[Rust Frontend] Tolerate whitespace before the outer brace in JSON tool-call parsers (#48034)

Signed-off-by: Tahsin Tunan <tahsintunan@gmail.com>

rust/src/chat/src/output/default/unified.rs

@@ -451,6 +451,57 @@ mod tests {
         output
     }
 
+    #[tokio::test]
+    async fn unified_stream_parses_formatted_tool_call_without_latch() {
+        use vllm_parser::tool::{HermesToolParser, ToolParser as _};
+
+        let hermes = HermesToolParser::create(&[]).unwrap();
+        let parser = vllm_parser::unified::CombinedParser::new(None, Some(hermes));
+
+        // Regression guard: a formatted call (space before the outer `}`) must not
+        // trip the parse-error latch that turns it and every later call into text.
+        let d1 = decoded_delta(
+            r#"<tool_call>{"name":"get_weather","arguments":{"location":"Paris"} }</tool_call>"#,
+        );
+        let d2 = finished_delta(
+            r#"<tool_call>{"name":"get_time","arguments":{"tz":"UTC"}}</tool_call>"#,
+        );
+
+        let stream = stream::iter(vec![d1, d2].into_iter().map(Ok));
+        let events = unified_event_stream(stream, Box::new(parser))
+            .collect::<Vec<_>>()
+            .await
+            .into_iter()
+            .collect::<crate::Result<Vec<_>>>()
+            .unwrap();
+
+        let names: Vec<&str> = events
+            .iter()
+            .filter_map(|event| match event {
+                AssistantEvent::ToolCallStart { name, .. } => Some(name.as_str()),
+                _ => None,
+            })
+            .collect();
+        assert_eq!(names, ["get_weather", "get_time"]);
+
+        let text_leaks = events
+            .iter()
+            .filter(|event| {
+                matches!(
+                    event,
+                    AssistantEvent::TextDelta {
+                        kind: AssistantBlockKind::Text,
+                        ..
+                    }
+                )
+            })
+            .count();
+        assert_eq!(
+            text_leaks, 0,
+            "formatted tool call leaked into text: {events:#?}"
+        );
+    }
+
     #[tokio::test]
     async fn unified_stream_emits_reasoning_only_deltas() {
         let events = collect(

rust/src/parser/src/tool/json/llama.rs

@@ -238,7 +238,9 @@ fn parse_llama_arguments_event(
 
 /// Parse the outer closing brace for one Llama JSON tool call.
 fn tool_call_close_event(input: &mut JsonToolInput<'_>) -> ModalResult<LlamaJsonEvent> {
-    literal("}").value(LlamaJsonEvent::ToolCallClose).parse_next(input)
+    seq!(_: ws0, _: literal("}"))
+        .value(LlamaJsonEvent::ToolCallClose)
+        .parse_next(input)
 }
 
 /// Parse a semicolon separator after one Llama JSON tool call.
@@ -266,6 +268,28 @@ mod tests {
         format!(r#"{{"name":"{function_name}","parameters":{parameters}}}"#)
     }
 
+    #[test]
+    fn llama_tolerates_whitespace_before_outer_brace() {
+        // Whitespace between the parameters object's `}` and the outer `}` must
+        // still parse (json.loads / raw_decode parity).
+        let mut whole = Llama3JsonToolParser::new(&test_tools());
+        let whole_output = whole.parse_complete(r#"{"name":"f","parameters":{"x":1} }"#).unwrap();
+        assert_eq!(whole_output.calls().len(), 1);
+        assert_eq!(whole_output.calls()[0].name.as_deref(), Some("f"));
+        assert_eq!(whole_output.calls()[0].arguments, r#"{"x":1}"#);
+
+        // Same input, whitespace before the outer `}` split across a chunk boundary.
+        let mut chunked = Llama3JsonToolParser::new(&test_tools());
+        let mut output = ToolParserOutput::default();
+        for chunk in [r#"{"name":"f","parameters":{"x":1}"#, " ", "}"] {
+            output.append(chunked.parse_chunk(chunk).unwrap());
+        }
+        output.append(chunked.finish().unwrap());
+        let output = output.coalesce();
+        assert_eq!(output.calls().len(), 1);
+        assert_eq!(output.calls()[0].arguments, r#"{"x":1}"#);
+    }
+
     #[test]
     fn llama_json_parse_complete_without_tool_call_keeps_text() {
         let mut parser = Llama3JsonToolParser::new(&test_tools());

rust/src/parser/src/tool/json/mod.rs

@@ -317,7 +317,7 @@ fn tool_call_close_event(
     input: &mut JsonToolInput<'_>,
     config: JsonToolCallConfig,
 ) -> ModalResult<JsonToolCallEvent> {
-    let _ = literal("}").parse_next(input)?;
+    seq!(_: ws0, _: literal("}")).parse_next(input)?;
 
     match config.delimiter {
         Some(delimiter) => alt((
@@ -406,6 +406,34 @@ mod tests {
         output.coalesce()
     }
 
+    #[test]
+    fn json_tool_call_tolerates_whitespace_before_outer_brace() {
+        // Pretty-printed JSON puts whitespace between the arguments object's `}`
+        // and the outer object's `}`; it must still parse (json.loads parity).
+        let mut whole = JsonToolCallParser::new(DELIMITED_CONFIG);
+        let whole_output = collect_chunks(
+            &mut whole,
+            &[r#"<tool_calls>{"function":"f","parameters":{"x":1} }</tool_calls>"#],
+        );
+        assert_eq!(whole_output.calls().len(), 1);
+        assert_eq!(whole_output.calls()[0].name.as_deref(), Some("f"));
+        assert_eq!(whole_output.calls()[0].arguments, r#"{"x":1}"#);
+
+        // Same input, but the whitespace before the outer `}` is split across a
+        // chunk boundary (exercises `ws0` returning Incomplete on `Partial`).
+        let mut chunked = JsonToolCallParser::new(DELIMITED_CONFIG);
+        let chunked_output = collect_chunks(
+            &mut chunked,
+            &[
+                r#"<tool_calls>{"function":"f","parameters":{"x":1}"#,
+                " ",
+                "}</tool_calls>",
+            ],
+        );
+        assert_eq!(chunked_output.calls().len(), 1);
+        assert_eq!(chunked_output.calls()[0].arguments, r#"{"x":1}"#);
+    }
+
     #[test]
     fn json_tool_call_delimiter_extracts_multiple_calls_in_one_block() {
         let input = build_tool_calls(&[