.labels = sourceIssue.fields.labels;
-		// let's also add fix versions to the labels
-		if (sourceIssue.fields.fixVersions != null) {
-			if (destinationIssue.fields.labels == null) {
-				destinationIssue.fields.labels = List.of();
-			}
-			destinationIssue.fields.labels = new ArrayList<>(destinationIssue.fields.labels);
-			for (JiraSimpleObject fixVersion : sourceIssue.fields.fixVersions) {
-				destinationIssue.fields.labels.add("Fix version:%s".formatted(fixVersion.name).replace(' ', '_'));
-			}
-		}
+		destinationIssue.fields.labels = prepareLabels(sourceIssue, downstreamIssue);
 
 		// if we can map the priority - great we'll do that, if no: we'll keep it blank
 		// and let Jira use its default instead:
@@ -155,6 +149,38 @@ protected JiraIssue issueToCreate(JiraIssue sourceIssue) {
 		return destinationIssue;
 	}
 
+	private List<String> prepareLabels(JiraIssue sourceIssue, JiraIssue downstreamIssue) {
+		List<String> labelsToSet = new ArrayList<>();
+
+		for (String label : sourceIssue.fields.labels) {
+			labelsToSet.add(asUpstreamLabel(label));
+		}
+
+		// let's also add fix versions to the labels
+		if (sourceIssue.fields.fixVersions != null) {
+			for (JiraSimpleObject fixVersion : sourceIssue.fields.fixVersions) {
+				String fixVersionLabel = "Fix version:%s".formatted(fixVersion.name).replace(' ', '_');
+				labelsToSet.add(fixVersionLabel);
+			}
+		}
+
+		for (String label : downstreamIssue.fields.labels) {
+			if (!(context.isSourceLabel(label) || isFixVersion(label))) {
+				labelsToSet.add(label);
+			}
+		}
+
+		return labelsToSet;
+	}
+
+	private boolean isFixVersion(String label) {
+		return FIX_VERSION_PATTERN.matcher(label).matches();
+	}
+
+	private String asUpstreamLabel(String label) {
+		return context.projectGroup().formatting().labelTemplate().formatted(label);
+	}
+
 	private JiraUser toUser(String value) {
 		return new JiraUser(context.projectGroup().users().mappedPropertyName(), value);
 	}