feat(core): Add optional Error-Output (#7460)

Add an additional optional error output to which all items get sent that
could not be processed.
![Screenshot from 2023-10-18
17-29-15](https://github.com/n8n-io/n8n/assets/6249596/e9732807-ab2b-4662-a5f6-bdff24f7ad55)

Github issue / Community forum post (link here to close automatically):
https://community.n8n.io/t/error-connector-for-nodes/3094

https://community.n8n.io/t/error-handling-at-node-level-detect-node-execution-status/26791

---------

Co-authored-by: OlegIvaniv <me@olegivaniv.com>

packages/workflow/src/Interfaces.ts

@@ -920,6 +920,7 @@ export interface INodeCredentials {
 	[key: string]: INodeCredentialsDetails;
 }
 
+export type OnError = 'continueErrorOutput' | 'continueRegularOutput' | 'stopWorkflow';
 export interface INode {
 	id: string;
 	name: string;
@@ -934,6 +935,7 @@ export interface INode {
 	waitBetweenTries?: number;
 	alwaysOutputData?: boolean;
 	executeOnce?: boolean;
+	onError?: OnError;
 	continueOnFail?: boolean;
 	parameters: INodeParameters;
 	credentials?: INodeCredentials;
@@ -1546,6 +1548,7 @@ export interface INodeInputConfiguration {
 }
 
 export interface INodeOutputConfiguration {
+	category?: string;
 	displayName?: string;
 	required?: boolean;
 	type: ConnectionTypes;
@@ -1653,6 +1656,11 @@ export interface IWorkflowDataProxyData {
 	$thisItemIndex: number;
 	$now: any;
 	$today: any;
+	$getPairedItem: (
+		destinationNodeName: string,
+		incomingSourceData: ISourceData | null,
+		pairedItem: IPairedItemData,
+	) => INodeExecutionData | null;
 	constructor: any;
 }
 

packages/workflow/src/NodeHelpers.ts

@@ -1045,21 +1045,48 @@ export function getNodeOutputs(
 	node: INode,
 	nodeTypeData: INodeTypeDescription,
 ): Array<ConnectionTypes | INodeOutputConfiguration> {
+	let outputs: Array<ConnectionTypes | INodeOutputConfiguration> = [];
+
 	if (Array.isArray(nodeTypeData.outputs)) {
-		return nodeTypeData.outputs;
+		outputs = nodeTypeData.outputs;
+	} else {
+		// Calculate the outputs dynamically
+		try {
+			outputs = (workflow.expression.getSimpleParameterValue(
+				node,
+				nodeTypeData.outputs,
+				'internal',
+				{},
+			) || []) as ConnectionTypes[];
+		} catch (e) {
+			throw new Error(`Could not calculate outputs dynamically for node "${node.name}"`);
+		}
 	}
 
-	// Calculate the outputs dynamically
-	try {
-		return (workflow.expression.getSimpleParameterValue(
-			node,
-			nodeTypeData.outputs,
-			'internal',
-			{},
-		) || []) as ConnectionTypes[];
-	} catch (e) {
-		throw new Error(`Could not calculate outputs dynamically for node "${node.name}"`);
+	if (node.onError === 'continueErrorOutput') {
+		// Copy the data to make sure that we do not change the data of the
+		// node type and so change the displayNames for all nodes in the flow
+		outputs = deepCopy(outputs);
+		if (outputs.length === 1) {
+			// Set the displayName to "Success"
+			if (typeof outputs[0] === 'string') {
+				outputs[0] = {
+					type: outputs[0],
+				};
+			}
+			outputs[0].displayName = 'Success';
+		}
+		return [
+			...outputs,
+			{
+				category: 'error',
+				type: 'main',
+				displayName: 'Error',
+			},
+		];
 	}
+
+	return outputs;
 }
 
 /**

packages/workflow/src/RoutingNode.ts

@@ -121,8 +121,9 @@ export class RoutingNode {
 
 		// TODO: Think about how batching could be handled for REST APIs which support it
 		for (let i = 0; i < items.length; i++) {
+			let thisArgs: IExecuteSingleFunctions | undefined;
 			try {
-				const thisArgs = nodeExecuteFunctions.getExecuteSingleFunctions(
+				thisArgs = nodeExecuteFunctions.getExecuteSingleFunctions(
 					this.workflow,
 					this.runExecutionData,
 					runIndex,
@@ -209,7 +210,7 @@ export class RoutingNode {
 
 				returnData.push(...responseData);
 			} catch (error) {
-				if (get(this.node, 'continueOnFail', false)) {
+				if (thisArgs !== undefined && thisArgs.continueOnFail()) {
 					returnData.push({ json: {}, error: error.message });
 					continue;
 				}

packages/workflow/src/WorkflowDataProxy.ts

@@ -1211,6 +1211,7 @@ export class WorkflowDataProxy {
 			// eslint-disable-next-line @typescript-eslint/naming-convention
 			Duration,
 			...that.additionalKeys,
+			$getPairedItem: getPairedItem,
 
 			// deprecated
 			$jmespath: jmespathWrapper,