Improved stability of AQL Traverser. Also added checks for illegal edge cases

arangod/Aql/ExecutionPlan.cpp

@@ -648,6 +648,26 @@ ExecutionNode* ExecutionPlan::fromNodeTraversal (ExecutionNode* previous,
   AstNode const* start = node->getMember(1);
   AstNode const* graph = node->getMember(2);
 
+  if (start->type == NODE_TYPE_OBJECT &&
+      start->isConstant()) {
+    size_t n = start->numMembers();
+    for (size_t i = 0; i < n; ++i) {
+      auto member = start->getMember(i);
+      if (member->type == NODE_TYPE_OBJECT_ELEMENT &&
+          strncmp(member->getStringValue(), TRI_VOC_ATTRIBUTE_ID, member->getStringLength()) == 0) {  
+        start = member->getMember(0);
+        break;
+      }
+    }
+  }
+
+  if (start->type != NODE_TYPE_REFERENCE &&
+      start->type != NODE_TYPE_VALUE) {
+    // operand is some misc expression
+    auto calc = createTemporaryCalculation(start, previous);
+    start = _ast->createNodeReference(getOutVariable(calc));
+    previous = calc;
+  }
   // First create the node
   auto travNode = new TraversalNode(this, nextId(), _ast->query()->vocbase(),
           direction, start, graph);

arangod/Aql/TraversalBlock.cpp

@@ -115,7 +115,7 @@ TraversalBlock::TraversalBlock (ExecutionEngine* engine,
                                                                           _trx,
                                                                           _expressions));
   }
-  if (!ep->usesInVariable()) {
+  if (! ep->usesInVariable()) {
     _vertexId = ep->getStartVertex();
   }
   else {
@@ -365,12 +365,16 @@ void TraversalBlock::initializePaths (AqlItemBlock const* items) {
         }
       }
     }
-    else if (in._type == AqlValue::DOCVEC) {
-      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_QUERY_PARSE, 
-                                     std::string("Only one start vertex allowed. Embed it in a FOR loop."));
+    else if (in.isString()) {
+      _vertexId = in.toString();
+      VertexId v = triagens::arango::traverser::IdStringToVertexId (
+        _resolver,
+        _vertexId
+      );
+      _traverser->setStartVertex(v);
     }
     else {
-      TRI_ASSERT(in.getTypeString() == "");
+      _engine->getQuery()->registerWarning(TRI_ERROR_BAD_PARAMETER, "Invalid input for traversal: Only strings or objects with _id are allowed");
     }
   }
 }

arangod/VocBase/Traverser.h

@@ -269,7 +269,7 @@ namespace triagens {
           : _readDocuments(0),
             _filteredPaths(0),
             _pruneNext(false),
-            _done(false),
+            _done(true),
             _expressions(nullptr) {
           }
 
@@ -282,7 +282,7 @@ namespace triagens {
           : _readDocuments(0),
             _filteredPaths(0),
             _pruneNext(false),
-            _done(false),
+            _done(true),
             _opts(opts),
             _expressions(expressions) {
           }