fix: allow f.object().array() as input field (#452)

The validation logic was missing a case for the 'object' type, which caused an error when f.object().array() was used as an input field. This commit adds the missing case to the validation logic and includes a test to verify the fix.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: google-labs-jules[bot]

src/ax/dsp/input-object-array.test.ts

@@ -0,0 +1,74 @@
+import { vi, describe, it, expect } from 'vitest';
+
+import { ax } from '../index.js';
+import { f } from './sig.js';
+
+const sig = f()
+  .input(
+    'items',
+    f
+      .object(
+        {
+          id: f.number('Index'),
+          name: f.string('Name'),
+        },
+        'Item'
+      )
+      .array()
+  )
+  .output(
+    'classifiedItems',
+    f
+      .object(
+        {
+          id: f.number('Index'),
+          label: f.string('Label'),
+        },
+        'Classification'
+      )
+      .array()
+  )
+  .build();
+
+const gen = ax(sig);
+
+import type { AxAIService, AxChatResponse } from '../ai/types.js';
+
+const llm: AxAIService = {
+  chat: vi.fn().mockResolvedValue({
+    results: [
+      {
+        index: 0,
+        content:
+          'Classified Items: [{"id": 0, "label": "A"}, {"id": 1, "label": "B"}]',
+      },
+    ],
+  } as AxChatResponse),
+  embed: vi.fn(),
+  getOptions: vi.fn().mockReturnValue({}),
+  setOptions: vi.fn(),
+  getName: vi.fn(),
+  getFeatures: vi.fn(),
+  getModelList: vi.fn(),
+  getMetrics: vi.fn(),
+  getLogger: vi.fn(),
+  getLastUsedChatModel: vi.fn(),
+  getLastUsedEmbedModel: vi.fn(),
+  getLastUsedModelConfig: vi.fn(),
+  getId: vi.fn(),
+};
+
+describe('f.object().array() on inputs', () => {
+  it('should not throw a validation error for valid input', async () => {
+    const result = await gen.forward(llm, {
+      items: [
+        { id: 0, name: 'Foo' },
+        { id: 1, name: 'Bar' },
+      ],
+    });
+    expect(result.classifiedItems).toEqual([
+      { id: 0, label: 'A' },
+      { id: 1, label: 'B' },
+    ]);
+  });
+});

src/ax/dsp/util.ts

@@ -33,6 +33,8 @@ export const validateValue = (
         return val instanceof Date || typeof val === 'string';
       case 'json':
         return typeof val === 'object' || typeof val === 'string';
+      case 'object':
+        return typeof val === 'object';
       default:
         return false; // Unknown or unsupported type
     }