Detect and warn about cyclic tool refs when schema depth errors are encountered (#5609)

Co-authored-by: Jacob Richman <[email protected]>

1 files changed, 125 insertions, 0 deletions

diff --git a/packages/core/src/tools/tools.test.ts b/packages/core/src/tools/tools.test.ts
new file mode 100644
index 00000000..9942d3a9
--- /dev/null
+++ b/packages/core/src/tools/tools.test.ts
@@ -0,0 +1,125 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { hasCycleInSchema } from './tools.js'; // Added getStringifiedResultForDisplay
+
+describe('hasCycleInSchema', () => {
+  it('should detect a simple direct cycle', () => {
+    const schema = {
+      properties: {
+        data: {
+          $ref: '#/properties/data',
+        },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(true);
+  });
+
+  it('should detect a cycle from object properties referencing parent properties', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        data: {
+          type: 'object',
+          properties: {
+            child: { $ref: '#/properties/data' },
+          },
+        },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(true);
+  });
+
+  it('should detect a cycle from array items referencing parent properties', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        data: {
+          type: 'array',
+          items: {
+            type: 'object',
+            properties: {
+              child: { $ref: '#/properties/data/items' },
+            },
+          },
+        },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(true);
+  });
+
+  it('should detect a cycle between sibling properties', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        a: {
+          type: 'object',
+          properties: {
+            child: { $ref: '#/properties/b' },
+          },
+        },
+        b: {
+          type: 'object',
+          properties: {
+            child: { $ref: '#/properties/a' },
+          },
+        },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(true);
+  });
+
+  it('should not detect a cycle in a valid schema', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        name: { type: 'string' },
+        address: { $ref: '#/definitions/address' },
+      },
+      definitions: {
+        address: {
+          type: 'object',
+          properties: {
+            street: { type: 'string' },
+            city: { type: 'string' },
+          },
+        },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(false);
+  });
+
+  it('should handle non-cyclic sibling refs', () => {
+    const schema = {
+      properties: {
+        a: { $ref: '#/definitions/stringDef' },
+        b: { $ref: '#/definitions/stringDef' },
+      },
+      definitions: {
+        stringDef: { type: 'string' },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(false);
+  });
+
+  it('should handle nested but not cyclic refs', () => {
+    const schema = {
+      properties: {
+        a: { $ref: '#/definitions/defA' },
+      },
+      definitions: {
+        defA: { properties: { b: { $ref: '#/definitions/defB' } } },
+        defB: { type: 'string' },
+      },
+    };
+    expect(hasCycleInSchema(schema)).toBe(false);
+  });
+
+  it('should return false for an empty schema', () => {
+    expect(hasCycleInSchema({})).toBe(false);
+  });
+});