Bug 512457 - Report errors before they get eaten up by runInBatchMode

Save the exception from inside runBatched and not have runInBatchMode return failure, so we can then expose the exception.

services/sync/modules/engines/bookmarks.js

@@ -93,11 +93,7 @@ BookmarksEngine.prototype = {
   _storeObj: BookmarksStore,
   _trackerObj: BookmarksTracker,
 
-  _sync: function BookmarksEngine__sync() {
-    Svc.Bookmark.runInBatchMode({
-      runBatched: Utils.bind2(this, SyncEngine.prototype._sync)
-    }, null);
-  }
+  _sync: Utils.batchSync("Bookmark", SyncEngine)
 };
 
 function BookmarksStore() {

services/sync/modules/engines/history.js

@@ -81,11 +81,7 @@ HistoryEngine.prototype = {
   _storeObj: HistoryStore,
   _trackerObj: HistoryTracker,
 
-  _sync: function HistoryEngine__sync() {
-    Svc.History.runInBatchMode({
-      runBatched: Utils.bind2(this, SyncEngine.prototype._sync)
-    }, null);
-  },
+  _sync: Utils.batchSync("History", SyncEngine),
 
   // History reconciliation is simpler than the default one from SyncEngine,
   // because we have the advantage that we can use the URI as a definitive

services/sync/modules/util.js

@@ -124,6 +124,29 @@ let Utils = {
     };
   },
 
+  batchSync: function batchSync(service, engineType) {
+    return function batchedSync() {
+      let engine = this;
+      let batchEx = null;
+
+      // Try running sync in batch mode
+      Svc[service].runInBatchMode({
+        runBatched: function wrappedSync() {
+          try {
+            engineType.prototype._sync.call(engine);
+          }
+          catch(ex) {
+            batchEx = ex;
+          }
+        }
+      }, null);
+
+      // Expose the exception if something inside the batch failed
+      if (batchEx!= null)
+        throw batchEx;
+    };
+  },
+
   // Generates a brand-new globally unique identifier (GUID).
   makeGUID: function makeGUID() {
     let uuidgen = Cc["@mozilla.org/uuid-generator;1"].

services/sync/tests/unit/test_bookmark_batch_fail.js

@@ -0,0 +1,19 @@
+_("Making sure a failing sync reports a useful error");
+Cu.import("resource://weave/engines/bookmarks.js");
+
+function run_test() {
+  let engine = new BookmarksEngine();
+  engine._syncStartup = function() {
+    throw "FAIL!";
+  };
+
+  try {
+    _("Try calling the sync that should throw right away");
+    engine._sync();
+    do_throw("Should have failed sync!");
+  }
+  catch(ex) {
+    _("Making sure what we threw ended up as the exception:", ex);
+    do_check_eq(ex, "FAIL!");
+  }
+}