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Fix: Wrap Gemini function response arrays in object to prevent API error #2745

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Merged
vijayupadya merged 2 commits into from
Jan 12, 2026
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Fix: Wrap Gemini function response arrays in object to prevent API error #2745

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Fix: Wrap Gemini function response arrays in object to prevent API error
bharatvansh Jan 8, 2026
5eccd05
Merge branch 'main' into fix/gemini-array-response
bharatvansh Jan 12, 2026
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2 changes: 1 addition & 1 deletion src/extension/byok/common/geminiMessageConverter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ function apiContentToGeminiContent(content: (LanguageModelTextPart | LanguageMod
// Handle case with text content (may also have images)
try {
responsePayload = JSON.parse(textContent);
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Copilot AI Jan 8, 2026

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Consider adding a comment explaining why arrays (and other primitive types) need to be wrapped in an object. This would help future maintainers understand the Gemini API requirement. For example:

// Wrap non-object values (arrays, primitives, null) in an object because
// Gemini's FunctionResponse expects response to be a google.protobuf.Struct (JSON Object)

This provides context about the API constraint that necessitates this wrapping behavior.

Suggested change
responsePayload = JSON.parse(textContent);
responsePayload = JSON.parse(textContent);
// Wrap non-object values (arrays, primitives, null) in an object because
// Gemini's FunctionResponse.response must be a google.protobuf.Struct (JSON object)

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if (typeof responsePayload !== 'object' || responsePayload === null) {
if (typeof responsePayload !== 'object' || responsePayload === null || Array.isArray(responsePayload)) {
responsePayload = { result: responsePayload };
}
} catch {
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18 changes: 18 additions & 0 deletions src/extension/byok/common/test/geminiMessageConverter.spec.ts
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Expand Up @@ -102,6 +102,24 @@ describe('GeminiMessageConverter', () => {
expect(fr.functionResponse.response).toEqual({ foo: 'bar' });
});

it('should wrap array responses in an object', () => {
const toolResult = new LanguageModelToolResultPart('listRepos_12345', [new LanguageModelTextPart('["repo1", "repo2"]')]);
const messages: LanguageModelChatMessage[] = [
{
role: LanguageModelChatMessageRole.Assistant,
content: [toolResult],
name: undefined
}
];

const result = apiMessageToGeminiMessage(messages);

expect(result.contents).toHaveLength(1);
expect(result.contents[0].role).toBe('user');
const fr: any = result.contents[0].parts![0];
expect(fr.functionResponse.response).toEqual({ result: ['repo1', 'repo2'] });
});
Comment on lines +105 to +121
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Copilot AI Jan 8, 2026

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While the test for array wrapping is good, the fix also wraps other primitive types (strings, numbers, booleans, null) in an object. Consider adding tests for these cases as well to ensure comprehensive coverage. For example:

  • Test with a string primitive: "simple string"
  • Test with a number: 42
  • Test with a boolean: true
  • Test with null: null

This would ensure that all code paths through the wrapping logic are tested.

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it('should be idempotent when called multiple times (no duplication)', () => {
const toolResult = new LanguageModelToolResultPart('doThing_12345', [new LMText('{"value":42}')]);
const messages: LanguageModelChatMessage[] = [
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