Delete relations that become empty

Fixes #465
Fixes #1454

js/id/actions/delete_node.js

@@ -15,7 +15,12 @@ iD.actions.DeleteNode = function(nodeId) {
 
         graph.parentRelations(node)
             .forEach(function(parent) {
-                graph = graph.replace(parent.removeMembersWithID(nodeId));
+                parent = parent.removeMembersWithID(nodeId);
+                graph = graph.replace(parent);
+
+                if (parent.isDegenerate()) {
+                    graph = iD.actions.DeleteRelation(parent.id)(graph);
+                }
             });
 
         return graph.remove(node);

js/id/actions/delete_relation.js

@@ -11,7 +11,12 @@ iD.actions.DeleteRelation = function(relationId) {
 
         graph.parentRelations(relation)
             .forEach(function(parent) {
-                graph = graph.replace(parent.removeMembersWithID(relationId));
+                parent = parent.removeMembersWithID(relationId);
+                graph = graph.replace(parent);
+
+                if (parent.isDegenerate()) {
+                    graph = iD.actions.DeleteRelation(parent.id)(graph);
+                }
             });
 
         _.uniq(_.pluck(relation.members, 'id')).forEach(function(memberId) {

js/id/actions/delete_way.js

@@ -11,7 +11,12 @@ iD.actions.DeleteWay = function(wayId) {
 
         graph.parentRelations(way)
             .forEach(function(parent) {
-                graph = graph.replace(parent.removeMembersWithID(wayId));
+                parent = parent.removeMembersWithID(wayId);
+                graph = graph.replace(parent);
+
+                if (parent.isDegenerate()) {
+                    graph = iD.actions.DeleteRelation(parent.id)(graph);
+                }
             });
 
         _.uniq(way.nodes).forEach(function(nodeId) {

js/id/core/relation.js

@@ -31,6 +31,10 @@ _.extend(iD.Relation.prototype, {
         });
     },
 
+    isDegenerate: function() {
+        return this.members.length === 0;
+    },
+
     // Return an array of members, each extended with an 'index' property whose value
     // is the member index.
     indexedMembers: function() {

test/spec/actions/delete_node.js

@@ -42,4 +42,12 @@ describe("iD.actions.DeleteNode", function () {
             graph  = action(iD.Graph([node1, node2, way]));
         expect(graph.hasEntity(way.id)).to.be.undefined;
     });
+
+    it("deletes parent relations that become empty", function () {
+        var node1    = iD.Node(),
+            relation = iD.Relation({members: [{ id: node1.id }]}),
+            action   = iD.actions.DeleteNode(node1.id),
+            graph    = action(iD.Graph([node1, relation]));
+        expect(graph.hasEntity(relation.id)).to.be.undefined;
+    });
 });

test/spec/actions/delete_relation.js

@@ -74,6 +74,14 @@ describe("iD.actions.DeleteRelation", function () {
         expect(graph.hasEntity(node.id)).to.be.undefined;
     });
 
+    it("deletes parent relations that become empty", function () {
+        var child  = iD.Relation(),
+            parent = iD.Relation({members: [{ id: child.id }]}),
+            action = iD.actions.DeleteRelation(child.id),
+            graph  = action(iD.Graph([child, parent]));
+        expect(graph.hasEntity(parent.id)).to.be.undefined;
+    });
+
     describe("#disabled", function() {
         it("returns 'incomplete_relation' if the relation is incomplete", function() {
             var relation = iD.Relation({members: [{id: 'w'}]}),

test/spec/actions/delete_way.js

@@ -8,7 +8,7 @@ describe("iD.actions.DeleteWay", function() {
 
     it("removes a way from parent relations", function() {
         var way      = iD.Way(),
-            relation = iD.Relation({members: [{ id: way.id }]}),
+            relation = iD.Relation({members: [{ id: way.id }, { id: 'w-2' }]}),
             action   = iD.actions.DeleteWay(way.id),
             graph    = iD.Graph([way, relation]).update(action);
         expect(_.pluck(graph.entity(relation.id).members, 'id')).not.to.contain(way.id);
@@ -60,4 +60,12 @@ describe("iD.actions.DeleteWay", function() {
             graph  = iD.Graph([node, way]).update(action);
         expect(graph.hasEntity(node.id)).not.to.be.undefined;
     });
+
+    it("deletes parent relations that become empty", function () {
+        var way      = iD.Way(),
+            relation = iD.Relation({members: [{ id: way.id }]}),
+            action   = iD.actions.DeleteWay(way.id),
+            graph    = iD.Graph([way, relation]).update(action);
+        expect(graph.hasEntity(relation.id)).to.be.undefined;
+    });
 });

test/spec/core/relation.js

@@ -56,6 +56,16 @@ describe('iD.Relation', function () {
         });
     });
 
+    describe("#isDegenerate", function () {
+        it("returns true for a relation without members", function () {
+            expect(iD.Relation().isDegenerate()).to.equal(true);
+        });
+
+        it("returns false for a relation with members", function () {
+            expect(iD.Relation({members: [{id: 'a', role: 'inner'}]}).isDegenerate()).to.equal(false);
+        });
+    });
+
     describe("#memberByRole", function () {
         it("returns the first member with the given role", function () {
             var r = iD.Relation({members: [