feat: add finish reason = tool_calls for stream=False and phi-4 detect token start fix (#3087)

Signed-off-by: Elyas Mehtabuddin <[email protected]>

Author: elyasmnvidian

lib/bindings/python/Cargo.lock

@@ -181,10 +181,13 @@ impl DeltaAggregator {
                                 .collect();
 
                             // Initialize and push the converted tool calls to state_choice.tool_calls
-                            if let Some(existing_tool_calls) = &mut state_choice.tool_calls {
-                                existing_tool_calls.extend(converted_tool_calls);
-                            } else {
-                                state_choice.tool_calls = Some(converted_tool_calls);
+                            // Only set tool_calls to Some if there are actual tool calls
+                            if !converted_tool_calls.is_empty() {
+                                if let Some(existing_tool_calls) = &mut state_choice.tool_calls {
+                                    existing_tool_calls.extend(converted_tool_calls);
+                                } else {
+                                    state_choice.tool_calls = Some(converted_tool_calls);
+                                }
                             }
                         }
 
@@ -257,6 +260,17 @@ impl From<DeltaChoice> for dynamo_async_openai::types::ChatChoice {
     /// # Note
     /// The `function_call` field is deprecated.
     fn from(delta: DeltaChoice) -> Self {
+        // If tool calls are present and non-empty, finish reason should be ToolCalls
+        let finish_reason = if delta
+            .tool_calls
+            .as_ref()
+            .is_some_and(|calls| !calls.is_empty())
+        {
+            Some(dynamo_async_openai::types::FinishReason::ToolCalls)
+        } else {
+            delta.finish_reason
+        };
+
         dynamo_async_openai::types::ChatChoice {
             message: dynamo_async_openai::types::ChatCompletionResponseMessage {
                 role: delta.role.expect("delta should have a Role"),
@@ -272,7 +286,7 @@ impl From<DeltaChoice> for dynamo_async_openai::types::ChatChoice {
                 reasoning_content: delta.reasoning_content,
             },
             index: delta.index,
-            finish_reason: delta.finish_reason,
+            finish_reason,
             logprobs: delta.logprobs,
         }
     }
@@ -347,7 +361,7 @@ mod tests {
             tool_calls.map(|tool_calls| serde_json::from_str(tool_calls).unwrap());
 
         let tool_call_chunks = if let Some(tool_calls) = tool_calls {
-            vec![
+            Some(vec![
                 dynamo_async_openai::types::ChatCompletionMessageToolCallChunk {
                     index: 0,
                     id: Some("test_id".to_string()),
@@ -357,22 +371,15 @@ mod tests {
                         arguments: Some(serde_json::to_string(&tool_calls["arguments"]).unwrap()),
                     }),
                 },
-            ]
+            ])
         } else {
-            vec![
-                dynamo_async_openai::types::ChatCompletionMessageToolCallChunk {
-                    index: 0,
-                    id: None,
-                    r#type: None,
-                    function: None,
-                },
-            ]
+            None
         };
 
         let delta = dynamo_async_openai::types::ChatCompletionStreamResponseDelta {
             content: Some(text.to_string()),
             function_call: None,
-            tool_calls: Some(tool_call_chunks),
+            tool_calls: tool_call_chunks,
             role,
             refusal: None,
             reasoning_content: None,
@@ -625,6 +632,215 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn test_tool_calling_finish_reason_override_from_stop() {
+        // Test that when tool calls are present but finish reason is Stop, it gets overridden to ToolCalls
+        let tool_call_json =
+            r#"{"name": "get_weather", "arguments": {"location": "New York", "unit": "celsius"}}"#;
+
+        let annotated_delta = create_test_delta(
+            0,
+            "I'll check the weather for you.",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            Some(dynamo_async_openai::types::FinishReason::Stop), // Original finish reason is Stop
+            None,
+            Some(tool_call_json),
+        );
+
+        let data = annotated_delta.data.unwrap();
+        let annotated_delta = Annotated {
+            data: Some(data),
+            id: Some("test_id".to_string()),
+            event: None,
+            comment: None,
+        };
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        assert!(result.is_ok());
+        let response = result.unwrap();
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // Verify tool calls are present
+        assert!(choice.message.tool_calls.is_some());
+        let tool_calls = choice.message.tool_calls.as_ref().unwrap();
+        assert_eq!(tool_calls.len(), 1);
+
+        // Most importantly, verify that finish reason was overridden to ToolCalls despite original being Stop
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::ToolCalls)
+        );
+    }
+
+    #[tokio::test]
+    async fn test_tool_calling_finish_reason_override_from_length() {
+        // Test that when tool calls are present but finish reason is Length, it gets overridden to ToolCalls
+        let tool_call_json = r#"{"name": "search", "arguments": {"query": "rust programming"}}"#;
+
+        let annotated_delta = create_test_delta(
+            0,
+            "Let me search for that.",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            Some(dynamo_async_openai::types::FinishReason::Length), // Original finish reason is Length
+            None,
+            Some(tool_call_json),
+        );
+
+        let data = annotated_delta.data.unwrap();
+        let annotated_delta = Annotated {
+            data: Some(data),
+            id: Some("test_id".to_string()),
+            event: None,
+            comment: None,
+        };
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        assert!(result.is_ok());
+        let response = result.unwrap();
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // Verify tool calls are present
+        assert!(choice.message.tool_calls.is_some());
+        let tool_calls = choice.message.tool_calls.as_ref().unwrap();
+        assert_eq!(tool_calls.len(), 1);
+
+        // Verify that finish reason was overridden to ToolCalls despite original being Length
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::ToolCalls)
+        );
+    }
+
+    #[tokio::test]
+    async fn test_tool_calling_finish_reason_override_from_none() {
+        // Test that when tool calls are present but finish reason is None, it gets set to ToolCalls
+        let tool_call_json = r#"{"name": "calculate", "arguments": {"expression": "2+2"}}"#;
+
+        let annotated_delta = create_test_delta(
+            0,
+            "I'll calculate that for you.",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            None, // Original finish reason is None
+            None,
+            Some(tool_call_json),
+        );
+
+        let data = annotated_delta.data.unwrap();
+        let annotated_delta = Annotated {
+            data: Some(data),
+            id: Some("test_id".to_string()),
+            event: None,
+            comment: None,
+        };
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        assert!(result.is_ok());
+        let response = result.unwrap();
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // Verify tool calls are present
+        assert!(choice.message.tool_calls.is_some());
+        let tool_calls = choice.message.tool_calls.as_ref().unwrap();
+        assert_eq!(tool_calls.len(), 1);
+
+        // Verify that finish reason was set to ToolCalls despite original being None
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::ToolCalls)
+        );
+    }
+
+    #[tokio::test]
+    async fn test_no_tool_calling_preserves_original_finish_reason() {
+        // Test that when no tool calls are present, the original finish reason is preserved
+        let annotated_delta = create_test_delta(
+            0,
+            "This is a regular response without tool calls.",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            Some(dynamo_async_openai::types::FinishReason::Stop),
+            None,
+            None, // No tool calls
+        );
+
+        let data = annotated_delta.data.unwrap();
+        let annotated_delta = Annotated {
+            data: Some(data),
+            id: Some("test_id".to_string()),
+            event: None,
+            comment: None,
+        };
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        assert!(result.is_ok());
+        let response = result.unwrap();
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // Verify no tool calls are present
+        assert!(choice.message.tool_calls.is_none());
+
+        // Verify that original finish reason (Stop) is preserved
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::Stop)
+        );
+    }
+
+    #[tokio::test]
+    async fn test_empty_tool_calls_preserves_original_finish_reason() {
+        // Test that when tool calls array is empty, the original finish reason is preserved
+        // Create a delta with empty tool calls by modifying the create_test_delta output
+        let mut annotated_delta = create_test_delta(
+            0,
+            "Response with empty tool calls array.",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            Some(dynamo_async_openai::types::FinishReason::Length),
+            None,
+            None,
+        );
+
+        // Manually set empty tool calls array
+        if let Some(ref mut data) = annotated_delta.data {
+            data.choices[0].delta.tool_calls = Some(vec![]); // Empty tool calls array
+        }
+
+        let data = annotated_delta.data.unwrap();
+        let annotated_delta = Annotated {
+            data: Some(data),
+            id: Some("test_id".to_string()),
+            event: None,
+            comment: None,
+        };
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        assert!(result.is_ok());
+        let response = result.unwrap();
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // Verify tool calls array is empty
+        assert!(choice.message.tool_calls.is_none());
+
+        // Verify that original finish reason (Length) is preserved since tool calls are empty
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::Length)
+        );
+    }
+
     #[tokio::test]
     async fn test_tool_calling_output() {
         // Simulate a delta with a tool call in the content
@@ -688,4 +904,45 @@ mod tests {
             dynamo_async_openai::types::Role::Assistant
         );
     }
+
+    #[tokio::test]
+    async fn test_tool_calling_finish_reason_override_from_stop_alternative() {
+        // Test that when tool calls are present but finish reason is Stop, it gets overridden to ToolCalls
+        let tool_call_json =
+            r#"{"name": "get_weather", "arguments": {"location": "New York", "unit": "celsius"}}"#;
+
+        let annotated_delta = create_test_delta(
+            0,
+            "Getting weather for New York",
+            Some(dynamo_async_openai::types::Role::Assistant),
+            Some(dynamo_async_openai::types::FinishReason::Stop), // This should be overridden
+            None,
+            Some(tool_call_json),
+        );
+
+        let stream = Box::pin(stream::iter(vec![annotated_delta]));
+
+        // Call DeltaAggregator::apply
+        let result = DeltaAggregator::apply(stream, ParsingOptions::default()).await;
+
+        // Check the result
+        assert!(result.is_ok());
+        let response = result.unwrap();
+
+        // There should be one choice
+        assert_eq!(response.choices.len(), 1);
+        let choice = &response.choices[0];
+
+        // The finish_reason should be ToolCalls, not Stop, because tool calls are present
+        assert_eq!(
+            choice.finish_reason,
+            Some(dynamo_async_openai::types::FinishReason::ToolCalls)
+        );
+
+        // Verify tool calls are present
+        assert!(choice.message.tool_calls.is_some());
+        let tool_calls = choice.message.tool_calls.as_ref().unwrap();
+        assert_eq!(tool_calls.len(), 1);
+        assert_eq!(tool_calls[0].function.name, "get_weather");
+    }
 }