Fix system tags conflict situations

Does not disrupt the UX whenever a tag or association was created
concurrently. The input field will adjust itself as if the tag was
already there in the first place.

core/js/systemtags/systemtagsinputfield.js

@@ -186,6 +186,12 @@
 			return false;
 		},
 
+		_addToSelect2Selection: function(selection) {
+			var data = this.$tagsField.select2('data');
+			data.push(selection);
+			this.$tagsField.select2('data', data);
+		},
+
 		/**
 		 * Event handler whenever a tag is selected.
 		 * Also called whenever tag creation is requested through the dummy tag object.
@@ -204,10 +210,27 @@
 					userAssignable: true
 				}, {
 					success: function(model) {
-						var data = self.$tagsField.select2('data');
-						data.push(model.toJSON());
-						self.$tagsField.select2('data', data);
+						self._addToSelect2Selection(model.toJSON());
 						self.trigger('select', model);
+					},
+					error: function(model, xhr) {
+						if (xhr.status === 409) {
+							// re-fetch collection to get the missing tag
+							self.collection.reset();
+							self.collection.fetch({
+								success: function(collection) {
+									// find the tag in the collection
+									var model = collection.where({name: e.object.name, userVisible: true, userAssignable: true});
+									if (model.length) {
+										model = model[0];
+										// the tag already exists or was already assigned,
+										// add it to the list anyway
+										self._addToSelect2Selection(model.toJSON());
+										self.trigger('select', model);
+									}
+								}
+							});
+						}
 					}
 				});
 				this.$tagsField.select2('close');

core/js/tests/specs/systemtags/systemtagsinputfieldSpec.js

@@ -158,6 +158,65 @@ describe('OC.SystemTags.SystemTagsInputField tests', function() {
 				expect(selectHandler.calledOnce).toEqual(true);
 				expect(selectHandler.getCall(0).args[0]).toEqual('2');
 			});
+			it('triggers select event and still adds to list even in case of conflict', function() {
+				var selectHandler = sinon.stub();
+				view.on('select', selectHandler);
+				var fetchStub = sinon.stub(OC.SystemTags.SystemTagsCollection.prototype, 'fetch');
+				var createStub = sinon.stub(OC.SystemTags.SystemTagsCollection.prototype, 'create');
+				view.$el.find('input').trigger(new $.Event('select2-selecting', {
+					object: {
+						id: -1,
+						name: 'newname',
+						isNew: true
+					}
+				}));
+
+				expect(createStub.calledOnce).toEqual(true);
+				expect(createStub.getCall(0).args[0]).toEqual({
+					name: 'newname',
+					userVisible: true,
+					userAssignable: true
+				});
+
+				var newModel = new OC.SystemTags.SystemTagModel({
+					id: '123',
+					name: 'newname',
+					userVisible: true,
+					userAssignable: true
+				});
+
+				// not called yet
+				expect(selectHandler.notCalled).toEqual(true);
+
+				select2Stub.withArgs('data').returns([{
+					id: '1',
+					name: 'abc'
+				}]);
+
+				// simulate conflict response for tag creation
+				createStub.yieldTo('error', view.collection, {status: 409});
+
+				// at this point it fetches from the server
+				expect(fetchStub.calledOnce).toEqual(true);
+				// simulate fetch result by adding model to the collection
+				view.collection.add(newModel);
+				fetchStub.yieldTo('success', view.collection);
+
+				expect(select2Stub.lastCall.args[0]).toEqual('data');
+				expect(select2Stub.lastCall.args[1]).toEqual([{
+						id: '1',
+						name: 'abc'
+					},
+					newModel.toJSON()
+				]);
+
+				// select event still called
+				expect(selectHandler.calledOnce).toEqual(true);
+				expect(selectHandler.getCall(0).args[0]).toEqual(newModel);
+
+				createStub.restore();
+				fetchStub.restore();
+			});
 		});
 		describe('tag actions', function() {
 			var opts;