feat: allow to create child elements from the context pad

The intention of the pad is to make create simpler, there is no need
to carry "should not be child element" restrictions around.

Closes #2391

Author: nikku

lib/features/rules/BpmnRules.js

@@ -271,10 +271,6 @@ function nonExistingOrLabel(element) {
   return !element || isLabel(element);
 }
 
-function isSame(a, b) {
-  return a === b;
-}
-
 /**
  * @param {Element} element
  *
@@ -967,16 +963,6 @@ function canCreate(shape, target, source, position) {
     return true;
   }
 
-  if (isSame(source, target)) {
-    return false;
-  }
-
-  // ensure we do not drop the element
-  // into source
-  if (source && isParent(source, target)) {
-    return false;
-  }
-
   return canDrop(shape, target, position) || canInsert(shape, target, position);
 }
 

test/spec/features/context-pad/ContextPadProviderSpec.js

@@ -482,6 +482,48 @@ describe('features - context-pad', function() {
       })
     );
 
+
+    describe('drop onto sub-process', function() {
+
+      var basicTests = [
+        { action: 'append.append-task', expectedElement: 'bpmn:Task' },
+        { action: 'append.intermediate-event', expectedElement: 'bpmn:IntermediateThrowEvent', iit: it.only }
+      ];
+
+
+      for (const { action, expectedElement, iit = it } of basicTests) {
+
+        iit(`should create ${expectedElement}`, inject(function(dragging, contextPad, elementRegistry) {
+
+          // given
+          var subProcess = elementRegistry.get('SubProcess_1');
+
+          // when
+          contextPad.open(subProcess);
+
+          contextPad.trigger('dragstart', padEvent(action));
+
+          dragging.move(canvasEvent({ x: subProcess.x, y: subProcess.y }));
+          dragging.hover({ element: subProcess });
+          dragging.move(canvasEvent({ x: subProcess.x + 200, y: subProcess.y + 70 }));
+          dragging.end();
+
+          // then
+          // find new, unnamed element
+          var newElement = subProcess.children.find(element => {
+            return (
+              is(element, expectedElement) &&
+              !element.businessObject.name
+            );
+          });
+
+          expect(newElement, `element of type ${expectedElement}`).to.exist;
+        }));
+
+      }
+
+    });
+
   });