Add debug tool for positioning phase

lib/debug.js

@@ -53,3 +53,39 @@ exports.dotOrdering = function(g) {
 
   return result;
 };
+
+/**
+ * Renders a graph in a stringified DOT format that indicates the position of
+ * of all of the nodes in the graph. This is best used with neato - dot does
+ * not appear to respect position information.
+ */
+exports.dotPositioning = function(g) {
+  var result = 'digraph {',
+      scale = 0.1; // scale factor for graphviz
+
+  g.eachNode(function(u, attrs) {
+    if (!g.children(u).length) {
+      result += u + ' [pos="' + (attrs.x * scale) + ',' + (-attrs.y * scale) + '!"';
+      if (attrs.dummy) {
+        result += ', shape=diamond';
+      } else if (attrs.rightBorderSegment) {
+        result += ', shape=larrow';
+      } else if (attrs.leftBorderSegment) {
+        result += ', shape=rarrow';
+      } else if (attrs.nestingGraphTop) {
+        result += ', shape=invtriangle';
+      } else if (attrs.nestingGraphBottom) {
+        result += ', shape=triangle';
+      }
+      result += ', label="' + u + ' ' + attrs.x + ',' + attrs.y + '"];';
+    }
+  });
+
+  g.eachEdge(function(e, u, v) {
+    result += u + '->' + v + ';';
+  });
+
+  result += '}';
+
+  return result;
+};