Fix PluginConfig.setGroupReference method

When the group reference was a new one, i.e. not already in the groups
file, it was not added to the groups file when saving the project
config.

Change-Id: If40bcc3fae8c1966bda21adc1b6d46d63b88e4ec

gerrit-server/src/main/java/com/google/gerrit/server/config/PluginConfig.java

@@ -159,6 +159,7 @@ public class PluginConfig {
   }
 
   public void setGroupReference(String name, GroupReference value) {
-    setString(name, value.toConfigValue());
+    GroupReference groupRef = projectConfig.resolve(value);
+    setString(name, groupRef.toConfigValue());
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/git/ProjectConfig.java

@@ -403,7 +403,13 @@ public class ProjectConfig extends VersionedMetaData implements ValidationError.
   }
 
   public GroupReference resolve(GroupReference group) {
-    return groupList.resolve(group);
+    GroupReference groupRef = groupList.resolve(group);
+    if (groupRef != null
+        && groupRef.getUUID() != null
+        && !groupsByName.containsKey(groupRef.getName())) {
+      groupsByName.put(groupRef.getName(), groupRef);
+    }
+    return groupRef;
   }
 
   /** @return the group reference, if the group is used by at least one rule. */

gerrit-server/src/test/java/com/google/gerrit/server/git/ProjectConfigTest.java

@@ -466,6 +466,14 @@ public class ProjectConfigTest extends LocalDiskRepositoryTestCase {
                 + "\tkey1 = "
                 + staff.toConfigValue()
                 + "\n");
+    assertThat(text(rev, "groups"))
+        .isEqualTo(
+            "# UUID\tGroup Name\n" //
+                + "#\n" //
+                + staff.getUUID().get()
+                + "     \t"
+                + staff.getName()
+                + "\n");
   }
 
   private ProjectConfig read(RevCommit rev) throws IOException, ConfigInvalidException {