[Bugfix][Tool Parser] Fix dropped streaming arguments in Jamba and InternLM2 parsers

[mosya415]

Purpose

When streaming tool calls, the first time a call's arguments become non-empty, the Jamba and InternLM2 parsers computed the streamed delta by locating the raw model delta text inside json.dumps(arguments) with str.index:

arguments_delta = cur_arguments_json[: cur_arguments_json.index(delta_text) + len(delta_text)]

The raw delta need not appear verbatim in the re-serialized JSON. It can carry structural text such as , "arguments": {...}, or the model may emit compact JSON whose spacing differs from what json.dumps produces. When the delta is not a substring of cur_arguments_json, str.index raises ValueError. The surrounding except swallows it into a None delta while leaving prev_tool_call_arr unadvanced, so when the arguments complete within that same delta nothing re-triggers the branch and the client silently receives a tool call with empty arguments. This happens realistically with coarse deltas, for example stream_interval > 1 or async scheduling.

Both parsers get the same fix. The delta is located with str.find instead of str.index. When the raw text is absent but the arguments are already complete (is_complete_json), they are sent whole rather than dropped. While they are still partial, the parser waits for more text instead of streaming the closing characters partial_json_parser appended, which would corrupt the accumulated arguments and break the incremental-streaming prefix invariant. This keeps the load-bearing truncation intact and matches the formatting-independent diff that the sibling cur_arguments and prev_arguments branch already uses.

The change is identical in both files (vllm/tool_parsers/jamba_tool_parser.py and vllm/tool_parsers/internlm2_tool_parser.py); they differ only in a variable name (new_text vs delta_text) and in what holds the parsable array.

This supersedes #48755, which fixed the same InternLM2 bug but dropped that load-bearing truncation and traded it for a subtler corruption; the author agreed to close it in favor of this PR.

Test Plan

pytest tests/tool_parsers/test_jamba_tool_parser.py \
       tests/tool_parsers/test_internlm2_tool_parser.py

Each parser gets a standalone streaming regression test that delivers the tool name in one delta and the whole arguments object in the next, which is exactly the coarse-delta shape that triggered the bug. InternLM2's shared-harness streaming cases are marked xfail ("streaming not fully implemented"), so a standalone test is used there rather than relying on the harness. Both are CPU-only.

Test Result

Both new tests fail on the pre-fix code (the ValueError: substring not found is swallowed, the arguments are dropped, and the streamed arguments stay empty) and pass after the fix. The existing tests in both files still pass.

Before fix:

FAILED test_jamba_tool_parser.py::test_extract_tool_calls_streaming_arguments_in_single_delta
FAILED test_internlm2_tool_parser.py::test_streaming_arguments_in_single_delta
2 failed

After fix:

2 passed

[claude]

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[mosya415]

cc @bbrowning @chuenchen309, this now covers both jamba and internlm2 with the same fix and supersedes #48755. Both have standalone streaming regression tests that fail pre-fix and pass after. Ready for a look, and the ready label to run CI when it looks good. Thanks!

[bbrowning]

@mosya415 Taking a look, but just a note that for the DCO check to pass it looks like you'll need to ensure the two commits have the same signed-off-by - they have the same name but separate emails at the moment.

[mosya415]

Thanks @bbrowning. DCO is green now. Ready whenever you have time.

[bbrowning]

Looks good - all the unit tests pass for these models and the logic is self-contained to just cleaning up the paths where .index would throw an error before.

[mosya415]

Thanks @bbrowning. The three red suites on the latest run are all unrelated to the parser change, and the previous CI run on this branch, one merge commit earlier with the identical diff, passed all of them green.

speech-to-text is the known WER flake: evaluate.load("wer") hits hf_api.HfFolder.get_token() on a metric-cache miss, which no longer exists in huggingface-hub v1. It is fixed separately in #49801.

entrypoints-integration-api-server-openai-part is a Hypothesis property test that found a nondeterministic failing example while fuzzing the chat completions schema (it printed a @reproduce_failure(...) marker), unrelated to tool parsing.

entrypoints-integration-pooling is a rerank numerical tolerance drift in test_rerank_api_instruction_field_matches_chat_template_kwargs (about 0.0023 absolute), also unrelated.

Could you retry these jobs or merge when you have a moment? Nothing in the changed parsers touches these paths. Thanks!

[bbrowning]

They all passed with a retry - thanks for helping me work through the CI here!