fix(core): guard message inspectors against empty parts arrays

packages/core/src/utils/messageInspectors.test.ts

@@ -0,0 +1,111 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import type { Content } from '@google/genai';
+import { isFunctionCall, isFunctionResponse } from './messageInspectors.js';
+
+describe('messageInspectors', () => {
+  describe('isFunctionResponse', () => {
+    it('returns true for a user message whose parts are all function responses', () => {
+      const content: Content = {
+        role: 'user',
+        parts: [
+          { functionResponse: { name: 'tool', response: { ok: true } } },
+          { functionResponse: { name: 'tool2', response: { ok: true } } },
+        ],
+      };
+      expect(isFunctionResponse(content)).toBe(true);
+    });
+
+    it('returns false when the role is not "user"', () => {
+      const content: Content = {
+        role: 'model',
+        parts: [{ functionResponse: { name: 'tool', response: { ok: true } } }],
+      };
+      expect(isFunctionResponse(content)).toBe(false);
+    });
+
+    it('returns false when a part is not a function response', () => {
+      const content: Content = {
+        role: 'user',
+        parts: [{ text: 'hello' }],
+      };
+      expect(isFunctionResponse(content)).toBe(false);
+    });
+
+    it('returns false when parts are mixed', () => {
+      const content: Content = {
+        role: 'user',
+        parts: [
+          { functionResponse: { name: 'tool', response: { ok: true } } },
+          { text: 'hello' },
+        ],
+      };
+      expect(isFunctionResponse(content)).toBe(false);
+    });
+
+    it('returns false when parts is undefined', () => {
+      const content: Content = { role: 'user' };
+      expect(isFunctionResponse(content)).toBe(false);
+    });
+
+    it('returns false when parts is an empty array', () => {
+      const content: Content = { role: 'user', parts: [] };
+      expect(isFunctionResponse(content)).toBe(false);
+    });
+  });
+
+  describe('isFunctionCall', () => {
+    it('returns true for a model message whose parts are all function calls', () => {
+      const content: Content = {
+        role: 'model',
+        parts: [
+          { functionCall: { name: 'tool', args: {} } },
+          { functionCall: { name: 'tool2', args: {} } },
+        ],
+      };
+      expect(isFunctionCall(content)).toBe(true);
+    });
+
+    it('returns false when the role is not "model"', () => {
+      const content: Content = {
+        role: 'user',
+        parts: [{ functionCall: { name: 'tool', args: {} } }],
+      };
+      expect(isFunctionCall(content)).toBe(false);
+    });
+
+    it('returns false when a part is not a function call', () => {
+      const content: Content = {
+        role: 'model',
+        parts: [{ text: 'hello' }],
+      };
+      expect(isFunctionCall(content)).toBe(false);
+    });
+
+    it('returns false when parts are mixed', () => {
+      const content: Content = {
+        role: 'model',
+        parts: [
+          { functionCall: { name: 'tool', args: {} } },
+          { text: 'hello' },
+        ],
+      };
+      expect(isFunctionCall(content)).toBe(false);
+    });
+
+    it('returns false when parts is undefined', () => {
+      const content: Content = { role: 'model' };
+      expect(isFunctionCall(content)).toBe(false);
+    });
+
+    it('returns false when parts is an empty array', () => {
+      const content: Content = { role: 'model', parts: [] };
+      expect(isFunctionCall(content)).toBe(false);
+    });
+  });
+});

packages/core/src/utils/messageInspectors.ts

@@ -10,6 +10,7 @@ export function isFunctionResponse(content: Content): boolean {
   return (
     content.role === 'user' &&
     !!content.parts &&
+    content.parts.length > 0 &&
     content.parts.every((part) => !!part.functionResponse)
   );
 }
@@ -18,6 +19,7 @@ export function isFunctionCall(content: Content): boolean {
   return (
     content.role === 'model' &&
     !!content.parts &&
+    content.parts.length > 0 &&
     content.parts.every((part) => !!part.functionCall)
   );
 }