Bug 423715 - ArtifactComparatorFactory reports available comparators

Method getArtifactComparator(String) should report which artifact
comparators are available. When troubleshooting, user of standalone
applications and Ant tasks will have more information.

Change-Id: Iba7ea48c139c5ae365bc898804b38dc7cd75cc55
Signed-off-by: Mykola Nikishov <mn@mn.com.ua>

2 files changed, 6 insertions, 3 deletions

diff --git a/bundles/org.eclipse.equinox.p2.artifact.repository/src/org/eclipse/equinox/internal/p2/artifact/repository/messages.properties b/bundles/org.eclipse.equinox.p2.artifact.repository/src/org/eclipse/equinox/internal/p2/artifact/repository/messages.properties
index 33689fcb8..ada52de67 100644
--- a/bundles/org.eclipse.equinox.p2.artifact.repository/src/org/eclipse/equinox/internal/p2/artifact/repository/messages.properties
+++ b/bundles/org.eclipse.equinox.p2.artifact.repository/src/org/eclipse/equinox/internal/p2/artifact/repository/messages.properties
@@ -40,7 +40,7 @@ mirror_alreadyExists=Artifact: {0} already exists in repository: {1}.
 message_artifactsFromChildRepos=Messages while reading artifacts from child repositories
 message_problemReadingArtifact=Problems while reading artifacts from {0}
 
-exception_comparatorNotFound = The Artifact Comparator {0} was not found.
+exception_comparatorNotFound = The Artifact Comparator {0} was not found. Available artifact comparators: {1}.
 exception_noComparators = No Artifact Comparators are available.
 MirrorLog_Console_Log=Logging to the console instead.
 MirrorLog_Exception_Occurred=An exception occurred while writing to the log:
diff --git a/bundles/org.eclipse.equinox.p2.repository.tools/src/org/eclipse/equinox/p2/repository/tools/comparator/ArtifactComparatorFactory.java b/bundles/org.eclipse.equinox.p2.repository.tools/src/org/eclipse/equinox/p2/repository/tools/comparator/ArtifactComparatorFactory.java
index 49bdf7302..b8a6dcbff 100644
--- a/bundles/org.eclipse.equinox.p2.repository.tools/src/org/eclipse/equinox/p2/repository/tools/comparator/ArtifactComparatorFactory.java
+++ b/bundles/org.eclipse.equinox.p2.repository.tools/src/org/eclipse/equinox/p2/repository/tools/comparator/ArtifactComparatorFactory.java
@@ -13,6 +13,7 @@
 package org.eclipse.equinox.p2.repository.tools.comparator;
 
 import java.util.*;
+import java.util.stream.Collectors;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.RegistryFactory;
 import org.eclipse.equinox.internal.p2.artifact.repository.Messages;
@@ -40,8 +41,10 @@ public class ArtifactComparatorFactory {
 		if (artifactComparator.isPresent())
 			return artifactComparator.get();
 
-		if (comparatorID != null)
-			throw new IllegalArgumentException(NLS.bind(Messages.exception_comparatorNotFound, comparatorID));
+		if (comparatorID != null) {
+			String comparators = extensions.stream().map(extension -> extension.getAttribute(ATTR_ID)).collect(Collectors.joining(", ")); //$NON-NLS-1$
+			throw new IllegalArgumentException(NLS.bind(Messages.exception_comparatorNotFound, comparatorID, comparators));
+		}
 		throw new IllegalArgumentException(Messages.exception_noComparators);
 	}