fix(rules): do not allow message flows to outside diagram shapes

Closes #1033

lib/features/rules/BpmnRules.js

@@ -827,9 +827,17 @@ function canConnectAssociation(source, target) {
 
 function canConnectMessageFlow(source, target) {
 
-  return isMessageFlowSource(source) &&
-         isMessageFlowTarget(target) &&
-        !isSameOrganization(source, target);
+  // handle the case where target does not have a parent,
+  // because it is not dropped within the diagram (bpmn-io/bpmn-js#1033)
+  if (!target.parent) {
+    return false;
+  }
+
+  return (
+    isMessageFlowSource(source) &&
+    isMessageFlowTarget(target) &&
+    !isSameOrganization(source, target)
+  );
 }
 
 function canConnectSequenceFlow(source, target) {

test/spec/features/rules/BpmnRules.connectOnCreate.bpmn

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" id="sid-38422fae-e03e-43a3-bef4-bd33b32041b2" targetNamespace="http://bpmn.io/bpmn" exporter="bpmn-js (https://demo.bpmn.io)" exporterVersion="3.4.0">
+  <process id="Process_1" isExecutable="false">
+    <task id="Task_A" name="A" />
+  </process>
+  <bpmndi:BPMNDiagram id="BpmnDiagram_1">
+    <bpmndi:BPMNPlane id="BpmnPlane_1" bpmnElement="Process_1">
+      <bpmndi:BPMNShape id="Task_A_di" bpmnElement="Task_A">
+        <omgdc:Bounds x="156" y="81" width="100" height="80" />
+      </bpmndi:BPMNShape>
+    </bpmndi:BPMNPlane>
+  </bpmndi:BPMNDiagram>
+</definitions>

test/spec/features/rules/BpmnRulesSpec.js

@@ -1441,6 +1441,7 @@ describe('features/modeling/rules - BpmnRules', function() {
       }
     ));
 
+
     it('not attach IntermediateEvent to ReceiveTask after EventBasedGateway', inject(
       function(canvas, modeling, elementFactory, bpmnRules) {
 
@@ -1477,6 +1478,7 @@ describe('features/modeling/rules - BpmnRules', function() {
       }
     ));
 
+
     it('create IntermediateEvent in SubProcess body', inject(
       function(elementFactory, elementRegistry, bpmnRules) {
 
@@ -1791,6 +1793,41 @@ describe('features/modeling/rules - BpmnRules', function() {
   });
 
 
+  describe('connect on create', function() {
+
+    var testXML = require('./BpmnRules.connectOnCreate.bpmn');
+
+    beforeEach(bootstrapModeler(testXML, { modules: testModules }));
+
+
+    it('should handle target without parent', inject(function(elementFactory) {
+
+      // given
+      var types = [
+        'bpmn:Task',
+        'bpmn:StartEvent',
+        'bpmn:EndEvent',
+        'bpmn:Gateway'
+      ];
+
+      types.forEach(function(type) {
+        // when
+        var element = elementFactory.createShape({ type: type });
+
+        // then
+        expectCanConnect('Task_A', element, {
+          sequenceFlow: false,
+          messageFlow: false,
+          association: false,
+          dataAssociation: false
+        });
+      });
+
+    }));
+
+  });
+
+
   describe('data input / output', function() {
 
     describe('in process', function() {
@@ -1888,6 +1925,7 @@ describe('features/modeling/rules - BpmnRules', function() {
 
   });
 
+
   describe('start connection', function() {
 
     var testXML = require('../../../fixtures/bpmn/simple.bpmn');