Fixes #4842 by also writing deprecated pods to the proto.

Summary: Added a test case which shows the round trip works.

Test Plan:
#1 sbt test
#2 start marathon with --internal_store_backend legacy_zk, create pods, restart marathon and get pods and the root group.

Reviewers: unterstein, jasongilanfarr

Reviewed By: unterstein, jasongilanfarr

Subscribers: jenkins, marathon-team

Differential Revision: https://phabricator.mesosphere.com/D342

src/main/scala/mesosphere/marathon/state/Group.scala

@@ -30,6 +30,7 @@ class Group(
       .setId(id.toString)
       .setVersion(version.toString)
       .addAllDeprecatedApps(apps.map { case (_, app) => app.toProto })
+      .addAllDeprecatedPods(pods.map { case (_, pod) => pod.toProto })
       .addAllGroups(groupsById.map { case (_, group) => group.toProto })
       .addAllDependencies(dependencies.map(_.toString))
       .build()

src/main/scala/mesosphere/marathon/state/RootGroup.scala

@@ -6,9 +6,7 @@ import com.wix.accord.dsl._
 import mesosphere.marathon.Protos.GroupDefinition
 import mesosphere.marathon.api.v2.Validation._
 import mesosphere.marathon.core.externalvolume.ExternalVolumes
-import mesosphere.marathon.state.PathId._
 import mesosphere.marathon.core.pod.PodDefinition
-import mesosphere.marathon.stream._
 
 import org.jgrapht.DirectedGraph
 import org.jgrapht.alg.CycleDetector
@@ -426,22 +424,7 @@ object RootGroup {
 
   def empty: RootGroup = RootGroup(version = Timestamp(0))
 
-  def fromProto(msg: GroupDefinition): RootGroup = {
-    require(msg.getId.toPath.isRoot, "`RootGroup.fromProto` requires that the `id` be root.")
-    RootGroup(
-      apps = msg.getDeprecatedAppsList.map { proto =>
-        val app = AppDefinition.fromProto(proto)
-        app.id -> app
-      }(collection.breakOut),
-      pods = msg.getDeprecatedPodsList.map { proto =>
-        val pod = PodDefinition.fromProto(proto)
-        pod.id -> pod
-      }(collection.breakOut),
-      groupsById = msg.getGroupsList.map(fromProto).map(group => group.id -> group)(collection.breakOut),
-      dependencies = msg.getDependenciesList.map(PathId.apply)(collection.breakOut),
-      version = Timestamp(msg.getVersion)
-    )
-  }
+  def fromProto(msg: GroupDefinition): RootGroup = RootGroup.fromGroup(Group.fromProto(msg))
 
   def fromGroup(group: Group): RootGroup = {
     require(group.id.isRoot)

src/test/scala/mesosphere/marathon/state/RootGroupTest.scala

@@ -486,5 +486,33 @@ class RootGroupTest extends FunSpec with GivenWhenThen with Matchers with GroupC
       Then("validation is successful")
       validResult.isSuccess should be(true)
     }
+
+    it("can be written to proto and read back again") {
+      Given("A group with subgroups, apps and pods")
+      val app = AppDefinition(PathId("/app"))
+      val pod = PodDefinition(PathId("/pod"))
+      val subGroup = Group(PathId("/group"), transitiveAppsById = Map.empty, transitivePodsById = Map.empty)
+      val group = Group(
+        id = PathId.empty,
+        apps = Map(app.id -> app),
+        pods = Map(pod.id -> pod),
+        groupsById = Map(subGroup.id -> subGroup),
+        transitiveAppsById = Map(app.id -> app),
+        transitivePodsById = Map(pod.id -> pod)
+      )
+      val rootGroup = RootGroup(
+        apps = Map(app.id -> app),
+        pods = Map(pod.id -> pod),
+        groupsById = Map(subGroup.id -> subGroup)
+      )
+
+      When("Round trip toProto -> fromProto")
+      val protoGroup = Group.fromProto(group.toProto)
+      val protoRootGroup = RootGroup.fromProto(rootGroup.toProto)
+
+      Then("The round trip is successful")
+      protoGroup should be(group)
+      protoRootGroup should be(rootGroup)
+    }
   }
 }