--- Revision None
+++ Revision 363161623439
@@ -0,0 +1,26 @@
+// failures maps failed save attempts to the error that caused them (validation, conflict, etc.)
+function(doc, req, failures) {
+  var newDoc = doc || {_id: req.query.id || "example"};
+
+  if(!(newDoc._id in failures)) {
+    // Legacy code does this now. It knows nothing about the failures argument, but
+    // just blindly attempts a save. Possibilities:
+    // 1. Successful save. Normal code path.
+    // 2. Conflict or invalid. Erlang has 2 choices.
+    //    A. newDoc._id is not in failures; call me again with newDoc._id
+    //       added to the failures object.
+    //    B. newDoc._id is in failures. Erlang knows my code is naive or does
+    //       not know the new API; Same 409 Conflict as before.
+    return [newDoc, "Attempting a smart save: " + newDoc._id + "\n"];
+  } else {
+    var reason;
+    if('validation' in failures[newDoc._id]) {
+      reason = "Validation failure: " + JSON.stringify(failures[newDoc._id].validation);
+    } else if ('conflict' in failures[newDoc._id]) {
+      reason = "Document update conflict";
+    } else {
+      reason = 'Unknown reason';
+    }
+    return [null, "Sorry, this is not possible: " + reason + "\n"];
+  }
+}