fix(js/ai/generate): Allow for model to be optional (#3912)

Author: ssbushi

js/ai/src/generate.ts

@@ -45,6 +45,7 @@ import { Message } from './message.js';
 import {
   GenerateResponseChunkData,
   GenerateResponseData,
+  ResolvedModel,
   resolveModel,
   type GenerateActionOptions,
   type GenerateRequest,
@@ -494,7 +495,10 @@ export async function toGenerateActionOptions<
   registry: Registry,
   options: GenerateOptions<O, CustomOptions>
 ): Promise<GenerateActionOptions> {
-  const resolvedModel = await resolveModel(registry, options.model);
+  let resolvedModel: ResolvedModel<CustomOptions> | undefined;
+  if (options.model) {
+    resolvedModel = await resolveModel(registry, options.model);
+  }
   const tools = await toolsToActionRefs(registry, options.tools);
   const resources = await resourcesToActionRefs(registry, options.resources);
   const messages: MessageData[] = messagesFromOptions(options);
@@ -513,15 +517,15 @@ export async function toGenerateActionOptions<
   }
 
   const params: GenerateActionOptions = {
-    model: resolvedModel.modelAction.__action.name,
+    model: resolvedModel?.modelAction.__action.name,
     docs: options.docs,
     messages: messages,
     tools,
     resources,
     toolChoice: options.toolChoice,
     config: {
-      version: resolvedModel.version,
-      ...stripUndefinedOptions(resolvedModel.config),
+      version: resolvedModel?.version,
+      ...stripUndefinedOptions(resolvedModel?.config),
       ...stripUndefinedOptions(options.config),
     },
     output: options.output && {

js/ai/src/model-types.ts

@@ -381,7 +381,7 @@ export const GenerateActionOutputConfig = z.object({
 
 export const GenerateActionOptionsSchema = z.object({
   /** A model name (e.g. `vertexai/gemini-1.0-pro`). */
-  model: z.string(),
+  model: z.string().optional(),
   /** Retrieved documents to be used as context for this generation. */
   docs: z.array(DocumentDataSchema).optional(),
   /** Conversation history for multi-turn prompting when supported by the underlying model. */

js/ai/tests/generate/generate_test.ts

@@ -22,6 +22,7 @@ import { beforeEach, describe, it } from 'node:test';
 import {
   generate,
   generateStream,
+  toGenerateActionOptions,
   toGenerateRequest,
   type GenerateOptions,
 } from '../../src/generate.js';
@@ -339,6 +340,21 @@ describe('toGenerateRequest', () => {
   }
 });
 
+describe('toGenerateActionOptions', () => {
+  const registry = new Registry();
+
+  it('should return action options with undefined model', async () => {
+    const options: GenerateOptions = {
+      prompt: 'hello',
+    };
+    const actionOptions = await toGenerateActionOptions(registry, options);
+    assert.strictEqual(actionOptions.model, undefined);
+    assert.deepStrictEqual(actionOptions.messages, [
+      { role: 'user', content: [{ text: 'hello' }] },
+    ]);
+  });
+});
+
 describe('generate', () => {
   let registry: Registry;
   var echoModel: ModelAction;