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Add truncated response handling for Google empty content #171

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Merged
Ken Jiang (knjiang) merged 2 commits into from
Apr 1, 2026
Merged

Add truncated response handling for Google empty content #171

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006fc08
fix errors from when max_tokens is lower than 1 character response
knjiang Apr 1, 2026
de3a48f
fix small bug
knjiang Apr 1, 2026
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9 changes: 9 additions & 0 deletions crates/coverage-report/src/requests_expected_differences.json
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Original file line number Diff line number Diff line change
Expand Up @@ -440,6 +440,15 @@
"fields": [
{ "pattern": "messages.length", "reason": "Parallel tool results grouped in one Tool message expand to separate function_call_output items in Responses API" }
]
},
{
"testCase": "simpleRequestTruncated",
"source": "Google",
"target": "*",
"fields": [
{ "pattern": "messages[*].content", "reason": "Empty assistant content (no parts) from truncated Gemini response gains a placeholder empty text part when roundtripped through other providers" },
{ "pattern": "messages.length", "reason": "Empty assistant content from truncated Gemini response may change message count when roundtripped through providers that split/merge messages" }
]
}
]
}
9 changes: 9 additions & 0 deletions crates/coverage-report/src/responses_expected_differences.json
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Original file line number Diff line number Diff line change
Expand Up @@ -283,6 +283,15 @@
"fields": [
{ "pattern": "messages.length", "reason": "Google reasoning content expands to separate output items in Responses format" }
]
},
{
"testCase": "simpleRequestTruncated",
"source": "Google",
"target": "*",
"fields": [
{ "pattern": "messages[*].content", "reason": "Empty assistant content (no parts) from truncated Gemini response gains a placeholder empty text part when roundtripped through other providers" },
{ "pattern": "messages.length", "reason": "Empty assistant content from truncated Gemini response may change message count when roundtripped through providers that split/merge messages" }
]
}
]
}
16 changes: 12 additions & 4 deletions crates/lingua/src/providers/google/convert.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,9 +121,17 @@ impl TryFromLLM<GoogleContent> for Message {
.ok_or(ConvertError::MissingRequiredField {
field: "role".to_string(),
})?;
let parts = content.parts.ok_or(ConvertError::MissingRequiredField {
field: "parts".to_string(),
})?;
// Only allow missing parts for "model" role — Gemini may omit parts when
// maxOutputTokens is exhausted (MAX_TOKENS finish reason). For other roles,
// missing parts means this isn't a Google-format message (e.g. Anthropic
// messages have "content" not "parts").
let parts: Vec<GooglePart> = if role == "model" {
content.parts.unwrap_or_default()
} else {
content.parts.ok_or(ConvertError::MissingRequiredField {
field: "parts".to_string(),
})?
};

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@knjiang Ken Jiang (knjiang) Apr 1, 2026

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this was causing the error:

FAILED test_openai.py::test_max_tokens - Failed: gemini-2.5-flash: BadRequestError: Conversion to universal format failed: Missing required field: parts

the new response is now:

{
  "choices": [
    {
      "finish_reason": "length",
      "index": 0,
      "message": {
        "annotations": [],
        "role": "assistant",
      },
    },
  ],
  "created": 0,
  "id": "chatcmpl-transformed",
  "model": "gemini-2.5-flash",
  "object": "chat.completion",
  "usage": {
    "completion_tokens": 0,
    "prompt_tokens": 10,
    "total_tokens": 10,
  },
}
`;

match role {
"model" => {
Expand Down Expand Up @@ -454,7 +462,7 @@ impl TryFromLLM<Message> for GoogleContent {

Ok(GoogleContent {
role: Some(role),
parts: Some(parts),
parts: if parts.is_empty() { None } else { Some(parts) },
})
}
}
Expand Down
47 changes: 47 additions & 0 deletions payloads/cases/simple.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,53 @@ export const simpleCases: TestCaseCollection = {
},
},

simpleRequestTruncated: {
"chat-completions": {
model: OPENAI_CHAT_COMPLETIONS_MODEL,
messages: [
{
role: "user",
content: "Write a very long essay about the ocean.",
},
],
max_completion_tokens: 1,
},
responses: {
model: OPENAI_RESPONSES_MODEL,
max_output_tokens: 1,
input: [
{
role: "user",
content: "Write a very long essay about the ocean.",
},
],
},
anthropic: {
model: ANTHROPIC_MODEL,
max_tokens: 1,
messages: [
{
role: "user",
content: "Write a very long essay about the ocean.",
},
],
},
google: {
contents: [
{
role: "user",
parts: [{ text: "Write a very long essay about the ocean." }],
},
],
generationConfig: {
maxOutputTokens: 1,
},
},
bedrock: null,
"bedrock-anthropic": null,
"vertex-anthropic": null,
},

toolCallRequest: {
"chat-completions": {
model: OPENAI_CHAT_COMPLETIONS_MODEL,
Expand Down
92 changes: 92 additions & 0 deletions payloads/scripts/transforms/__snapshots__/transforms-streaming.test.ts.snap
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