Instead of storing the mirror ids, the new getMirrors method is used.

p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/repository/DefaultRepositoryIdManager.java

@@ -18,6 +18,7 @@
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
 import org.codehaus.plexus.component.annotations.Component;
 import org.codehaus.plexus.component.annotations.Requirement;
@@ -40,11 +41,6 @@ public class DefaultRepositoryIdManager implements IRepositoryIdManager {
 
     private Map<URI, String> knownMavenRepositoryIds = new ConcurrentHashMap<>();
 
-	/**
-	 * Map of known mirror identifiers, indexed by their URI.
-	 */
-	private Map<URI, String> knownMavenMirrorIds = new ConcurrentHashMap<>();
-
     @Override
     public void addMapping(String mavenRepositoryId, URI location) {
         if (mavenRepositoryId == null)
@@ -57,15 +53,6 @@ public void addMapping(String mavenRepositoryId, URI location) {
             logger.warn("p2 repository with URL " + key + " is associated with multiple IDs; was '" + previousValue
                     + "', now is '" + mavenRepositoryId + "'");
         }
-
-		// Checks if a mirror exists for the given location
-        MavenRepositoryLocation repositoryLocation = new MavenRepositoryLocation(mavenRepositoryId, key);
-		MavenRepositoryLocation mirrorLocation = settings.getMirror(repositoryLocation);
-		if (mirrorLocation != null) {
-			// A mirror exists. Adds its id to the map of known mirror ids.
-			URI mirrorKey = normalize(mirrorLocation.getURL());
-			knownMavenMirrorIds.put(mirrorKey, mirrorLocation.getId());
-		}
     }
 
     private static URI normalize(URI location) {
@@ -132,9 +119,11 @@ private static boolean certainlyNoRemoteURL(URI location) {
 
     @Override
 	public Stream<MavenRepositoryLocation> getKnownMavenRepositoryLocations() {
-		return Stream.concat(knownMavenRepositoryIds.entrySet().stream(), knownMavenMirrorIds.entrySet().stream())
-				.map(e -> new MavenRepositoryLocation(e.getValue(), e.getKey()));
-    }
+		// Returns both repository and mirror locations
+		return Stream.concat(
+				knownMavenRepositoryIds.entrySet().stream().map(e -> new MavenRepositoryLocation(e.getValue(), e.getKey())),
+				StreamSupport.stream(settings.getMirrors().spliterator(), false));
+	}
 
 	@Override
 	public MavenRepositorySettings getSettings() {