feat: Introduce prompt type option for Agent, Basic LLM Chain, and QA Chain nodes (#8697)

Signed-off-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Michael Kret <michael.k@radency.com>

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/ChainLlm.node.ts

@@ -22,7 +22,11 @@ import { LLMChain } from 'langchain/chains';
 import type { BaseChatModel } from 'langchain/chat_models/base';
 import { HumanMessage } from 'langchain/schema';
 import { getTemplateNoticeField } from '../../../utils/sharedFields';
-import { isChatInstance } from '../../../utils/helpers';
+import {
+	getOptionalOutputParsers,
+	getPromptInputByType,
+	isChatInstance,
+} from '../../../utils/helpers';
 
 interface MessagesTemplate {
 	type: string;
@@ -204,7 +208,7 @@ function getInputs(parameters: IDataObject) {
 		},
 	];
 
-	// If `hasOutputParser` is undefined it must be version 1.1 or earlier so we
+	// If `hasOutputParser` is undefined it must be version 1.3 or earlier so we
 	// always add the output parser input
 	if (hasOutputParser === undefined || hasOutputParser === true) {
 		inputs.push({ displayName: 'Output Parser', type: NodeConnectionType.AiOutputParser });
@@ -218,7 +222,7 @@ export class ChainLlm implements INodeType {
 		name: 'chainLlm',
 		icon: 'fa:link',
 		group: ['transform'],
-		version: [1, 1.1, 1.2, 1.3],
+		version: [1, 1.1, 1.2, 1.3, 1.4],
 		description: 'A simple chain to prompt a large language model',
 		defaults: {
 			name: 'Basic LLM Chain',
@@ -279,6 +283,59 @@ export class ChainLlm implements INodeType {
 					},
 				},
 			},
+			{
+				displayName: 'Prompt',
+				name: 'promptType',
+				type: 'options',
+				options: [
+					{
+						// eslint-disable-next-line n8n-nodes-base/node-param-display-name-miscased
+						name: 'Take from previous node automatically',
+						value: 'auto',
+						description: 'Looks for an input field called chatInput',
+					},
+					{
+						// eslint-disable-next-line n8n-nodes-base/node-param-display-name-miscased
+						name: 'Define below',
+						value: 'define',
+						description:
+							'Use an expression to reference data in previous nodes or enter static text',
+					},
+				],
+				displayOptions: {
+					hide: {
+						'@version': [1, 1.1, 1.2, 1.3],
+					},
+				},
+				default: 'auto',
+			},
+			{
+				displayName: 'Text',
+				name: 'text',
+				type: 'string',
+				required: true,
+				default: '',
+				placeholder: 'e.g. Hello, how can you help me?',
+				typeOptions: {
+					rows: 2,
+				},
+				displayOptions: {
+					show: {
+						promptType: ['define'],
+					},
+				},
+			},
+			{
+				displayName: 'Require Specific Output Format',
+				name: 'hasOutputParser',
+				type: 'boolean',
+				default: false,
+				displayOptions: {
+					hide: {
+						'@version': [1, 1.1, 1.3],
+					},
+				},
+			},
 			{
 				displayName: 'Chat Messages (if Using a Chat Model)',
 				name: 'messages',
@@ -419,17 +476,6 @@ export class ChainLlm implements INodeType {
 					},
 				],
 			},
-			{
-				displayName: 'Require Specific Output Format',
-				name: 'hasOutputParser',
-				type: 'boolean',
-				default: false,
-				displayOptions: {
-					show: {
-						'@version': [1.2],
-					},
-				},
-			},
 			{
 				displayName: `Connect an <a data-action='openSelectiveNodeCreator' data-action-parameter-connectiontype='${NodeConnectionType.AiOutputParser}'>output parser</a> on the canvas to specify the output format you require`,
 				name: 'notice',
@@ -454,17 +500,20 @@ export class ChainLlm implements INodeType {
 			0,
 		)) as BaseLanguageModel;
 
-		let outputParsers: BaseOutputParser[] = [];
-
-		if (this.getNodeParameter('hasOutputParser', 0, true) === true) {
-			outputParsers = (await this.getInputConnectionData(
-				NodeConnectionType.AiOutputParser,
-				0,
-			)) as BaseOutputParser[];
-		}
+		const outputParsers = await getOptionalOutputParsers(this);
 
 		for (let itemIndex = 0; itemIndex < items.length; itemIndex++) {
-			const prompt = this.getNodeParameter('prompt', itemIndex) as string;
+			let prompt: string;
+			if (this.getNode().typeVersion <= 1.2) {
+				prompt = this.getNodeParameter('prompt', itemIndex) as string;
+			} else {
+				prompt = getPromptInputByType({
+					ctx: this,
+					i: itemIndex,
+					inputKey: 'text',
+					promptTypeKey: 'promptType',
+				});
+			}
 			const messages = this.getNodeParameter(
 				'messages.messageValues',
 				itemIndex,