SubmoduleOp: sort subscriptions before creating gitlink commit message

This commit makes sure that the commit message for the
super repo is created with an sorted list of subscriptions.

Without this fix, the following test could fail because the
commit message may change for different runs.

SubmoduleSubscriptionsWholeTopicMergeIT#updateManySubmodules

Change-Id: If84195c04fb89b1397295d0d80b6b697f20598e4

java/com/google/gerrit/server/git/SubmoduleOp.java

@@ -14,6 +14,8 @@
 
 package com.google.gerrit.server.git;
 
+import static java.util.Comparator.comparing;
+
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.MultimapBuilder;
 import com.google.common.collect.SetMultimap;
@@ -47,6 +49,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
@@ -416,7 +419,10 @@ public class SubmoduleOp {
     DirCache dc = readTree(or.rw, currentCommit);
     DirCacheEditor ed = dc.editor();
     int count = 0;
-    for (SubmoduleSubscription s : targets.get(subscriber)) {
+
+    List<SubmoduleSubscription> subscriptions = new ArrayList<>(targets.get(subscriber));
+    Collections.sort(subscriptions, comparing((SubmoduleSubscription s) -> s.getPath()));
+    for (SubmoduleSubscription s : subscriptions) {
       if (count > 0) {
         msgbuf.append("\n\n");
       }

javatests/com/google/gerrit/acceptance/git/SubmoduleSubscriptionsWholeTopicMergeIT.java

@@ -346,17 +346,17 @@ public class SubmoduleSubscriptionsWholeTopicMergeIT extends AbstractSubmoduleSu
           "master",
           "Update git submodules\n\n"
               + "* Update "
-              + name("sub3")
+              + name("sub1")
               + " from branch 'master'\n  to "
-              + sub3HEAD
+              + sub1HEAD
               + "\n\n* Update "
               + name("sub2")
               + " from branch 'master'\n  to "
               + sub2HEAD
               + "\n\n* Update "
-              + name("sub1")
+              + name("sub3")
               + " from branch 'master'\n  to "
-              + sub1HEAD);
+              + sub3HEAD);
     }
 
     superRepo