prevent creation of ways with duplicate segments or repeated nodes

js/id/behavior/drag_node.js

@@ -103,13 +103,26 @@ iD.behavior.DragNode = function(context) {
         if (cancelled) return;
         off();
 
+        function adjacent(d) {
+            return _.any(context.graph().parentWays(entity).map(function(w) {
+                return w.areAdjacent(d.id, entity.id);
+            }));
+        }
+
         var d = datum();
+
         if (d.type === 'way') {
             var choice = iD.geo.chooseIndex(d, d3.mouse(context.surface().node()), context);
             context.replace(
                 iD.actions.MoveNode(entity.id, choice.loc),
                 iD.actions.AddVertex(d.id, entity.id, choice.index),
                 connectAnnotation(d));
+
+        } else if (d.type === 'node' && adjacent(d)) {
+            context.replace(
+                    iD.actions.DeleteNode(entity.id),
+                    t('operations.delete.annotation.vertex'));
+
         } else if (d.type === 'node' && d.id !== entity.id) {
             context.replace(
                 iD.actions.Connect([entity.id, d.id]),

js/id/behavior/draw_way.js

@@ -139,6 +139,10 @@ iD.behavior.DrawWay = function(context, wayId, index, mode, baseGraph) {
 
     // Connect the way to an existing node and continue drawing.
     drawWay.addNode = function(node) {
+
+        // Avoid creating duplicate segments
+        if (way.areAdjacent(node.id, way.nodes[way.nodes.length - 1])) return;
+
         context.perform(
             ReplaceTemporaryNode(node),
             annotation);

js/id/core/way.js

@@ -57,6 +57,16 @@ _.extend(iD.Way.prototype, {
         return _.uniq(this.nodes).length < (this.isArea() ? 3 : 2);
     },
 
+    areAdjacent: function(n1, n2) {
+        for (var i = 0; i < this.nodes.length; i++) {
+            if (this.nodes[i]  === n1) {
+                if (this.nodes[i - 1] === n2) return true;
+                if (this.nodes[i + 1] === n2) return true;
+            }
+        }
+        return false;
+    },
+
     geometry: function() {
         return this.isArea() ? 'area' : 'line';
     },