improvement(snapshots): add preserve stop times flag to avoid normalizing stop_sequence

re conveyal/gtfs-lib#283

Author: landonreed

src/main/java/com/conveyal/datatools/editor/jobs/CreateSnapshotJob.java

@@ -87,7 +87,7 @@ public void jobLogic() {
         Collection<Snapshot> existingSnapshots = feedSource.retrieveSnapshots();
         int version = existingSnapshots.size();
         status.update("Creating snapshot...", 20);
-        FeedLoadResult loadResult = makeSnapshot(namespace, DataManager.GTFS_DATA_SOURCE);
+        FeedLoadResult loadResult = makeSnapshot(namespace, DataManager.GTFS_DATA_SOURCE, !feedSource.preserveStopTimes);
         snapshot.version = version;
         snapshot.namespace = loadResult.uniqueIdentifier;
         snapshot.feedLoadResult = loadResult;

src/main/java/com/conveyal/datatools/editor/jobs/ExportSnapshotToGTFSJob.java

@@ -52,6 +52,7 @@ public void jobLogic() {
         FeedLoadResult result = exporter.exportTables();
         if (result.fatalException != null) {
             status.fail(String.format("Error (%s) encountered while exporting database tables.", result.fatalException));
+            return;
         }
 
         // Override snapshot ID if exporting feed for use as new feed version.

src/main/java/com/conveyal/datatools/manager/models/FeedSource.java

@@ -47,9 +47,17 @@ public class FeedSource extends Model implements Cloneable {
     /**
      * The collection of which this feed is a part
      */
-    //@JsonView(JsonViews.DataDump.class)
     public String projectId;
 
+    /**
+     * When snapshotting a GTFS feed for editing, gtfs-lib currently defaults to normalize stop sequence values to be
+     * zero-based and incrementing. This can muck with GTFS files that are linked to GTFS-rt feeds by stop_sequence, so
+     * this override flag currently provides a workaround for feeds that need to be edited but do not need to edit
+     * stop_times or individual patterns. WARNING: enabling this flag for a feed and then attempting to edit patterns in
+     * complicated ways (e.g., modifying the order of pattern stops) could have unexpected consequences.
+     */
+    public boolean preserveStopTimes;
+
     /**
      * Get the Project of which this feed is a part
      */