Remove dependency on server generated type root folders

This change prepares the client to deal with implicit permanent folders
in Sync server updates. That includes the following:
- Expect type root folders to not come from the server on the initial
  sync. The client auto-creates type root folders for all types except
  Bookmarks and Nigori when progress marker changes from empty to
  non-empty. These folders are created as local nodes (with client IDs)
  that aren't expected to sync back to the server.
- Expect empty parent IDs in updates for both new and existing items.
- Because the client code updates first, the client must expect server
  to override locally created type root folders. To enable that the
  directory update code that matches update entities to local entities
  was updated to look at server unique tags in addition to client
  unique tags. Later when the server stops generating folders we
  should be able to remove that code.
- Added some extra special cases in Directory::CheckTreeInvariants to
  deal with client side created type root folders.
- Added / modified a few tests to cover cases with implicit parent IDs
  in updates.

BUG=438313

Review URL: https://codereview.chromium.org/867793003

Cr-Commit-Position: refs/heads/master@{#313977}

sync/engine/directory_update_handler.cc

@@ -9,6 +9,7 @@
 #include "sync/engine/update_applicator.h"
 #include "sync/sessions/directory_type_debug_info_emitter.h"
 #include "sync/syncable/directory.h"
+#include "sync/syncable/model_neutral_mutable_entry.h"
 #include "sync/syncable/syncable_model_neutral_write_transaction.h"
 #include "sync/syncable/syncable_write_transaction.h"
 
@@ -65,16 +66,42 @@ SyncerError DirectoryUpdateHandler::ProcessGetUpdatesResponse(
     }
   }
 
+  // Auto-create permanent folder for the type if the progress marker
+  // changes from empty to non-empty.
+  if (!IsTypeWithServerGeneratedRoot(type_) &&
+      dir_->HasEmptyDownloadProgress(type_) &&
+      IsValidProgressMarker(progress_marker)) {
+    CreateTypeRoot(&trans);
+  }
+
   UpdateSyncEntities(&trans, applicable_updates, status);
 
   if (IsValidProgressMarker(progress_marker)) {
     ExpireEntriesIfNeeded(&trans, progress_marker);
     UpdateProgressMarker(progress_marker);
   }
+
   debug_info_emitter_->EmitUpdateCountersUpdate();
   return SYNCER_OK;
 }
 
+void DirectoryUpdateHandler::CreateTypeRoot(
+    syncable::ModelNeutralWriteTransaction* trans) {
+  syncable::ModelNeutralMutableEntry entry(
+      trans, syncable::CREATE_NEW_TYPE_ROOT, type_);
+  if (!entry.good()) {
+    // This will fail only if matching entry already exists, for example
+    // if the type gets disabled and its progress marker gets cleared,
+    // then the type gets re-enabled again.
+    DVLOG(1) << "Type root folder " << ModelTypeToRootTag(type_)
+             << " already exists.";
+    return;
+  }
+
+  entry.PutServerIsDir(true);
+  entry.PutUniqueServerTag(ModelTypeToRootTag(type_));
+}
+
 void DirectoryUpdateHandler::ApplyUpdates(sessions::StatusController* status) {
   if (!IsApplyUpdatesRequired()) {
     return;
@@ -205,6 +232,9 @@ void DirectoryUpdateHandler::UpdateSyncEntities(
 
 bool DirectoryUpdateHandler::IsValidProgressMarker(
     const sync_pb::DataTypeProgressMarker& progress_marker) const {
+  if (progress_marker.token().empty()) {
+    return false;
+  }
   int field_number = progress_marker.data_type_id();
   ModelType model_type = GetModelTypeFromSpecificsFieldNumber(field_number);
   if (!IsRealDataType(model_type) || type_ != model_type) {

sync/engine/directory_update_handler.h

@@ -91,6 +91,9 @@ class SYNC_EXPORT_PRIVATE DirectoryUpdateHandler : public UpdateHandler {
   // Skips all checks and goes straight to applying the updates.
   SyncerError ApplyUpdatesImpl(sessions::StatusController* status);
 
+  // Creates root node for the handled model type.
+  void CreateTypeRoot(syncable::ModelNeutralWriteTransaction* trans);
+
   syncable::Directory* dir_;
   ModelType type_;
   scoped_refptr<ModelSafeWorker> worker_;

sync/engine/directory_update_handler_unittest.cc

@@ -84,6 +84,12 @@ class DirectoryUpdateHandlerProcessUpdateTest : public ::testing::Test {
     return e.good() && !e.GetIsDel();
   }
 
+  bool TypeRootExists(ModelType model_type) {
+    syncable::ReadTransaction trans(FROM_HERE, dir());
+    syncable::Entry e(&trans, syncable::GET_TYPE_ROOT, model_type);
+    return e.good() && !e.GetIsDel();
+  }
+
  protected:
   // Used in the construction of DirectoryTypeDebugInfoEmitters.
   ObserverList<TypeDebugInfoObserver> type_observers_;
@@ -267,27 +273,17 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, GarbageCollectionByVersion) {
   context.set_context("context");
   context.set_version(1);
 
-  scoped_ptr<sync_pb::SyncEntity> type_root =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("root")),
-                   Id::GetRoot().GetServerId(), SYNCED_NOTIFICATIONS);
-  type_root->set_server_defined_unique_tag(
-      ModelTypeToRootTag(SYNCED_NOTIFICATIONS));
-  type_root->set_folder(true);
-
   scoped_ptr<sync_pb::SyncEntity> e1 =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e1")),
-                   type_root->id_string(),
+      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e1")), "",
                    SYNCED_NOTIFICATIONS);
 
   scoped_ptr<sync_pb::SyncEntity> e2 =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e2")),
-                   type_root->id_string(),
+      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e2")), "",
                    SYNCED_NOTIFICATIONS);
   e2->set_version(kDefaultVersion + 100);
 
   // Add to the applicable updates list.
   SyncEntityList updates;
-  updates.push_back(type_root.get());
   updates.push_back(e1.get());
   updates.push_back(e2.get());
 
@@ -298,7 +294,7 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, GarbageCollectionByVersion) {
   handler.ApplyUpdates(&status);
 
   // Verify none is deleted because they are unapplied during GC.
-  EXPECT_TRUE(EntryExists(type_root->id_string()));
+  EXPECT_TRUE(TypeRootExists(SYNCED_NOTIFICATIONS));
   EXPECT_TRUE(EntryExists(e1->id_string()));
   EXPECT_TRUE(EntryExists(e2->id_string()));
 
@@ -308,7 +304,6 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, GarbageCollectionByVersion) {
             handler.ProcessGetUpdatesResponse(
                 progress, context, SyncEntityList(), &status));
   handler.ApplyUpdates(&status);
-  EXPECT_TRUE(EntryExists(type_root->id_string()));
   EXPECT_FALSE(EntryExists(e1->id_string()));
   EXPECT_TRUE(EntryExists(e2->id_string()));
 }
@@ -330,19 +325,11 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, ContextVersion) {
   old_context.set_context("data");
   old_context.set_data_type_id(field_number);
 
-  scoped_ptr<sync_pb::SyncEntity> type_root =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("root")),
-                   Id::GetRoot().GetServerId(), SYNCED_NOTIFICATIONS);
-  type_root->set_server_defined_unique_tag(
-      ModelTypeToRootTag(SYNCED_NOTIFICATIONS));
-  type_root->set_folder(true);
   scoped_ptr<sync_pb::SyncEntity> e1 =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e1")),
-                   type_root->id_string(),
+      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e1")), "",
                    SYNCED_NOTIFICATIONS);
 
   SyncEntityList updates;
-  updates.push_back(type_root.get());
   updates.push_back(e1.get());
 
   // The first response should be processed fine.
@@ -351,7 +338,9 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, ContextVersion) {
                 progress, old_context, updates, &status));
   handler.ApplyUpdates(&status);
 
-  EXPECT_TRUE(EntryExists(type_root->id_string()));
+  // The PREFERENCES root should be auto-created.
+  EXPECT_TRUE(TypeRootExists(SYNCED_NOTIFICATIONS));
+
   EXPECT_TRUE(EntryExists(e1->id_string()));
 
   {
@@ -368,8 +357,7 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest, ContextVersion) {
   new_context.set_data_type_id(field_number);
 
   scoped_ptr<sync_pb::SyncEntity> e2 =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e2")),
-                   type_root->id_string(),
+      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e2")), "",
                    SYNCED_NOTIFICATIONS);
   updates.clear();
   updates.push_back(e2.get());
@@ -410,21 +398,12 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest,
   context.set_context("context");
   context.set_version(1);
 
-  scoped_ptr<sync_pb::SyncEntity> type_root =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("root")),
-                   Id::GetRoot().GetServerId(), ARTICLES);
-  type_root->set_server_defined_unique_tag(ModelTypeToRootTag(ARTICLES));
-  type_root->set_folder(true);
-
-  scoped_ptr<sync_pb::SyncEntity> e1 =
-      CreateUpdate(SyncableIdToProto(Id::CreateFromServerId("e1")),
-                   type_root->id_string(),
-                   ARTICLES);
+  scoped_ptr<sync_pb::SyncEntity> e1 = CreateUpdate(
+      SyncableIdToProto(Id::CreateFromServerId("e1")), "", ARTICLES);
   sync_pb::AttachmentIdProto* attachment_id = e1->add_attachment_id();
   *attachment_id = CreateAttachmentIdProto();
 
   SyncEntityList updates;
-  updates.push_back(type_root.get());
   updates.push_back(e1.get());
 
   // Process and apply updates.
@@ -433,7 +412,7 @@ TEST_F(DirectoryUpdateHandlerProcessUpdateTest,
       handler.ProcessGetUpdatesResponse(progress, context, updates, &status));
   handler.ApplyUpdates(&status);
 
-  ASSERT_TRUE(EntryExists(type_root->id_string()));
+  ASSERT_TRUE(TypeRootExists(ARTICLES));
   ASSERT_TRUE(EntryExists(e1->id_string()));
   {
     syncable::ReadTransaction trans(FROM_HERE, dir());